Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session CP11: Poster Session II: Basic Plasma Physics; Boundary, PMI, ProtoMPEX; International Tokamaks; Turbulence and Transport; Other Configurations; Zpinch, Dense Plasma Focus and MagLIF (2:00pm5:00pm) 
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Room: OCC Exhibit Hall A1&A 

CP11.00001: Effects of Multipactor on the Quality of a Signal Patrick Wong, Yue Ying Lau, Peng Zhang Multipactor is a much studied AC discharge [1,2] that is harmful to microwave components. There is substantial current interest on this topic because of its threat to satellite communications [3]. In this paper, we present an analytical model to assess the effects of multipactor on the distortion of a signal. Extensions to multitone and modulated signals will also be attempted. [1] J. R. M. Vaughan, IEEE TED, Vol. 35, No. 7, 1988. [2] R. A. Kishek et al., Physics of Plasmas 5, 2120 (1998). [3] Special sessions on Multipactor, I and II, ICOPS, Denver, CO, June 2018.  

CP11.00002: Ablation of HighZ Pellets in Hot Plasma Adrian Kristopher Fontanilla, Boris Breizman How pellet material is ablated and assimilated into plasma is relevant to disruption mitigation via impurity injection. The pellet ablation rate is determined by the power deposited by the incident fast electrons. The present work describes fast electrons within the pellet material selfconsistently from the kinetic equation that includes electron scattering. Prior efforts to calculate the power deposition kinetically have been reported in Ref. [1] (for C pellets) and Ref.[2][3] (for H). Our work focuses on highZ pellet material in which case Z is an ordering parameter. To lowest order in Z, the distribution function of the incident electrons is nearly isotropic, and the electrons diffuse spatially in the ablation cloud until they lose energy due to collisional friction. We consider two limits: one in which the cloud geometry is 1d and another in which the geometry is 3d but the cloud is nearly transparent. A perturbative procedure is then presented that relaxes the transparent constraint. [1] B.V. Kuteev, et al, Sov. J. Plasma Phys. 10, 6 (1984) [2] A.K. MacAulay, NF 34, 43 (1994) [3] R. Ishizaki, et al, PoP 11, 8 (2004)  

CP11.00003: Numerical analysis of Debye shielding by Nbody simulation Yasuutaro Nishimura, ChengPu Wang Basic properties of Debye shielding is investigated by directly calculating Coulomb force between the charged particles. Learning from Nbody gravity simulation, numerical techniques are employed to avoid singularities when potential energy between two charged particles become comparable to the kinetic energy. Electron distribution function in Debye shielding is analyzed, which deviates from conventional Maxwellian distribution function.  

CP11.00004: Electron collision term due to reflections in electronelectron collisions in a magnetized plasma Chao Dong, Ding Li For a electronelectron (ee) collision with impact parameter p between the electron thermal gyroradius ρ_{th }and the Debye length λ_{D}, ρ_{th}<p<λ_{D}, when the initial relative parallel kinetic energy is smaller than the Coulomb repulsive potential e^{2}/(4πε_{0}p), reflection will occur with interchange of the parallel velocities of the two electrons after the collision. The FokkerPlanck approach is employed to derive the electron collision term C_{R} due to the reflection. The electron parallel velocity friction and diffusion coefficients <Δv_{z}>_{R}, <Δv_{z}Δv_{z}>_{R} are calculated which depend insensitively on the electron perpendicular velocity v_{perp}. For Maxwellian background electrons, when v_{z}<<v_{th}, <Δv_{z}>_{R} and <Δv_{z}Δv_{z}>_{R} are found to be, respectively, three times the corresponding results of the no magnetic field case with v<<v_{th}, where v, v_{z}, and v_{th }are the electron speed, parallel velocity, and the background electron thermal velocity, respectively. When v_{z}>>v_{th}, <Δv_{z}>_{R} and <Δv_{z}Δv_{z}>_{R} are exponentially small as the number of ee collisions with reflections is exponentially small in this case. Through studying the time evolution of the quantity H under the effect of C_{R}, it is surprising to find that C_{R} finally makes the electron distribution f_{e}(v) relax to the form f_{e}(v)=F_{e}(v_{perp})G_{e}(v_{z}).  

CP11.00005: Magnetic Fields in Indirect Drive Inertial Confinement Fusion Christopher Alexander Walsh Plasma magnetisation effects are routinely ignored in the design and interpretation of laserdriven inertial confinement fusion (ICF) experiments. The presented work uses the 3D extendedmagnetohydrodynamics code Chimera to simulate both the impact of selfgenerated magnetic fields on the hotspot cooling process and assess the anticipated increase in fusion performance through the application of external magnetic fields. Magnetic fields are spontaneously generated during ICF implosions by the Biermann battery process when the capsule is not spherically symmetric. During stagnation, the hotspot edge contains large magnetic field intensities, estimated to be up to 10,000T in strength. Subsequent magnetisation of the electron population can reduce thermal conductivities by 90%. Externallyapplied magnetic fields can be used to enhance the fusion yield by magnetising both the electron and αparticle populations in the hotspot, increasing the energy containment. Modifications to hotspot shape are explored by using perturbations relevant to the highfoot (radiation asymmetry and tent scar) and HDC (filltube) campaigns. Highmode perturbations are also simulated, suggesting reductions of mix into the hotspot due to magnetic tension suppressing vortices.  

CP11.00006: Breaking the CIV speed limit in a rotating plasma device Ashley Stiles, Karin w Fulford, James P Patton, Remington R Reid, David l Cooke
The critical ionization velocity (CIV) was first proposed by Hannes Alfven [1954] as a mechanism for ionization in a neutral gas streaming through a magnetized plasma. The newly born pickup ions act as momentum loading and restrain the relative velocity. The velocity and rate of ionization depend on how the momentum can be coupled by currents to distant plasma or to nearby conductors. Maintaining ionization requires power, and increasing the velocity beyond the CIV rapidly increases the power requirement. Thus CIV acts as an effective speed limit. To study this and other aspects of momentum coupling, we have built a cylindrical plasma device with an axial magnetic field. A plasma with a radial electric field is established using hollow cathode electron and ion emitters as virtual electrodes, with glass end caps to support the radial electric field. This device produces an ExB rotating plasma and we observe a rapidly increasing power requirement approaching the CIV velocity. There are however, applications where it is desired to exceed the CIV limit. Thus this experiment will explore the practical dependence of CIV on parameters such as power, magnetic field, momentum coupling, and in particular the neutral gas density.  

CP11.00007: Overview of Experiments at the Wisconsin Plasma Physics Laboratory Cary Forest, the WiPPL Team During the past year, the Wisconsin Plasma Physics Laboratory has been formed to operate several devices asa a DoE User Facility for Frontier Plasma Physics. The devices include the Madison Symmtric Torus, constructed and supported by the DoE for many years for fusion research and the Big Red Ball device constructed with support from the NSF. This poster will present an overview of the transition to a User Facility and an introduction to how users can become engaged. It will also provide highlights of scientific progress, including recent results on reconnection, dynamos, turbulence, and particle acceleration from both devices.  

CP11.00008: Strong magnetic field amplification in quasiKeplerian highβ plasma flows Ken Flanagan, Jason M Milhone, Mark D Nornberg, Cary B Forest QuasiKeplerian flows in the Big Red Ball (BRB) develop a peaked axial magnetic field approximately an order of magnitude larger than the applied field. The method of stirring, volumetric flow drive (VFD), consists of forcing current injected by biased cathodes to cross a weak (ν_{ii} » Ω_{ci}) externally applied field using a Helmholtz coil set. Flows can reach a Mach number of M∼0.3 with β∼100 and δ_{i}/L∼1. The magnetic field amplification is observed in spherical NIMROD simulations only when including the Hall term in Ohm’s law and when the injected current is directed radially outwards at the equator. The magnetic flux increase results from conversion of toroidal flux from the injected current into poloidal flux by the Hall effect. In the experiment there are also significant pressure gradients due to losses along open field lines in the core that cause poloidal flux to peak in the core via the diamagnetic effect. These observations suggest mechanisms important to magnetic induction beyond MHD in unmagnetized plasmas.  

CP11.00009: Theta Pinch Collisionless Shock Experiment on the Big Red Ball Douglass Endrizzi, Cary B Forest, Adam J Stanier, Jan Egedal, Joseph R Olson A highbeta theta pinch collisionless shock experiment was performed on the big red ball. Cylindrical VPIC simulations were used to interpret experimental results. HallMHD in this cylindrical geometry mostly succeeds in explaining results via the following mechanism: the fast thetapinch field affects the magnetized electron fluid, creating an ExB drift inward. The resultant charge separation serves to pull ions inward, with ion inertia slowing the current layer. Reflected ions that move at twice the piston speed are observed, as are resonant ions that ‘surf’ the compressing wave inward. The experiment and simulation were repeated in the strongly magnetized regime and compared with pure MHD. Whether the reflected ions could lead to a collisionless shock through Buneman, Weibel, or other instabilities is explored.  

CP11.00010: Measuring Plasma Viscosity with a FabryPerot Spectrometer Jason Milhone, Ken Flanagan, Mark D Nornberg, Cary B. Forest A FabryPerot spectrometer has been developed for measuring ion temperature and inferring the Braginskii viscosity of flowing, unmagnetized plasmas at WiPPL. Ion viscosity is important in coupling the momentum from JxB edgedriven flows throughout the plasma to generate largescale shear flow. In a FabryPerot spectrometer, collimated light is dispersed by an etalon to provide highthroughput, compact, and simple optical design with high resolvingpower. The precision needed to measure the fixed etalon plate separation for an absolute wavelength calibration at high order motivates an analysis using multimodal nested sampling. An experiment has been designed to measure the ion viscosity and the momentum diffusion length of JxB edgedriven flows on the PCXU using the FabryPerot spectrometer and to compare against Machprobe velocity profiles and Braginskii viscosity.  

CP11.00011: Experimental platforms for plasma turbulence studies at WiPPL K. J. McCollam, D. A. Endrizzi, C. B. Forest, J. M. Milhone, M. D. Nornberg, E. E. Peterson, J. S. Sarff, E. M. SuenLewis Both the spherical BRB device and the toroidal MST device provide opportunities for plasma turbulence experiments at the Wisconsin Plasma Physics Laboratory (WiPPL) to both internal and external users of the facility. Plasma gun arrays and compacttoroid (CT) injectors are being developed as sources to enable a variety of turbulence scenarios. In BRB, electrostatically biased plasma gun arrays produce rotating helical flux ropes along an axial magnetic field, driving magnetic relaxation and energizing what appear to be Alfvenic and ion cyclotron fluctuations observed up to frequencies of order 100 kHz. Colliding CTs with stationary grids may allow control of the injection scale for studies of magnetized plasma turbulent cascades. Colliding CTs with each other may produce shocks and turbulent structures which could generate magnetic energy or accelerate particles up to suprathermal energies. In MST, the energy input by colliding CTs or flux ropes might interact with the strong turbulent cascade produced by reversedfield pinch current relaxation.  

CP11.00012: Densitymagnetic field correlation studies for characterizing the turbulence content in the SSX plasma Manjit Kaur, M. R. Brown, David A Schaffner Turbulence is of great interest in magnetized plasmas and can be determined by carrying out a frequency power spectrum in the fluctuations present in the turbulent quantities. However, the power spectrum does not shed light on the underlying physical mechanisms at play. To address this issue, one may consider the turbulent fluctuations as primarily originating from the nonlinear interaction of linear MHD modes. This type of analysis has been used in solar wind turbulence observations to determine the proportion of fast and slow wave content in the turbulent plasma^{1}. The different wave modes can be distinguished by determining the correlation between the fluctuations in the density and the colocated magnetic field aligned component. In this poster, we will present the preliminary results obtained by carrying out the correlation analysis on the fluctuations present in the density and the colocated magnetic field. These studies are carried out on the SSX device, where we generate a spheromak which then tilts and relaxes to a twisted structure. The relaxation process is highly turbulent in nature and in this phase, the plasma is used for carrying out these studies. ^{1}Howes et. al., Ap. J. Lett. 753, L19 (2013).
 

CP11.00013: Turbulent Fluctuations in a FluxRope Plasma at the Big Red Ball Emma M. SuenLewis, Cary B. Forest, Michael R Brown, Douglass Endrizzi, Karsten J McCollam, David A Schaffner, Jason M Milhone, Ethan E Peterson, Mark D Nornberg Observations of flux rope plasmas in the spherical BRB device at WiPPL are used to study turbulence and magnetic relaxation in plasma with beta between 0.251, flow speeds of approximately 20 km/s, and dB/B of approximately 12%. The flux ropes are generated via three plasma guns electrically biased relative to an anode on the opposite pole of the sphere, creating a current across the device. Magnetic fields can be applied externally in either a solenoid or mirror geometry. We use zerotimelag correlations of colocated density and parallel magnetic field measurements in order to study the character of MHD wave fluctuations in the plasma. Excitations are also observed in the ioncyclotron range, pointing to possible ion heating from turbulent dissipation. We intend to measure ion temperature at various beta values in order to test predictions for ion heating to scale with beta [1] and are able to vary beta between 0.1 and 10 for these purposes. These measurements were taken along with similar densitymagnetic field correlations at SSX. [1] Kunz, M. W., et al. “Astrophysical Gyrokinetics: Turbulence in PressureAnisotropic Plasmas at Ion Scales and Beyond.” Journal of Plasma Physics, vol. 84, no. 2, 2018, p. 715840201.  

CP11.00014: Current Layer Width Scaling in the Terrestrial Reconnection Experiment vs. Collisionless Simulations Samuel Greess, Jan Egedal, Adam J Stanier, Joseph R Olson, William S Daughton, Ari Le, Alexander MilletAyala, Rachel A Myers, John P Wallace, Mike Clark, Cary B Forest PIC simulations of magnetic reconnection at varying collisionality show that the outofplane current layer of the reconnection region becomes thinner and longer as the collisionality decreases [1]. While prior reconnection experiments have disagreed with this result [2], in 2017 the Terrestrial Reconnection Experiment (TREX) measured outofplane current layer widths that compared favorably with simulation results over a variety of ion species and reconnecting field strengths. Building on these findings, the 2018 run of TREX investigated similar plasmas with an improved diagnostic suite, measuring the current layers and other magnetic structures in even finer detail. In conjunction with this experimental effort, the newly developed cylindrical VPIC code from Los Alamos National Laboratory is being used to simulate the cylindrical TREX configuration. The findings from this latest experimental run and these new simulations will presented and compared. [1] Le, A. et al. JPP, 81(1). doi: 10.1017/S0022377814000907. [2] Ji, H. et al. Geophys. Res. Lett., 35, L13106. doi:10.1029/2008GL034538.  

CP11.00015: Rapid electron heating in the reconnection inflow on TREX Joseph Olson, Jan Egedal, Samuel Greess, Rachel A Myers, Alexander MilletAyala, Cary B. Forest The Terrestrial Reconnection Experiment (TREX) has been designed to study the regime of collisionless magnetic reconnection in which kinetic features such as electron pressure anisotropy develop unimpeded by collisions [1]. This fully kinetic regime is limited to Lundquist numbers of S>10ε(m_{i}/m_{e})L/d_{i}, where ε<1 is an experimental scale factor and L is the system size [2]. TREX continues to assess the presence of pressure anisotropy in experiments with S~10^{4}10^{5} in Hydrogen, well within the collisionless regime. During these events, electron heating is observed along the inflow jets from T_{e}~5 eV to T_{e}~20 eV in 1 collision time (τ_{e}~2 μs). This heating is too fast to be thermalized by collisions, and given the expected anisotropy, is likely primarily T_{e} heating. Additionally, TREX observes reconnection rates of E_{rec}~V_{A}B, much faster than the expected rate of E_{rec}~(0.1)V_{A}B, over a wide range of plasma species and experimental parameters. Current studies are looking into the relationship between the external drive and the global geometry and how these affect the kinetic structure of reconnection on TREX. [1] Egedal J. et al., Nature Phys., 8, 321 (2012). [2] Le A. et al., J. Plasma Phys., 81, 305810108 (2015).  

CP11.00016: How Alfvén waves set the largescale structure of magnetic reconnection. Harsha Gurram, Jan Egedal, William S Daughton Kinetic Alfvén waves (KAWs) has been postulated as a possible source of energy source for the aurora[1]. The simulation performed in the earlier studies were on small length and time scales, but in large simulation domain we observe that these waves do not propagate all the way into the exhaust. The simulation domain used in this study is large (200d_{i} × 30d_{i}) helping us study the nature of waves which carry the reconnection signature further downstream into the exhaust. We observe that the largescale structure or the Hall field spreads into the inflow perpendicular to the field lines due to the propagation of waves, generated at the separatrix. Near the Xline these waves have wavelengths significantly smaller than ion inertial lengths d_{i}, and hence are dispersive in nature. Away from the Xline as the wave propagates in the exhaust the wavenumber k_{} decreases, hence decreasing their propagation velocity. From the extended simulation domain, it is clear that these waves are superAlfvénic (~2V_{a0}) and dispersive near the separatrix but they become Alfvénic (1.2V_{a0}) in the exhaust. Electrons accelerated by these Alfvénic waves precipitate in the ionosphere and cause the aurora. [1] Shay M.A. et al. PRL 107, 065001 (2011)  

CP11.00017: Pressure Anisotropy Measurements on the Terrestrial Reconnection Experiment Rachel A Myers, Jan Egedal, Joseph R Olson, Samuel Greess, Alexander MilletAyala, Mike Clark, John P Wallace, Cary B Forest The Terrestrial Reconnection Experiment (TREX) at the Wisconsin Plasma Physics Laboratory (WiPPL) studies collisionless magnetic reconnection. In this regime, electron pressure anisotropy should develop, deviating from Hall reconnection dynamics and driving largescale current layer formation. This anisotropy has been seen in spacecraft such as Wind, but has not been detected easily in laboratory experiments [1]. In order to measure this anisotropy, a multidirectional Langmuir probe has been designed and constructed, containing four external tips and four shielded tips arranged evenly around the circumference of the probe shaft. Shielding and probe orientation relative to the magnetic field (measured by a 3D magnetic pickup loop) modify the currentvoltage characteristic due to differences in the number of electrons entering the probe from each direction. The changes in the IV curve thus display the extent of observed anisotropy in the collisionless reconnection region. Since the Langmuir tip radius is smaller than the Larmor radius, gyromagnetic effects can be ignored. Results and analysis from the probe are presented. [1] J. Egedal et al., Nature Phys. (2012).  

CP11.00018: Guide field influence in collisionless magnetic reconnection studies on the Terrestrial Reconnection Experiment Alexander MilletAyala, Jan Egedal, Joseph R Olson, Samuel Greess, Rachel A Myers, John P Wallace, Mike Clark, Cary B Forest Particle in cell simulations for magnetic reconnection have shown that the development and size of current sheets is dependent on the ratio of the magnetic guide field and the reconnecting magnetic field [1]. A peculiar finding of these simulations was a regime that results in elongated current sheets previously detected in Cluster spacecraft data [2]. This is explored in the Terrestrial Reconnection Experiment (TREX) which is the first laboratory that has the necessary parameters to investigate these regimes. Guide fields similar to reconnection fields will be added either by toroidal field coils or plasma guns that draw current across the device. The plasma is characterized with a new and upgraded diagnostic suite designed to have a fine spatial resolution and highresolution sampling rate. Additionally, reconnection drive coils are able to be tilted relative to the background axial field to study 3D null reconnection, where the global magnetic topology is expected to determine the reconnection dynamics. [1] Le, Ari, et al. PRL, 110. DOI: 10.1103/PhysRevLett.110.135004 [2] Phan. T.D et al. PRL 99. DOI: 10.1103/PhysRevLett.99.255002  

CP11.00019: Role of nonlinear whistler wave in reconnection site and turbulence generation. Neha Pathak, R. P. Sharma Whistler waves have ample of observations in the magnetosphere near the dayside magnetopause. Also, the role of whistler waves is well established in the context of magnetic reconnection as well as turbulence generation. In the present work, we examine the combined effect of guide field and nonlinearity in the development of turbulence in magnetic reconnection sites. We have derived the dynamical equation of 3D whistler wave propagating through Harris sheet assuming that background number density and background field are perturbed. The nonlinear dynamical equation is then solved numerically using pseudo spectral method and finite difference method. Simulation results represent the nonlinear evolution of XO field line in the presence of nonlinearity, which causes the generation of turbulence. We have also investigated the formation of current sheet/coherent structures as a result of the proposed mechanism. These localized structures have transverse scale size of the order of electron inertial length. When the system reaches quasi steady state, we have evaluated power spectrum in magnetopause, it is consistent with the THEMIS observations.  

CP11.00020: The FLARE Device and Its First Plasma Operation H. Ji, R. Cutler, G. Gettelfinger, K. Gilton, A. Goodman, F. Hoffmann, J. JaraAlmonte, T. Kozub, J. Kukon, G. Rossi, P. Sloboda, J. Yoo, The FLARE Team The FLARE device (Facility for LAboratory Reconnection Experiments; http://flare.pppl.gov) is a new laboratory experiment constructed at Princeton for the studies of magnetic reconnection in the multiple Xline regimes directly relevant to space, solar, astrophysical, and fusion plasmas, as guided by a reconnection phase diagram [Ji \& Daughton, Phys. Plasmas 18, 111207 (2011)]. The first plasma operation was successfully conducted to validate its engineering design and to demonstrate its experimental access to the parameter space of Lundquist number and normalized system size beyond its predecessor, MRX (Magnetic Reconnection eXperiment; http://mrx.pppl.gov). Details on construction completion and first plasma results will be presented; future operation plans  possibly as a user facility  and research plans will be discussed. In addition to the names listed above, The FLARE Team includes A. Bhattacharjee and S. Prager (Princeton Univ.), W. Daughton (LANL), W. Fox, M. Kalish, C. Meyers, Y. Ren, M. Yamada (PPPL), S.D. Bale (UCBerkeley), T. Carter and S. Dorfman (UCLA), J. Drake (U. Maryland), J. Egedal, J. Sarff, and J. Wallace (UWMadison).  

CP11.00021: Results from Preliminary FLARE Operation and Development of Tomographic Ion Doppler Spectroscopy Diagnostic Aaron Goodman The Facility for Laboratory Reconnection Experiments (FLARE) has been constructed with the aim of answering many longstanding problems in magnetic reconnection research. Many of these problems relate to the conversion of magnetic energy to particle energy. One of the most important diagnostics for studying the energy flow on FLARE is a measurement of spatial profiles of ion temperature. Expected ion temperatures between 530eV on FLARE make insitu measurement possible, such as those made on FLARE’s predecessor, MRX. This technique however, relies on reconstructing 2D profiles by averaging over many shots. This method is cost prohibitive and restricts studies to a single case. For this purpose, a 2D Doppler spectroscopy diagnostic is being designed that will utilize tomographic inversion to reconstruct Ion temperature profiles from measured broadening of emission lines. This presentation covers the design, numerical tests, early construction, and possible applications of the aforementioned probe as well as a brief overview of early results from first FLARE operation.  

CP11.00022: Fast Reconnection in Viscid, Partially Ionized Plasmas Jonathan JaraAlmonte, Hantao Ji, William S Daughton, Jongsoo Yoo, Masaaki Yamada, William Randolph Fox, Fulvia Pucci, Aaron Goodman Magnetic reconnection is an important physical process that results in the release of stored magnetic energy. Although commonly studied in fully ionized plasmas, many space, astrophysical, and laboratory systems are only partially ionized, and the physics of fast reconnection in these systems is not wellunderstood. Using the first fully kinetic particleincell simulations of partially ionized reconnection, the transition to fast reconnection is studied in viscid, semicollisional plasmas and found to occur when the current sheet width thins below the ioninertial length. The local reconnection rate is ionization fraction dependent, in agreement with previous experimental results, and a model for the rate is developed. In contrast, the global rate is determined by the embedding of the diffusion region within the global magnetic field and exhibits a weak dependence on system size. Additionally, we test our model for the reconnection rate by directly comparing with experimental measurements of ion and neutral flows on the Magnetic Reconnection Experiment (MRX).  

CP11.00023: High fidelity kinetic modeling of magnetic reconnection in laboratory plasmas William S Daughton, Adam J Stanier, Ari Le, Samuel Greess, Jan Egedal, Jonathan Marc JaraAlmonte, Hantao Ji Over the past decade, a great deal of progress has been made towards understanding the fast timescales of magnetic reconnection found in space and in laboratory experiments. However, a number of key questions remain, including how reconnection transitions from largescale collisional current sheets down the kinetic scales in solar flares, and the role of pressure anisotropy in the formation of extended electron current layers in the magnetosphere. Two new laboratory experiments have been built to address these respective questions – FLARE at Princeton University and TREX at the University of Wisconsin. To guide and interpret these new experiments, we have implemented a capability in the VPIC particleincell code to model these devices in realistic cylindrical geometries, including binary collisions and the coupling to the drive coils. We present initial results from the modeling of these experimental setups, along with largescale simulations of the collisionaltokinetic transition in 3D performed on Cori at NERSC. This transition differs from 2D due to the interaction of oblique fluxropes that form due to the semicollisional plasmoid instability.  

CP11.00024: The Effect of Firehose Balance on Current Sheet Formation in Asymmetric Reconnection Peter Montag, Jan Egedal, William S Daughton The data from the Magnetospheric Multiscale (MMS) mission has shed new light on the physical processes of reconnection in the magnetosphere. Although much work has been done on reconnection where the background plasma is symmetric across the layer, many of the events MMS observed had significantly asymmetric backgrounds. VPIC simulations show that in the absence of guide fields, even small asymmetries in density can create large changes in the formation of extended current sheets in the diffusion region. We propose that the differential rates of parallel heating on each side of the layer decrease its length by allowing the two sides to reach the firehose condition at different times. Including an initial temperature asymmetry in the simulations to counteract this imbalance restores the elongated current sheet, suggesting that this is indeed the mechanism behind current sheet shortening in asymmetric reconnection.  

CP11.00025: Scalings of plasmoidinstabilitymediated current sheet disruption YiMin Huang, Luca Comisso, Amitava Bhattacharjee A phenomenological model that describes the process of current sheet disruption mediated by the plasmoid instability in an evolving background has been proposed. The model incorporates the effects of the linear growth of tearing instability as well as mode stretching and advective losses due to reconnection outflow. Numerically obtained scalings of disruption conditions from the model are in good agreement with the results from direct numerical simulations [1]. In this work, we derive analytical scalings from the model in the asymptotic regime of high Lundquist number $S$. The scalings take the form of a power law multiplied by a factor that, to the leading order, is logarithmic on $S$ and the noise level of the environment. The analytic scalings agree with the predictions of previous calculations based on a principle of least time [2,3] up to the leading order expansion of the multiplication factor if the effect of outflow is neglected. Our model predicts a critical Lundquist number for disruption, which is not a constant value but weakly depends on the noise level. [1] Huang et al., ApJ 849, 75 (2017) [2] Comisso et al., PoP 23, 100702 (2016) [3] Comisso et al., ApJ 850, 142 (2017)  

CP11.00026: Characterization of Particle Energization due to Collisionless Magnetic Reconnection using FieldParticle Correlations Andrew McCubbin, Gregory Howes, Kristopher Klein Magnetic reconnection plays an important role in the energization of particles in collisionless plasmas. We apply a new fieldparticle correlation technique to explore the energization of ions and electrons in collisionless magnetic reconnection. The goal is to determine the characteristic velocityspace signatures of magnetic reconnection using singlepoint measurements of the electromagnetic fields and particle velocity distributions. Initial work has shown that in simulated magnetic reconnection, the particle energization depends strongly on the position within the reconnection geometry. This method may provide a novel means to use single point spacecraft measurements to identify particle energization by magnetic reconnection in space plasmas.  

CP11.00027: BiermannBattery reconnection in 3D colliding laserdriven plasmas Jackson Matteucci, William Fox, Amitava Bhattacharjee, Derek Schaeffer, Kai Germaschewski, Clement Moissard Recent High Energy Density plasma experiments have demonstrated magnetic reconnection between colliding plasma plumes, where the reconnecting magnetic fields were selfgenerated in the plasma by the Biermann battery effect. Using fully kinetic 3D simulations, we show the full evolution of the magnetic fields and plasma in these experiments including selfconsistent magnetic field generation about each expanding plume and where the collision of the plumes drives the formation of a current sheet. We observe fast, verticallylocalized Biermannmediated reconnection, a new, inherently 3D reconnection mechanism where the temperature profile in the current sheet coupled with the outofplane ablation density profile conspires to break inflowing field lines, reconnecting the field downstream [1]. We present a simple and general formulation to consider the relevance of Biermannmediated reconnection in general astrophysical scenarios. In addition, we investigate particle energization due to reconnection within these highly 3D systems and compare our results with those of 2D HED reconnection studies. 1) J. Matteucci, W. Fox, A. Bhattacharjee, et al., (2018) arXiv:1710.08556.
 

CP11.00028: 3D Particle Simulation of Electromagnetic Instabilities in Harris Current Sheet under Realistic Mass ratio and Finite Guide Field Zhenyu Wang, Yu Lin, Xueyi Wang, Liu Chen Previously we studied 3D instabilities in the electrostatic limit in a Harris current sheet with a finite guide magnetic field $B_G$ and a realistic mass ratio $m_i/m_e$=1836. In this work, fully electromagnetic instabilities in the Harris sheet are systematically studied by employing the gyrokinetic electron and fully kinetic ion (GeFi) particle code. Our studies show that lowerhybrid drift instability (LHDI) with $k\sqrt{\rho_i\rho_e} \sim 1$ and drift kink instability (DKI) and drift sausage instability (DSI) with $k\rho_i \sim 1$ are excited in the current sheet. The most unstable DKI is away from $\mathbf{k} \cdot \mathbf{B}=0$, and the most unstable DSI is at $\mathbf{k} \cdot \mathbf{B}=0$, where $\mathbf{k} \equiv (k_x, k_y)$, with $k_x$ being along the antiparallel field direction and $k_y$ is along the current direction. The DSI from GeFi code is consistent with fully kinetic particle simulation. On the other hand, an instability with a compressional magnetic field perturbation located at the center of current sheet is also excited under a relatively large $B_G$, and its maximum growth rate is at $\mathbf{k} \times \mathbf{B} = 0$. The presence and structure of these instabilities as a function of $B_G$ is presented.  

CP11.00029: Threedimensional hybrid simulations of spheromak merging Elena Belova Hybrid simulations with full kinetic ions and fluid electrons of counterhelicity spheromak merging have been performed using the HYM code and compared with 3D MHD simulations. The ion heating and the effects on FRC pressure profiles have been studied. In hybrid simulations the resulting FRC has larger elongation and flatter pressure profile compared to the MHD; smaller ion flow velocities before and during the reconnection have also been observed. In both cases the resulting FRC was unstable to the n=1 tilt mode, as expected for these parameters (small FLR, MHDlike regime, and small elongation). One of the unexpected results in 3D simulations was behavior of the n=1 Fourier harmonic of the ion kinetic energy, growing faster than linear, right before the reconnection. Additional simulations with varying initial separation between spheromaks have demonstrated that this behavior is related to the tilting instability of the spheromaks prior to reconnection. At closer initial separations, the growth of the tilting mode was strongly nonlinear. It has been shown that in hybrid simulations in contrast to the MHD, the reconnection rate is also very sensitive to the initial separation of two spheromaks.  

CP11.00030: The ParticleinCell and Kinetic Simulation Software Center Warren B Mori, Weiming An, Sarah Chase, Thamine Dalichaouch, Viktor K Decyk, Ricardo Fonseca, Anton Helm, Lance Hildebrand, Qiyang Hu, Archis Joglekar, Roman Lee, Fei Li, Joshua J May, Kyle Glen Miller, Adam R Tableman, Frank ShihYu Tsung, Han Wen, Benjamin J Winjum, Xinlu Xu, Yujian Zhao The UCLA ParticleinCell and Kinetic Simulation Software Center (PICKSC) aims to support an international community of PIC and plasma kinetic software developers, users, and educators; to increase the use of this software for accelerating the rate of scientific discovery; and to be a repository of knowledge and history for PIC. We discuss progress towards making available and documenting illustrative opensource software programs and distinct production programs; developing and comparing different PIC algorithms; coordinating the development of resources for the educational use of kinetic software; and the outcomes of our first sponsored OSIRIS users workshop. We also welcome input and discussion from anyone interested in using or developing kinetic software, in obtaining access to our codes, in collaborating, in sharing their own software, or in commenting on how PICKSC can better serve the community.  

CP11.00031: A New Hybrid Particle Simulation Scheme using Field Variables E & B Liu Chen, Yu Lin, Xueyi Wang, Jian Bao A gyrokinetic electron and fully kinetic ion (i.e., GeFi) particle simulation scheme was developed for problems with wave frequency up to ω<<Ω_{e}, where Ω_{e} is the electron cyclotron frequency. Such scheme is applicable for studying plasma dynamics in which the wave modes ranging from Alfven waves to lowerhybrid/whistler waves must be handled on an equal footing; such as the physics of magnetic reconnection with a finite guide field and lowerhybrid/fast mode waves in space and laboratory plasmas. In the gyrokinetic treatment, field equations are usually described by the perturbed scalar (δΦ) and vector (δA) potentials. Poisson's equations are thus needed to solve for the electromagnetic fields and may present computational challenges for nonuniform and multidimensional magnetic field geometries. Here, we present a new GeFi particle simulation scheme that employs the electric field E and magnetic field B as field variables and advances particles accordingly. The present scheme treats the displacement current selfconsistently and, thus, includes spacecharge waves. The scheme has been successfully benchmarked against the analytical linear dispersion relation in a uniform plasma.  

CP11.00032: Gyrointegrated kinetic theory for arbitrary gradient scale lengths, Larmor radii and distribution functions Olivier Izacard, Dylan P. Brennan We present a 5D electromagnetic gyrointegrated kinetic theory (GI) valid for nonMaxwellian distribution functions in magnetized plasmas with arbitrary gradient scale lengths, Larmor radii and 3D magnetic geometry. GI theory describes collective fullorbit effects and yet differs fundamentally from gyrokinetic (GK) theory in the mathematical approach to the treatment of the kinetic physics. The fundamental difference in GI is the introduction of a new "gyrointegration" that is operated on the perpendicular velocity direction of all particles at the same 5D phasespace coordinate. This gyrointegration leads to the local definition of slower 5D macroparticles without requiring any ordering on gradient scale lengths or Larmor radii. Basis sets for complete representation of the distribution function with respect to the instantaneous gyroangle are chosen to allow for the exact analytic computation of gyrointegrals of the Boltzmann equation. We then show how GI can be applied to nonMaxwellians and include arbitrary 3D magnetic geometry, and discuss how GI avoids many of the GK challenges such as the cancellation problem and the evaluation of the Ampère's law. Evaluation of conservation laws, Hamiltonian structure, and dispersion relations are discussed within the GI theory.  

CP11.00033: Spectrally Accurate Methods for Computing Kinetic Electron Plasma Wave Dynamics Jon A Wilkening, Rocky Sison, Bedros Afeyan We present two numerical methods for computing solutions of the VlasovFokkerPlanckPoisson equations that are spectrally accurate in all three variables; time, space and velocity. The first is a Chebyshev collocation method for solving the Volterra equation for the spacetime evolution of the plasma density for the linearized, collisionless case. This is then used to construct the velocity distribution function in Casevan Kampen normal modes, building on the work of Li and Spies, for example. The second is an arbitraryorder exponential time differencing scheme that makes use of the Duhamel principle to fold in the effects of collisions and nonlinearity. We investigate the emergence of a continuous spectrum in the collisionless limit and the embedding of Landau's poles in this general setting. We simultaneously resolve the effects of filamentation, phase mixing, and Landau and collisional damping to arbitrary order of accuracy. We will ultimately incorporate echoes and trapping phenomena in three dimensions by generalizing the latter method as presented here in a simpler setting.  

CP11.00034: A domaindecomposed multimodel plasma simulation of collisionless magnetic reconnection I. A. M. Datta, U. Shumlak, A. Ho, D. W. Crews Plasmas exhibit different properties depending on their degree of magnetization, charge separation, and collisionality. This implies a requirement for modeling different physics within different regimes. Work on simulation of collisionless magnetic reconnection in the past has shown that in some areas of the domain, a fluid model may provide sufficient physical accuracy while in others a kinetic model may be required, though at higher computational expense. This motivates an investigation of the collisionless magnetic reconnection phenomenon using a hybrid approach incorporating multiple models, including HallMHD, multifluid 5Nmoment, and multispecies continuum kinetics on a domaindecomposed grid in physical space. The investigations are performed using the WARPXM code developed at the University of Washington, which uses a discontinuous Galerkin RungeKutta finite element algorithm on an unstructured mesh, implementing boundary conditions between models at subdomain interfaces to couple between each model's variables. The goal of this work is to determine the parameter regimes most appropriate for each model to maintain sufficient physical fidelity over the whole domain while minimizing computational expense.  

CP11.00035: Hybrid plasma model simulations of a plasma opening switch Andrew Ho, Uri Shumlak, Iman Datta Plasma models have regimes of validity that depend on local parameters. In some problems a computationallyexpensive, highfidelity model is required in a small subset of the domain while lowercost reduced models can adequately describe the plasma behavior everywhere else. Partitioning the domain and using the simplest plasma model that is locally valid can maintain global physical fidelity while improving computational efficiency. This research investigates the coupling between MHD and twofluid plasma models using a physicsbased domaindecomposition. Comparisons are made on the accuracy and performance of using a hybrid plasma model versus a single conventional plasma model on the planar plasma opening switch. The models used are allowed to change to lower or higher fidelity models to adjust to the shifting regions of local validity as the plasma evolves. The setup consists of a low density background and a high density bulk plasma with a large density gradient, leading to instabilities which are not captured by MHD models. Elsewhere however, MHD models provide sufficient accuracy. A perpendicular magnetic field is then added to investigate changes in the plasma propagation and stability properties.  

CP11.00036: A Model on AC Contact Impedance Foivos Antoulinakis, Yue Ying Lau, Drew Packard, Peng Zhang Electrical contact is an important issue to high power microwave sources, pulsed power systems, field emitters, thin film devices and integrated circuits, and interconnects, etc. Contact resistance, and the enhanced ohmic heating that results, have been treated mostly under steady state (DC) condition. In this paper, we consider the AC contact resistance for a simple geometry [1], namely, that of two semiinfinite slab conductors of different thicknesses joint at z = 0. The conductivity of the two cylinders may assume different values. In the DC case, this model was solved exactly by Zhang and Lau [1]. We have constructed an exact solution under AC condition, and we have shown that in the limit of zero frequency, our AC solution reduces to those of Ref. [1]. New features that accompany AC condition, such as the resistive skin effect, inductive, and capacitive effects, as well as radiation losses will be explored.
[1] P. Zhang and Y. Y. Lau, J. Appl. Phys. 108, 044914 (2010).  

CP11.00037: High–Beta Relaxed Plasma Confinement in Field Reversed Configurations Wendell Horton, Philip J Morrison, Toshiki Tajima Plasmas with reversed magnetic fields and nonuniform rotational flows are ubiquitous in nature. In the MFE program these plasmas are created in FieldReversed Confinement [FRC] systems^{1} Stability conditions are derived the dynamics formulated for models of the Norman FRC machine^{2}. Cylindrical symmetric GradSharfranov^{3} plasmas p ~ B^{2}/2𝛍_{o} are derived and simulated. High beta–hot ion FRC plasmas dynamics with differential rotation expressed with Poisson brackets for four fields describing both field line bending and the FLR stabilization. The simulations produce high ion temperature deuterium plasmas with a magnetic separatrix between the closed FRC and open SOL plasmas components. ^{1}L. Schmitz, et al. Suppressed ionscale turbulence in a hot highbeta plasma, Nature Communication, 2016 [7:13860  DOI: 10.1038/ncomms13860] ^{ 2}C. Copenhaver, Axisymmetric toroidal equilibrium with plasma flow, Phys Fluids 1983. ^{3}A. J. Cerfon and P. Freidberg, Phys Plasmas 17, 032502, 2010.  

CP11.00038: Simulation of Magnetrons Using A Fast MOLT Based Implicit Astable Scheme Mathialakan Thavappiragsam, Andrew Christlieb, John Luginsland We present a novel approach for computer simulation of magnetrons using a fast, highorder, Astable implicit scheme. Since the simulator can model various structures of magnetron, it increases the physical intuition of how changes on the model effects electromagnetic behavior. The scheme works based on a MOLT formulation combined with an ADI splitting. A PDE is first discretized in time, and then the resulting boundaryvalue problems are solved using a Green's function. The integration is successively convolved using an O(N) fast algorithm. The highorder scheme is achieved by utilizing a LaxWendroff approach to exchange time derivatives with spatial derivatives. We solve magnetic vector potential A using Maxwell's equations under the Lorenz gauge, and apply PEC boundary condition using embedded boundary method. We use emitters to mimic transparent cathode and a circular source is used for solid cathode. This simulator is successfully evaluated for 2D A6 magnetron and risingsuns using pingtest and frequency analysis. Further, A6 magnetron with diffraction output (MDO) is simulated by imposing a highorder outflow boundary condition along the horn boundary and obtained Q is verified. Extension to 3D magnetrons and parallel implementation will be considered in our next work.  

CP11.00039: An energy conserving and asymptotic preserving time integrator for implicit PIC schemes Lee Ricketson, Luis Chacon Tremendous progress has been made on implicit PIC schemes in recent years. They have been shown to be more robust against the finite grid instability than their explicit counterparts. However, the classical CrankNicholson integrator on which implicit PIC is built fails to capture gradB drifts when the cyclotron frequency is not resolved. Prior modifications correct for this but break the crucial energy conservation property enjoyed by implicit PIC. We present a new time integration scheme which recovers the correct guiding center motion for arbitrary time step while retaining exact energy conservation. The resulting implicit PIC scheme holds great promise for systems in which magnetization varies widely over the spatial domain and as an alternative to gyrokinetics.  

CP11.00040: An implicit conservative electromagnetic hybrid algorithm with kinetic (particle) ions and fluid electrons Adam J Stanier, Luis Chacon, Guangye Chen The hybrid model with kinetic ions and fluid electrons is a promising approach to model multiscale problems in space and laboratory plasmas. However, current explicit schemes suffer from a number of issues related to the stable propagation of whistler waves, and finitegrid instabilities for cold ion beams [1] due to nonconservation of discrete momentum or energy. Implicit methods have been recently explored [2] to step over fast timescales, but these schemes are not conservative. Here, we present a novel particlebased nonlinear hybrid algorithm that features discrete conservation of mass, momentum and energy [3]. The scheme combines a cellcentered spatial discretization with implicitmidpoint time advance and adaptive integration of the ion orbits. A fluid momentbased preconditioner is used to accelerate convergence when stepping over fast normal modes. We demonstrate the unique conservation and stability properties of the scheme. [1] P. W. Rambo, J. Comput. Phys., 118, 152158 (1995). [2] B. Sturdevant, et. al., J. Comput. Phys., 316, 519 (2016). [3] A. Stanier, et. al., arxiv eprint:1803.07158  

CP11.00041: A fully implicit, asymptoticpreserving, semiLagrangian algorithm for the time dependent anisotropic heat transport equation. Oleksandr Koshkarov, Luis Chacon Large transport anisotropy (χ_{parallel}/χ_{perpendicular} ∼10^{10}), chaotic magnetic fields, and nonlocal heat closures make solving the electron transport equation in magnetized plasmas extremely challenging. A recently developed asymptoticpreserving semiLagrangian method^{1} overcomes this complexity by an analytical treatment of the direction parallel to the magnetic field in conjunction with modern preconditioning for perpendicular direction. In principle, the method is able to deal with arbitrary anisotropy ratios, different parallel heatflux closures, and nontrivial magnetic topologies accurately and efficiently. However, the approach was firstorder operatorsplit, and featured an accuracybased time step limitation, which can be problematic in the presence of islands, and stochastic regions. Here, we present the extension of this algorithm to allow implicit time integration. The implicit algorithm is secondorder accurate, and guarantees superior conservation and positivitypreserving properties, which were not ensured by the operatorsplit implementation. We demonstrate the merits and accuracy of the method with a two dimensional boundary layer problem, which admits an exact analytical solution. [1]  L. Chacon, et al., JCP, 272, 719, 2014  

CP11.00042: Langevinbased Coulomb collision algorithm extended for arbitrary momentum distribution in particleincell simulations Takashi Asahina, Hideo Nagatomo, Yasuhiko Sentoku Two kinds of Coulomb collision algorithms, binary collision and Langevinbased algorithms, have been actively studied, still each of them has its own advantages and disadvantages. Binary collision algorithms can handle any particle distribution functions, which is important because the fully kinetic nature is a crucial advantage of particleincell simulations. However, Langevinbased algorithms need assumptions to distribution functions or other physical quantities. This is to remove the complexity in calculating drag and diffusion coefficients of Langevin equation that states motion of particles. Theoretical background of Langevinbased algorithms has been wellestablished owing to mathematical theory of stochastic differential equations (SDE). Ordinary discretization of Langevin equation gives firstorder approximation of particle distribution. Binary collision algorithms had taken decades to be given its notsostraightforward formal proof and convergence order being 0.5 to 1.0, which is worse than Langevinbased algorithms. In this study, we developed a new Langevinbased algorithm that can handle arbitrary distribution function. Discretization technique of Langevin equation will be presented for energy and momentum conservation with the help of theory of SDE.  

CP11.00043: An integral transform technique for gyrokinetics Jeffrey Heninger, David R Hatch, Philip J Morrison The linearized VlasovPoisson system can be exactly solved using the Gtransform, an integral transform that removes the electric field term, leaving a simple advection equation. We apply this integral transform to the gyrokinetic equations. The commutator of the collision operator with the Gtransform (the ``shielding term'') is negligible and the Gtransform leaves the nonlinear perpendicularity unchanged. Since it is often useful to represent parallel velocity space in terms of Hermite polynomials, we state an explicit calculation of their Gtransform. We implement the Gtransform in a gyrokinetic code and show how it can be used to simplify the dynamics.
 

CP11.00044: Comparing Gyrokinetic Simulation Results and Linear Gyrofluid Closures to Develop Robust Closures Akash Shukla, David R Hatch, Vasil Bratanov Gyrofluid models are attractive because they provide a conceptually simpler and computationally efficient alternative to gyrokinetic models. They rely on a moment closure, which approximates the highest order fluid moment as a function of the lower order moments. Conventional gyrofluid models use linear closures designed to match the plasma dispersion function and can produce linear physics that closely matches gyrokinetics. However, these closures break down in the presence of turbulence, where the nonlinearity strongly modifies the kinetic physics. In order to develop a better understanding of the effects of nonlinear phenomena, we analyze a reduced gyrokinetic model. Detailed comparisons are made between the phase mixing in (1) the linear kinetic system, (2) the linear system closed with a HammettPerkinslike closure, and (3) the nonlinear turbulent system modeled by the DNA code. The closure predicts growth rates of the ITG mode that closely agree with the full linear kinetic system. However, the linear physics agrees with the dynamics in the nonlinear turbulent system only in very small regions of wavenumberspace. These discrepancies are analyzed in detail with the aim of formulating gyrofluid closures that are robust even in the presence of turbulence.  

CP11.00045: PlasmaPy: an open source communitydeveloped Python package for plasma physics Nicholas A. Murphy, Dominik Stańczak, Pawel M. Kozlowski, Andrew J. Leonard, Samuel J. Langendorf, Jasper P Beckers, Ritiek Malhotra, Stuart J. Mumford, Tulasi N. Parashar, Colby C. Haggerty, YiMin Huang PlasmaPy is a communitydeveloped and communitydriven open source core Python package for plasma physics. This package is being developed to provide the core functionality that is needed to support a fully open source Python ecosystem for plasma physics. PlasmaPy prioritizes code readability, consistency, and maintainability while using best practices for scientific computing such as version control, continuous integration testing, embedding documentation in code, and code review. PlasmaPy has a code of conduct and is available under a BSD 3clause license with explicit protections against software patents. PlasmaPy includes functional and objectoriented interfaces to particle data; tools to calculate plasma parameters, dielectric tensor components, and transport coefficients; mathematical functions commonly needed in plasma physics; and tools to analyze diagnostic data including Langmuir probes. Work is underway to develop PlasmaPy's base data structures. PlasmaPy's first development releases serve as an invitation to plasma students and scientists to collaboratively develop a communitywide shared software package for our field.  

CP11.00046: Comparison of VPIC Performance on Several Modern Architectures William D Nystrom, Robert F Bird, William Daughton, Fan Guo, Ari Le, Hui Li, Adam Stanier, David Stark, Lin Yin, Brian Albright VPIC [ K. J. Bowers, B. J. Albright, L. Yin, B. Bergen, and T. J. T. Kwan, Phys. Plasmas 15, 055703 (2008) ] is being ported and optimized on several modern architectures. These include KNL  

CP11.00047: Particle Simulation in Fourier Space Matthew Stephen Mitchell, Matthew T Miecnikowski, Scott Edward Parker, Gregory Beylkin The standard particleincell algorithm suffers from finite grid effects which break energy conservation, cause numerical dispersion, and create numerical instabilities. We present a gridless alternative, bypassing the deposition step and calculating each Fourier mode of the charge density directly from the particle positions. This can be done efficiently through the use of an Unequally Spaced Fast Fourier Transform (USFFT) algorithm [1,2]. After a spectral field solve, the forces on the particles are calculated via the inverse USFFT (a rapid solution of an approximate linear system). The asymptotic runtime of this approach is O(N_{p} + N_{m} log N_{m}) for each iteration, identical to the standard PIC algorithm (where N_{p} is the number of particles and N_{m} is the number of modes). We provide implementations of this algorithm and apply them to several test cases, demonstrating comparable performance and identical scaling, as well as superior energy conservation and elimination of the finite grid instability. We prove energy conservation in the continuoustime limit, as well as momentum conservation. [1] G. Beylkin, Applied and Computational Harmonic Analysis 2, 363 (1995). [2] A. Dutt and V. Rokhlin, SIAM J. Sci. Comput. 14, 1368 (1993).  

CP11.00048: Particle Method for the VlasovPoisson System Ryan Sandberg, Alexander GR Thomas, Robert Krasny We present a semiLagrangian particle method (SLPM) for the VlasovPoisson system in which the electric field is obtained by summing pairwise particle interactions rather than the usual particleincell (PIC) approach. The aim is to achieve higher accuracy and less noise than PIC, while still providing an efficient representation of phase space using an adaptive particle distribution and treecode acceleration. We compare SLPM with a standard PIC code and an Eulerian Vlasov code for several test cases.  

CP11.00049: ViscoElastic Density Functional Theory Approach to Strongly Coupled Plasmas Pierson Guthrey We seek a nonequillibrium, heterogenous, largescale model for strongly coupled plasmas. We generate a generalized hydrodynamic model for strongly coupled plasmas using density functional theory closures of BBGKY hierarchies via hypernetted chain theory. We formulate these equations in the form of a balance law, thereby providing a ``memory'' effect, facilitating correlation. This isothermal ``single fluid'' form of the electrostatic limit is modeled in a fluid context with an exact form of the functional term that is a nonlocal integral term rising out of
hypernetted chain theory. These models, dubbed the ViscoElastic Density functional (VEDF) equations, provide the first continuum models that match the dispersion of waves in
electrostatic ultracold correlated plasmas. This class of models is important because they provide a path forward that does not require a fully kinetic solution for including the
impact of long range correlation on the system. Hence these models represents a key step in being able to understand heterogeneous strongly coupled plasmas. This model, previously presented in a Molecular Dynamics (MD) framework, will be presented in a fluid framework here. We discuss the computational challenges and first steps of solving such equations.
 

CP11.00050: High Fidelity Geometry and Meshing for RF Fusion Systems Simulations Kazem Kamran, Mark S Shephard, Mark W Beall, Blair R. Downie, Saurabh Tendulkar, Rocco Nastasia Accurate RF simulations of fusion systems like ITER require the definition of high fidelity analysis geometries that include detailed antenna and reactor wall representations. The analysis domains must also include the boundaries of coupling meshes (e.g., core plasma models). The ability to effectively control the mesh generation process is enhanced by the inclusion of specific physics geometry (e.g., the SOL) into the analysis geometry. This poster will describe a set of tools being developed to support the construction and subsequent meshing of the needed analysis geometry. The steps in the process include (i) fast defeaturing of unneeded details (e.g., mounting bolts) from antenna CAD models, (ii) defining desired physics model features using input data like EFIT, (iii) combining the antenna, reactor wall, physics and any coupling meshes into a single analysis model geometry, (iv) applying simple high level mesh control to topological entities in the analysis model, and (v) executing a fully automatic mesh generator that will construct well controlled curved meshes for use in highorder finite element simulations.  

CP11.00051: Modeling the Dynamic Evolution of Weakly Collisional, NonLinear Electron Plasma Waves Laterally Confined through the Action of an Axial Magnetic Field Archis Joglekar, Richard Dwayne Sydora, Bedros Afeyan We present simulations of driven NonLinear Electron Plasma Waves (NLEPW) in the presence of collisions and laterally confined through the action of an axial magnetic field. We will treat ponderomotive forces of different lateral extent. We will compare the scaling laws in Zakharov and Karpman [1] to those modified by two dimensional effects and by the axial magnetic field. The full timedependent evolution from linear damping to nonlinear trapped states will thus be followed using a PIC code as well as VlasovFokkerPlanck models. Advantages of and potential conflicts between electrostatic and magnetic confinement of trapped electrons will be explored in the absence and presence of e  e collisions in transversely localized drive conditions as might occur in a laser hot spot. [1]: Zakharov, V. E., & Karpman, V. I. (1963). Soviet Journal of Experimental and Theoretical Physics, 16, 351–357.  

CP11.00052: Electrostatic crossfield drift instabilities in the fluid and kinetic regimes Liang Wang, Ammar Hakim, Petr Cagas, Bhuvana Srinivasan We present comparative twofluid and fully kinetic analyses of electrostatic instabilities due to crossfield drift of electrons in magnetized plasmas, particularly the electron cyclotron drift instability (ECDI). Such instabilities could induce anomalous transport in Hall thrusters, provide effective dissipation across collisionless interplanetary shocks, and disrupt current sheets during the substorm onset in the Earth's magnetosphere, etc. We first discuss connections and discrepancies between the fluid and kinetic linear theories of these instabilities under different parameter regimes. Twofluid and continuum fullykinetic Vlasov simulations are performed to further understand the instabilities, using the Gkeyll code. The simulation work will focus on both the linear and nonlinear stages of the evolution, the growth of anomalous transport, and role of turbulence and collisionless dissipation. Different parameters, particular those relevant to the X3 Hall thruster, will be used in order to investigate if such instabilities can explain anomalous transport, etc., measured in experiments.  

CP11.00053: Saturation Mechanisms of Magnetic Field Growth in a TwoStream Mediated Weibel Instability Valentin Skoutnev, Ammar Hakim We present 2X2V continuum VlasovMaxwell simulations of colliding electron populations to study the nonlinear saturation of magnetic field growth resulting from competition between TwoStream, Oblique, and Weibel modes in nonrelativistic and weakly relativistic regimes. Understanding the robustness of the Wiebel instability to other modes present is important for estimating its role in generating magnetic fields in many astrophysical scenarios with interpenetrating plasma flows. In the isotropic temperature case, we find that for hotter temperatures nonlinear saturation leads to magnetic fields with 1e2 to 1e1 of the equipartition energy density. However, for colder temperatures the nonlinear state of the Weibel instability is significantly disturbed and results in energy conversion efficiencies much lower than 1e2, an effect not observed in 1X2V simulations. Simulations of nonrelativistic counter streaming velocities with large initial anisotropic temperatures relevant to cosmological scenarios are also presented.  

CP11.00054: Kinetic simulations exploring the focusability of backward Raman amplified pulses in randomly inhomogeneous plasma Qing Jia, Nathaniel J Fisch Nearly relativistic nonfocused intensities might be reached by backward Raman amplification in plasma. Further efficient vacuum focusing to the unprecedented ultrarelativistic intensities is enabled by using a prefocused seed pulse, as it can remain wellfocused during the amplification process [1]. However, it is predicted that in an inhomogeneous plasma, the focusability might be spoiled when the amplification length is longer than a threshold [2]. Here, by using the two dimensional kinetic particleincell simulations, we examine the above defocusing effect of plasma inhomogeneities on the amplified pulse. Furthermore, to correct the phase distortions induced by the plasma density inhomogeneity, we propose to use a phase conjugated seed pulse for the amplification, with a phase front, when exiting the plasma, that enables full convergence under the vacuum focus . [1] G. M. Fraiman, N. A. Yampolsky, V. M. Malkin, and N. J. Fisch, Phys. Plasmas 9, 3617 (2002).  

CP11.00055: Rogue waves detection in ion acoustic turbulence inside a new toroidal plasma device Thiery Luc Pierre The appearance of rogue waves in turbulence has recently attracted much interest in neutral and conducting fluids. This is of major importance in nonlinear dynamics research. We propose to detect very large amplitude solitary waves in ion acoustic turbulence excited in an ionbeam plasma system. Numerical studies have been performed recently by several authors in the case of rogue waves in dusty plasmas (1,2). Our experiment is conducted in a new toroidal unmagnetized plasma device (rr= 40 cm, R=60 cm). The plasma is created by thermionic emission using hot tungsten filaments. The ionizing electrons are confined inside the torus by a multipolar magnetic structure (3) arranged in a “checkerboard” configuration of permanent magnets glued on the external wall of the toroidal vessel. Grids inserted in the plasma create the counterpropagating ion beams exciting the turbulence when the relative velocity of the ions is larger than the ion acoustic velocity. The detection of rare large events is performed in realtime using a digital storage oscilloscope. Preliminary results are presented. 1 N. Kaur et al., Plasma Sci. & Technology, 20, 074009, 2018. 2 K. He et al., Physics Letters A, 378, 2137, 2014. 3 K. N. Leung, N. Hershkowitz, K. R. MacKenzie, Phys. Fluids, 19, 1045, 1976.  

CP11.00056: Generation of THz radiation by parametric coupling of Laser and Trivelpiece–Gould mode Himani Dewan A scheme to study powerful source of radiations at Terahertz band (THz) is proposed, wherein the high power extraordinary (Xmode) laser pump parametrically decays into TrivelpieceGould (TG) mode and Kinetic Alfven Wave (KAW) in a magnetized plasma system. In this process, the nonlinear coupling between Xmode laser (ω_{0}) and TG mode produces KAW with frequency in terahertz range (THz). The Xmode laser beam exerts a ponderomotive force on the electrons, and imparts a nonlinear oscillatory velocity at beat frequency. A strong transient current is generated by the nonlinear coupling of laser velocity and TG density perturbation. The requisite phase matching condition is shown by modeling the parallelogram. High dependency upon the applied transverse magnetic field is exhibited by the efficiency, power, beam quality, and the tunability of the present scheme. At the laser intensity of 10^{16 }W/cm^{2} and magnetic field of 30 MG, the evaluated power flux, P_{THz }comes out at the Terawatt level. With the optimization of various plasma parameters, the power conversion efficiency ~ ^{ }is achieved  

CP11.00057: The modified Zakharov equations for timespace envelope in magnetoactive plasma Xiaolan Liu Considering the presence of an external magnetic field, the modified Zakharov equations are obtained with the help of twocomponent fluid mechanics and the twoscale method. Based on the nonlinear equations, the effect of the magnetic field on the modulational instability is studied. The numerical results show that the growth rate increases with the intensity of the magnetic field, which means that the magnetic field could enhance the collapse of the Langmuir field.  

CP11.00058: Diagnostic for Measuring the Ion Density Ratio in a Plasma with Two Ion Species Jeffrey S Robertson, Stephen T Vincena, Troy Carter Understanding of turbulence and transport in multiion species plasmas is important for establishing predictive capability for burning tokamak plasmas with comparable densities of D and T. In order to effectively analyze plasmas with multiple ion species, a new diagnostic is needed in order to properly characterize the individual ion species. In plasmas with two ion species, an ionion hybrid cutoff frequency exists, from which one can estimate the ratio of the two ion densities [1]. Previous work has been able to observe this cutoff frequency on a global scale [2], although a new diagnostic is needed in order to resolve local measurements. A new antenna diagnostic was developed to measure the ionion hybrid cutoff locally in the LAPD machine, and the initial results were documented and will be presented. [1] Buchsbaum, S. J. (1960), Resonance in a plasma with two ion species, Phys. Fluids, 3, 418. [2] Vincena, S. T., W. A. Farmer, J. E. Maggs, and G. J. Morales (2011), Laboratory realization of an ionion hybrid Alfvén wave resonator, Geophys. Res. Lett., 38, L11101.  

CP11.00059: Twofluid and kinetic study of sheared flow instabilities in nonuniform collisionless plasmas in ExB configurations G. V. Vogman, J. H. Hammer, W. A. Farmer The transport properties of lowdensity nonuniform ExB plasmas have important consequences in pulsed power systems such as the Z facility, where current is delivered to the load via magnetically insulated transmission lines. Formation of lowdensity plasmas within these ExB configuration transmission lines is known to give rise to parasitic currents, which interfere with load dynamics and prevent scaling of pulsed power experiments to higher energy densities. To understand the mechanisms that lead to current loss and plasma transport, the ExB environment is investigated using twofluid plasma theory and highorder continuum kinetic VlasovPoisson simulations in (x,y,vx,vy) phase space. The computational study is facilitated in part through the initialization of selfconsistent kinetic equilibria. Sheared flows are found to be present and density gradients are found to strongly influence dynamics and transport. The kinetic KelvinHelmholtz instability, induced by ExB sheared flow, is studied in detail as a candidate transport mechanism. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DEAC5207NA27344. LLNLABS753410  

CP11.00060: Experimental Investigation of Wave Generation by a Relativistic Electron Beam in Magnetized Plasma Seth Dorfman, Vadim Roytershteyn, Bart Van Compernolle, Cynthia Cattell, Gian Luca Delzanno, Bruce E Carlsten, Kimberley Nichols The interaction between relativistic electron beams and a magnetized plasma is a fundamental and practical problem that is relevant to many challenging issues in space physics and astrophysics. For example, compact highenergy electron beam sources may be used on future spacecraft to generate waves that would remove the energetic particles from the radiation belt region. Similar classes of waves (whistler, Langmuir, etc.) may also be generated by naturally occurring relativistic electron beams, possibly explaining type II/III solar radio emissions. Proposed experiments on the Large Plasma Device (LAPD) and UCLA and supporting simulations will investigate in detail the generation of waves produced by such beams, beam stability, and applicability to spacebased beams and type II/III radio bursts. Initial experiments using a 20 keV electron gun, the proposed 1 MeV experimental setup, and ongoing simulation feasibility studies will be discussed.  

CP11.00061: Two species continuum kinetic simulation of electrostatic plasma instabilities Daniel W Crews, Uri Shumlak Several classic problems in collisionless plasma kinetics are treated by solving the onedimensional multispecies VlasovPoisson system. Calculations are done using a second order discontinuous Galerkin algorithm on a high resolution structured 1D1V grid with speed and efficiency enabled by GPU parallelization. Subjects of simulation and analysis include: Landau damping and excitation of single and multispecies plasma waves, evolution of 1D plasma wave turbulence, ion interaction with electron holes, plasma streaming instabilities, collisional interaction with Landau damping, and plasma sheath kinetic effects. Some results of interest entail wavetrapped particle mixing in 1D wave turbulence and ion acoustic wave excitation by electron streaming instability. Discussion is in terms of spectral analysis and collisionless kinetic theory through the paradigms of linearized Landau damping theory, electrostatic stability, mechanical resonance in a system with mean field interaction, and the phase mixing principle. General takeaways of electrostatic plasma instability are explored such as the ideas of collisionless heating, current drive, and anomalous heat fluxes.  

CP11.00062: First results from the Bryn Mawr Magnetohydrodynamic Experiment (BMX) at the Bryn Mawr Plasma Laboratory. David A Schaffner, Carlos A Cartagena, A. Slanski, M. Shepard, F. Tamboli The first measurements from the Bryn Mawr Magnetohydrodynamic Experiment (BMX) are presented. BMX is a magnetic turbulence experiment at the Bryn Mawr Plasma Laboratory (BMPL) consisting of an ~300us long coaxial plasma gun discharge that injects magnetic helicity into a 24cm by 2m fluxconserving chamber in a process akin to sustained slowformation of spheromaks. Broadband temporal fluctuation measurements using a lowinductance magnetic pickup coil and fast Langmuir probe are reported. Mapping of gas flow using a fast ionization gauge as well as measurements of the plasma gun magnetic field structure are also reported  

CP11.00063: Magnetic Structure and Gas Dynamics Measurements of the Bryn Mawr Magnetohydrodynamic Experiment Coaxial Plasma Source Carlos A CartagenaSanchez, David A Schaffner Measurements of the magnetic structure and gas dynamics of the coaxial plasma source on the Bryn Mawr Magnetohydrodynamic Experiment (BMX) are reported. The gun consists of three pulsed magnetic coils, two outer and one inner. The coils are oriented such to generate a radial magnetic field at the mouth of the gun in order to provide a stiff, but brittle stuffing field for the ejected plasma which is necessary for sustained injection of plasma helicity. Four Parker puff valves inject pure hydrogen gas into the chamber. A fast ionization gauge is used to measure gas flow and distribution using time of flight.  

CP11.00064: Analysis of Saturation Scalings and TimeDependent Behavior in Ion Temperature Gradient Turbulence PingYu Li, Paul Willis Terry Toroidal ion temperature gradient turbulence saturates by threewave energy transfer from the instability to a stable mode through the intermediary of a zonal flow, with all three modes in the largescale instability range. Recent theory based on this mechanism derives the dependence of saturation levels for the unstable mode, stable mode, and the zonal flow on parameters like growth rate and zonal flow damping rate. This theory is tested by comparing analytic solutions of statisticalclosure energy evolution equations with numerical solutions of the primitive nonlinear twofield equations and two different approaches for numerical steady state solutions of the closure equations. To test the assumption that wavenumber dependencies are unimportant for setting levels and scalings energy evolution equations for a single triplet of wavenumbers are derived and solved. Timedependent solutions of this system allow for the study of predatorprey oscillations involving the turbulence and zonal flows that account for the first time the true saturation energy sink. Characteristic oscillation times and phasing are investigated. Dissipation, which breaks the conjugate symmetry of unstable and stable modes, is also examined to further probe saturation physics.  

CP11.00065: Experiments and Modeling of Turbulence, Transport, and Flows in a Magnetized Linear Plasma Using a Global TwoFluid Braginskii Solver Mark Gilmore, Dustin M Fisher, Ralph F Kelly, Maren W Hatch Experiments and numerical modeling of the dynamics of turbulence in the presence of flow shear are being conducted in helicon plasmas in the linear HelCat device. Modeling is being done using GBS, a 3D, global twofluid Braginskii code that solves for plasma equilibrium as well as fluctuations. Past flow measurements have been difficult to reconcile with expectations, such as azimuthal flows being dominated by Er x Bz rotation. Therefore, recent measurements have focused on understanding plasma flows, and the role of neutral dynamics. In the model, a set of driftreduced Braginskii equations are evolved using the GBS code. For lowfield Ar plasmas a crossfield thermal collisional term must be added to shift the electric potential in the ion momentum and vorticity equations, as the ions are unmagnetized. Significant radially and axially dependent neutral profiles are also included in the simulations to try and match those observed in HelCat. Simulations show a dependence on the axial magnetic field and strong axial variations that suggest drift waves may be important in the lowfield case. Recent LIF neutral profiles and offaxis plasma sourcing have been incorporated to the simulations, consistent with observations.  

CP11.00066: Liquid cooled antenna for high power helicon source Saikat Chakraborty Thakur, Russell Chakraborty Doerner, George R Tynan, Juan F Caneses, Richard H Goulding, Arnold Lumsdaine, Juergen Rapp Controlled Shear Decorrelation eXperiment (CSDX) is a helicon plasma device used to simulate scrape off layer and divertor plasmas to study turbulence, transport, helicon core formation and axial detachment. A helicon plasma source using an external antenna requires an insulating sleeve forming the vacuum boundary to allow the RF to penetrate. Recently, several highpower helicon devices have been designed [1, 2, 3], but heating issues with the RF window restrict plasma operation timescales. To mitigate this constraint, we have designed and built a novel watercooled RF window which allows steady state operation. We use deionized water as the coolant, flowing within two concentric insulators as the RF window. We have successfully demonstrated the production of steady state, high density (n_e > 10^{19} m^{3}, T_e ~ 5 eV) plasmas. We report results from several studies with and without water cooling, such as antenna loading, infrared imaging of the inner ceramic cylinder, calorimetric studies and plasma parameters from probes and spectroscopy. The results from CSDX will be used to answer critical engineering questions for the MPEX device at ORNL. [1] B. D. Blackwell, et. al., PSST, 21 055033 (2012) [2] J. Rapp, et. al., NF, 57 116001 (2017) [3] I. Furno, et. al., EPJ, 157 03014 (2017)  

CP11.00067: Characterization of a core ion mode in a linear magnetized helicon plasma device Kelly Garcia, Saikat Chakraborty Thakur, George R Tynan Controlled Shear Decorellation eXperiment (CSDX) is a RadioFrequency (RF) heated helicon plasma device used to study plasma turbulence and transport. Previous studies in CSDX show that the plasma equilibrium undergoes a self organized global transition as the magnetic field is raised above a certain threshold [1, 2]. This transition occurs simultaneously with axial plasma detachment at fixed power. At the transition, we also observe a prominent new “ion feature” at the core (r < 2 cm), which rotates in the ion diamagnetic drift direction, has very high azimuthal mode number (1015) and occurs when an ion temperature gradient develops. Based on preliminary experimental signatures, we investigate if this ion mode is due to an Ion Temperature Gradient (ITG) instability. We use linear ITG theory and CSDX experimental profiles to compute the dispersion relations and compare them with those calculated from fast camera imaging of CSDX plasmas. We also experimentally measure the parallel wavenumber of this ion mode to compare with our linear theory. Finally, our recent upgrades to CSDX (20 kW of RF power) allow us to study the ion mode independent of axial detachment. [1] S. C. Thakur et. al., Plasma Sources Science and Technology (2014) [2] L. Cui. et. al., Physics of Plasmas (2016)  

CP11.00068: Evidence for nonnegligible temperature fluctuations in a helicon plasma Adam David Light, Saikat Chakraborty Thakur, George R Tynan We present preliminary evidence for the existence of finite electron temperature fluctuations in a helicon plasma, the Controlled Shear Decorrelation Experiment (CSDX). Results indicate the presence of fluctuations with amplitude $\widetilde{T}_e/\langle T_e\rangle \sim 0.1$ in spite of a relatively flat temperature profile. CSDX is a wellcharacterized linear machine that uses a helicon antenna to produce dense plasmas relevant to the tokamak edge ($T_e \sim 3$ eV, $n_e \sim 10^{13}$/cc). Visible light from ArI and ArII line emission is collected using a fast digital camera, while floating potential and ionsaturation current are measured by an array of electrostatic probe tips. Timeaverage profiles are obtained using a compensated Langmuir probe and laserinduced fluorescence. We identify several features that indicate contributions of electron temperature fluctuations to both probe and imaging measurements. Striking radial dependence of the observed probability distribution functions (PDFs) for imaging fluctuations is explained by a simple theoretical model based on normally distributed $T_e$ fluctuations and the temperature sensitivity of the observed argon ion emission. Our results imply that particular care is needed when neglecting electron temperature fluctuations.  

CP11.00069: Investigating the effects of radial density gradient length scale on the nonlinear saturation of drift wave turbulence and zonal flow formation Boda Yuan, Eleonore Geulin, Wenbin Liu, Saikat Chakraborty Thakur, George R Tynan Controlled Shear Decorrelation eXperimental (CSDX) is a linear magnetized plasma device for drift wave (DW) turbulence and zonal flow (ZF) formation research. In addition to experiments, we shall present numerical studies of the influence of the radial density gradient length (ρ_{s}/L_{n}) on saturated DW turbulence. The simulation was carried out with BOUT++ (BOUndary Turbulence 3D 2fluid edge simulation) model of CSDX. The evolution of plasma is very sensitive to ρ_{s}/L_{n}. As ρ_{s}/L_{n} increases, there is a rapid turning on of the turbulence features along with the formation of a mean E×B shear flow (ZF). The DW turbulence enhances, gets saturated and then decreases rapidly when the ZF forms and grows. Meanwhile, the ZF behaves similarly: increases, gets saturated and then collapses, even changes sign. Experimentally, increasing the magnetic field (B) has a similar effect. Previous experiments have shown the growth, saturation and relaxation of mean E×B profiles with increasing B [1]. However, due to limited RF power, the relaxation of the profiles was also accompanied by axial detachment at high B, which is not included in the simulations. In the upgraded CDSX (with up to 20 kWatts) we can decouple the two phenomena and compare with the numerical results. [1] S. C. Thakur, PSST (2014)  

CP11.00070: An iterative wavelet method for diagnosing the onset of turbulence in magnetized plasma Ari Le, Vadim Roytershteyn, Homa Karimabadi, Adam J Stanier, Kai Schneider Recent simulations suggest that a majority of the energy dissipation on kinetic scales in turbulent magnetized plasmas may occur in thin current sheets and other localized structures (e.g. [1]). Wavelet bases naturally capture localized structures of different length scales and provide an alternative to Fourierbased methods, which are not wellsuited for these purposes. Here, we apply an iterative wavelet technique, originally formulated for neutral fluid turbulence (e.g., [2]), to extract and characterize coherent features in the plasma current density in simulations of KelvinHelmholtz unstable flowshear layers conducted using several models (fully kinetic, hybrid kinetic ion/fluid electron, and Hall MHD). The onset of turbulence is identified with the growth of a background of incoherent fluctuations spread across a range of scales. We compare and demonstrate advantages of this technique against widely used diagnostics of turbulence such as the appearance of nonGaussian statistics and Fourier spectra, among others.  

CP11.00071: Mean Bfield Effects on Jet Formation in the βPlane Magnetohydrodynamics Turbulence in the Solar Tachocline ChangChun Chen, Patrick Henry Diamond
The dynamics of solar tachocline is of importance in the solar magnetic activity; the underlying physics of tachocline dynamics, however, remains unclear. Studies of tachocline have shown that the nonlinear interaction of Rossby waves— a process of inhomogeneous mixing of potential vorticity (PV)— forms a zonal jet, while a mean toroidal magnetic field (Bfield) suppresses the zonal flow with a critical parameter proportional to B^{2}/η, where η is the magnetic diffusivity (Tobias et al. 2007). Thus, the role of toroidal Bfield is of significance in turbulence properties of the tachocline. As a simple model of an incompressible and stably stratified tachocline, we consider a rotating, twodimensional model— βplane— and examine the effect of a mean Bfield on the PV mixing in the βplane turbulence. We report an analytical theory of jet suppression due to the mean Bfield, which also enters as a modification of the cross phase in the vorticity flux, and as an initiator for a flow along the tiled field lines. A mean field equation for the vorticity and comparisons of realspace and kspace formulations will also be presented by using closure and quasilinear approximations.  

CP11.00072: Power accounting of plasma discharges in the linear device ProtoMPEX Melissa A Showers, Pawel Piotrowicz, Clyde J Beers, Theodore Mathias Biewer, Juan F Caneses, John Canik, John B Caughman, David C Donovan, Richard H Goulding, Arnold Lumsdaine, Nischal Kafle, Juergen Rapp, Holly Ray ProtoMPEX is a prototype device whose primary purpose is to develop the plasma heating source concepts for the Material Plasma Exposure eXperiment (MPEX), a steadystate linear device being developed to study plasma material interactions (PMI). A multiregion power accounting study of ProtoMPEX was performed utilizing expanded diagnostic measurements and improved modeling to identify mechanisms and locations of heat loss from the main plasma. Regions with lower power transport efficiencies have been identified. Powertotarget plate efficiencies have been calculated for a variety of plasma production scenarios: helicon power only, helicon power supplemented with electron cyclotron heating (ECH), helicon power supplemented with ion cyclotron heating (ICH), and helicon power supplemented with combined ECH and ICH. These efficiencies are extrapolated to MPEX relevant applied power sources in order to estimate the heat fluxes expected to be deposited to target plate surfaces for future steadystate PMI studies. Areas requiring further diagnostic measurements and modeling are identified.  

CP11.00073: Effects of magnetic mirror on helicon plasma transport in ProtoMPEX Nischal Kafle, Juan F Caneses, Theodore Mathias Biewer, John B Caughman, Richard H Goulding, Melissa A Showers, Jeremy Lore, Donald Spong, David C Donovan The Prototype Material Plasma Exposure eXperiment (ProtoMPEX), a linear device, at ORNL has a helicon plasma source with additional microwave electron heating and RF ion heating. ProtoMPEX has several magnetic mirrors which could affect the plasma transport. For example, the magnetic field near the helicon source is ~0.07T, and the peak magnetic field in the central chamber is ~1.0T; creating a large magnetic well. In contrast, the magnetic field at the target region is variable, but typically <0.5T. This study is focused on the transport of the helicon generated plasma in the presence of various magnetic mirrors. Experiments have been conducted keeping the helicon source region magnetic field constant and lowering the peak magnetic field downstream towards the target. Results showed expansion and compression of the magnetic field lines which affected the electron density and plasma flow velocity along the magnetic flux tube, but the total ion flux reaching the target was conserved. These experiments revealed that the thermal plasma, streaming along the magnetic field lines in ProtoMPEX behaves like a compressible fluid. Detailed analysis from various diagnostics will be presented and compared to modeling.  

CP11.00074: Development of a Twophoton Absorption Laser Induced Fluorescence Diagnostic for ProtoMPEX Thomas E. Steinberger, Theodore M. Biewer, Juan F. Caneses, Juergen Rapp, Earl E. Scime Twophoton laser induced fluorescence (TALIF) provides a nonperturbative method to directly measure mean bulk flow, temperature, and absolute densities of neutral deuterium in fusionlike plasmas. Implementation of TALIF on the Prototype Material Plasma Exposure eXperiment (ProtoMPEX) produces several technical challenges to overcome. First, probing neutral deuterium requires high intensity, VUV light creating significant difficulties for transmitting laser light through a beam path and standard vacuum windows. Second, limited optical access complicates designs for TALIF injection and collection optics. Lastly, absolute density measurements require calibration, usually using krypton or xenon gas. We present designs for beamline path, confocal injection optics, and shottoshot calibration to address each challenge. TALIF will be used to measure neutral deuterium densities, temperatures, and flows in the helicon source region and ultimately in front of a target exposed to fusionlike conditions.  

CP11.00075: Development of a HELIOS Diagnostic for the Prototype Material Plasma Exposure eXperiment Holly Ray, Theodore Mathias Biewer, Juan F Caneses, Nischal Kafle, Jorge Manuel Munoz Burgos, Ezekial Unterberg, Oliver Schmitz A new helium lineratio spectral monitoring (HELIOS) diagnostic is being implemented on Oak Ridge National Laboratory’s (ORNL) Prototype Material Plasma Exposure eXperiment (ProtoMPEX). The HELIOS diagnostic is constructed so that the puffed He gas outlet is as close to the plasma column as possible. Fiber optics transfer the light emission from the plasma to a Filterscope system where the intensity is measured at a sampling rate of 100 kHz for three separate helium lines: 667.9 nm, 706.53 nm, and 728.0 nm. The open magnetic geometry of ProtoMPEX allows for the comparison of the HELIOS derived n_{e} and T_{e }values to nearby double Langmuir probes (DLP) and Thomson scattering (TS) measurements. The HELIOS system (100 kHz) should provide n_{e} and T_{e} at much higher rates than either the DLP (200 Hz) or TS (10 Hz). HELIOS measurements, however, are complicated by lineofsight integration issues and the low temperature of ProtoMPEX require collisional radiative model (CRM) calculations to be extended beyond the range traditionally used in previous tokamak measurements. Preliminary HELIOS measurements give edge T_{e} values of 5  8 eV and edge density values of 3e18 m^{3} – 6e18 m^{3}. This work was supported by the US. D.O.E. contract DEAC0500OR22725 and DESC00013911.  

CP11.00076: Status of DualLaser Digital Holography for Surface Characterization at ORNL C. D. Smith, T. M. Biewer, C. E. Thomas, C. J. Beers, Z. Zhang A duallaser differential digital holography system is under development at Oak Ridge National Laboratory (ORNL) for 3D measurement of surface erosion of plasma facing component (PFC) materials. Digital holography produces topological data of a target from IR laser interferometry. The system is capable of a depth resolution range perpendicular to the surface of 100 nm to 4.5 μm (singlelaser holography) and up to 2 mm for duallaser differential holography. Transverse resolution of the measurements is limited by diffraction effects, covering an area of 7x7 mm^{2} with a 1X magnification lens. Holograms produced “on the bench” of test targets have shown that the system can produce measurements from <1 μm to ~2 mm total depth, demonstrating good progress towards deployment in the field. Measurements of ProtoMPEX plasmaexposed targets, including a SiC target, have been made. Status of the duallaser system and progress in single and duallaser measurements will be presented.  

CP11.00077: Tungsten sputtering by simultaneous deuterium and nitrogen irradiation Masatomo Yamamoto, Heun Tae Lee, Kenzo Ibano, Yoshio Ueda In magnetic fusion devices, extrinsic impurities like nitrogen (N) are introduced in hydrogen plasmas to reduce the power load onto tungsten (W) plasma facing components. Evaluating the sputter characteristics of W under simultaneous irradiation of hydrogen isotopes and nitrogen species is required to quantify the effects of Wcontamination on plasma confinement. Due to the rich chemistry involving hydrogen and nitrogen species, the W surface is expected to evolve in a complex manner with significant influence on the W sputtering. In this study, we report on systematic W sputtering experiments as a function of incident ion energy (3001000 eV) and sample temperature (400700 K) for fixed D/N ratio (3.5% N). Experimental Wsputtering yields are compared to the results of a dynamic BCA code (TRIDYN). In the energy range between 7001000 eV, experiments and simulation results agree within 20% as a function of incident ion energy, with very weak dependence on temperature. However, in the energy range between 300500 eV, sputtering yields show stronger temperature dependence. Therefore, we conclude that physical sputtering is the dominant mechanism at incident energy greater than 700 eV, while deposited nitrogen is desorbed by chemical sputtering at incident energy less than 500 eV.  

CP11.00078: Simulation of Tungsten Erosion and Migration in the ITER Divertor as Part of an Integrated Model for PSI Tim Younkin, John Canik, Mark R Cianciosa, Philip C Roth, Ane Lasa, Davide Curreli, Jon T Drobny, Sophie Blondel, Brian Wirth, Wael Elwasif, David L Green A new simulation capability has been developed to simulate the coupled interaction of the plasma and surfaces in fusion devices. The integrated model includes a wide range of phenomena, including models for a) the scrapeoff layer plasma including fuel ions and extrinsic impurities (using SOLPS[1]), b) transport and redeposition of eroded wall material (using the newly developed Monte Carlo code GITR[2]), c) the implantation of plasma ions into the material and subsequent wall erosion (using FTRIDYN,[3]), and d) the dynamics of the subsurface. These components have been combined to predict the evolution of surface morphology, recycling and retention, and the impact of erosion and redeposition on these processes. After benchmarking against PISCES experiments, we have now applied this model to make predictions to the ITER divertor. Predictions for standard and helium operations, and for a partially and completely detached divertor, will be presented. Modeling results presented focus on the input data for the impurity transport simulation and their impact on impurity migration in the ITER divertor. [1] R. Schneider et al, Contrib. Plasma Phys. 46 (2006) 3. [2] GITR Github repository, https://github.com/ORNLFusion/GITR [3] J. Drobny, J. Nucl. Mat. 494 278283 (2017)  

CP11.00079: Density Estimation Techniques for Multiscale Coupling of Kinetic Models of the Plasma Material Interface Shane Keniley, Davide Curreli We analyze two classes of DensityEstimation techniques which can be used to consistently couple kinetic models of the plasmamaterial interface, intended as the region of plasma immediately interacting with the first surface layers of a material wall. In particular, we handle the general problem of interfacing a continuum multispecies VlasovPoissonBGK plasma model to discrete surface erosion models. The continuum model solves for the energyangle distributions of the particles striking the surface, which are then driving surface response. A modification to the classical BinaryCollision Approximation method is utilized as a prototype discrete model of the surface, to provide boundary conditions and impurity distributions representative of the material behavior during plasma irradiation. The numerical tests revealed superior convergence properties of Kernel Density Estimation methods over Gaussian Mixture Models, with EpanechnikovKDEs being up to two orders of magnitude faster than GaussianKDEs. The methodology presented allows a selfconsistent treatment of the dynamic response of the surface including effects such as sputtering, backscattering, and ion implantation.  

CP11.00080: Flow Collisionality Effects in Plasma Guns for Simulating Fusion Wall Response to Disruption Events Thomas C Underwood, Vivek Subramaniam, William Riedel, Mark A Cappelli, Laxminarayan L Raja In this work, the suitability of a pulsed coaxial deflagration accelerator to simulate the interaction of edgelocalized modes with plasma first wall materials is investigated. Suites of experimental diagnostics are used to characterize plume conditions in the Stanford plasma gun facility to quantify both the incident plasma heat flux and estimate the mean free path in the vicinity of stagnating surfaces. The process by which plasma jets stagnate on tungsten tokens is visualized using an ultrahigh frame rate CMOS camera coupled to a Ztype laser Schlieren apparatus. Results indicate the formation of a strong extended bow shock that acts to redirect the flow away from the surface of the material. Measurements show that while sufficiently high plasma heat fluxes are achievable with gun devices (in excess of 10 GW m2), significant differences in plasma density and temperature cause the formation of collisional fluid shocks that are not expected at similar timescales during ELM events in fusion conditions. Finally, MHD simulations are employed to quantify the shock shielding effect within the flow and how the strength of the diversion varies as the energy of impeding plasma jet changes.  

CP11.00081: Comparative Study of Explicit vs. Implicit ParticleinCell schemes for Plasma Sheath Simulations Davide Curreli, Jon T Drobny, Rinat Khaziev In this work we present a comparative study of explicit vs. implicit fullykinetic fullorbit ParticleinCell schemes, using: (1) the explicit VlasovPoisson scheme of the hPIC[1] code, and (2) the implicit MaxwellVlasov scheme of Chacon et al.[2]. Implicit schemes remain stable at much longer time steps than traditional, explicit schemes, but at greater computational cost. The MaxwellVlasov formulation avoids the use of a Poisson solver by directly evolving the electric field in time based on the particle fluxes. We report simulation results of asymmetric phasespaces (e.g. bumpontail instability) and finitesize domains (nonperiodic) facing an absorbing wall, where a plasma sheath is formed. [1] Khaziev, Curreli, Comput. Phys. Commun. 229, 87, 2018; [2] Chacon, Chen, Barnes, J. Comp. Phys. 233, 1–9, 2013.  

CP11.00082: Latest developments in BOUT++ boundary plasma turbulent transport simulations X.Q. Xu, Zeyu Li, Nami Li, C.K Sun, Libo Wang, Y.M. Wang, Ben Zhu A significant progress has been made recently in BOUT++ simulations. The results will be summarized here including, but not limited to: (1) Developed simulation models for density limited disruptions and the resulting scrapeoflayer broadening. (2) Derived a Landau fluid closure for arbitrary frequency, implemented and tested in BOUT++ simulations. (3) Performed linear analyses of peelingballooning modes in high beta pedestal plasmas. Taking the kinetic effects into account, simulations of kinetic peelingballooning mode show the existence of the high beta peelingballooning mode stability region. (4) Simulated the ELMs triggering by lithium pellet and its ablation process. Both BOUT++ turbulence and transport codes are used to simulate the divertor heat flux width, which is consistent with experimental Eich scaling for current tokamaks. However, transport simulations show that (1) Drifts and turbulence are locked in a tight competition for CMod and a critical SOL transport coefficient is found. (2) ITER & CFETR will possibly operate in a turbulence dominant regime with a heat flux width larger than those extrapolated from the Eich scaling and Goldston HD model sets the lower limit of the width.  

CP11.00083: Multitimescale coupling simulation between turbulence and transport codes using BOUT++ framework N. M. Li, X. Q. Xu, T. Y. Xia, J. Z. Sun, D. Z. Wang A new coupling model has been developed to integrate multiscale turbulence and transport simulations, such as ELM bursts and pedestal recovery. As a proof of principle, we first start from a set of threefield twofluid model equations which includes the pressure, current, and vorticity. The equations are separated into the slowly evolving part of the axisymmetric component by taking a time average of the axisymmetric component. The timeaveraged fluxes, which are quadratic in fluctuating quantities, act as drive terms for the timeaveraged axisymmetric quantities that determine the plasma transport, and therefore the largescale evolution of the plasma profiles. Good agreement has been achieved for the solutions obtained by the coupled simulation to direct numerical simulation of the unseparated equations. Multiple ELM cycles have been simulated using the coupling technique in the circular geometry. The axisymmetric component evolution tracks the pedestal pressure profile collapsing in the fast component and the profile recovery between ELMs with additional sources in the slow component. The same coupling technique is applied to a set of sixfield twofluid model equations and results will presented.  

CP11.00084: Linear Analyses of Peelingballooning Modes in Highbeta Pedestal Plasmas Chuankui Sun, Xueqiao Xu, Bo Li, Pengfei Li We present the 3D linear simulations of edge plasma instabilities using the 3field peelingballooning model and gyroLandaufluid (GLF) model under the BOUT++ framework. A series of realistic equilibria are generated by a global equilibrium solver CORSICA, where the Shafranov shift, elongation effects and bootstrap current are included. Simulations of ideal ballooning modes show that it reaches the second stability region locally, but not globally because of the distribution of shear and α. With the diamagnetic effects and current drive included, the simulation results of peelingballooning modes (PBM) using the reduced fluid model show that the unstable region of PBM in highbeta cases decreases in both beta and toroidal mode number. The bootstrap current destabilizes the PBM in lowbeta cases, but stabilizes the highn modes in the highbeta cases. The simulations with different fractions of bootstrap current indicate a trend for the existence of the high beta peelingballooning mode stability region. Taking the kinetic effects into account, linear simulations of kinetic peelingballooning mode using the GLF model show that this region can be accessed, with the highbeta, lown modes stabilized.  

CP11.00085: Impact of Edge Current on ELM Energy Loss Using BOUT++ Zeyu Li, X.Q. Xu, H. Seto, M. YAGI, V.S. Chan Investigation on the edge current effect on Edgelocalizedmode (ELM) energy loss is carried out by using BOUT++ 4field module with zonal ExB flow and zonal magnetic flux perturbation. A set of JET like equilibriums with different edge current are generated selfconsistently using CORSICA while keeping the plasma shape, total stored energy fixed. Surprisingly, we found that the linear growth rate of peelingballooning mode decreases when edge current increases, which showed that the local magnetic shear stabilize effect should be taken into consideration. Same trend is found in the linear phase of nonlinear simulation, meanwhile the final saturated energy loss fraction does not show a simple linear dependence. Similar phenomenon is found in both low and high collisionality cases. Zonal ExB flow shows an important role in keeping perturbation from spreading inward and results in a following “LH” transition around peak gradient region. This study tends to shed the light to derive a small ELM energy loss operation scenario for future machines, such as ITER and CFETR, by using edge current control system.  

CP11.00086: Simulation of divertor heat flux widths on EAST by BOUT++ transport code G.Z. Deng, X.Q. Xu, N.M. Li, L. Wang, X.J. Liu, T.Y. Xia, X. Gao The BOUT++ edge plasma transport code is applied to study the effects of drifts and neutral on the divertor heat flux widths of EAST steady state Hmode discharges. The heat flux widths from the simulations are in reasonable agreement with the experiments, however, the widths from both the simulations and experiments turn out to be a factor of 2 larger than Goldston’s driftbased model and Eich’s multimachine scaling, which may probably be due to the dominant RF heating on the EAST discharges involved in this work. Drifts are found to have dramatically increased both the heat flux and its width. Neutral seems to have increased the density and temperature gradient at the divertor region, which makes the heat flux increased by a factor of about 4.4 while the heat flux width decreased by about 26%. Detailed analysis about the effects of drifts and neutral will be presented. Further simulation on EAST NB heated Hmode discharges will be carried out and included in this work to figure out the heating scheme effects on divertor heat flux width.  

CP11.00087: A gyrokinetic model for the tokamak periphery Rogerio Jorge, Baptiste Frei, Paolo Ricci, Nuno F Loureiro, Sonia Gamba, Lorenzo Perrone, Konovets Vyacheslav Despite significant development over the last decades, a model able to describe the tokamak periphery region extending from the edge to the far scrapeoff layer is still missing. In this work, we present a new gyrokinetic model that retains the fundamental elements of the plasma dynamics at the tokamak periphery, namely electromagnetic fluctuations at all scales, comparable amplitudes of background and fluctuating components, and a large range of collisionality regimes. Such model is derived within a gyrokinetic fullF approach, describing distribution functions arbitrarily far from equilibrium, and projecting the gyrokinetic equation onto a HermiteLaguerre velocity space polynomial basis, obtaining a gyrokinetic moment hierarchy. This extends a previously derived electrostatic driftkinetic moment hierarchy to the electromagnetic gyrokinetic regime. The treatment of arbitrary colisionalities is performed by expressing the full Coulomb collision operator in gyrocentre phase space coordinates, and providing a closed formula for its gyroaverage in terms of the gyrokinetic moments. In the electrostatic high collisionality regime, the novel hierarchy reduces to an improved set of driftreduced Braginskii equations which have been widely used in scrapeoff layer simulations.  

CP11.00088: Kinetic treatment of ions in the magnetic presheath Alessandro Geraldini, Felix I ParraDiaz, Fulvio Militello The magnetic presheath is a quasineutral boundary layer, extending a few typical ion Larmor radii from the wall, in which ions may intersect the wall during a gyroorbit [1]. It is present if the magnetic field makes an oblique angle with the wall. Due to the large size and distortion of the ion gyroorbits, a kinetic treatment is necessary to obtain the electrostatic potential across the magnetic presheath. When the angle between magnetic field and wall is small, the ion distribution function is approximately constant when expressed in terms of appropriate quantities [2]. Hence, the ion density can be obtained [3]. The electron density is assumed to be a Boltzmann distribution. Using an iteration scheme to solve the quasineutrality equation gives the electrostatic potential across the magnetic presheath [4]. The ion distribution function entering the Debye sheath is obtained, and the dependence on ion temperature and angle is studied. References:  

CP11.00089: Reduced model (nSOLT) simulations of neutralplasma interaction in the edge and SOL: verification, equilibrium profiles and turbulent momentum transport D. A. Russell, J. R. Myra, D. P. Stotler The 2D scrapeofflayer turbulence code (SOLT) has been extended to include neutralplasma interactions (nSOLT). A Boltzmann equation describes the evolution of the binormally (y) averaged neutral distribution function, G(x,v_{x},t), in the radial dimension. Neutralplasma interactions are mediated by chargeexchange and ionization rates based on poloidallyaveraged plasma density and temperature. As a verification exercise, equilibrium neutral density profiles from nSOLT simulations and from the Monte Carlo neutral transport code DEGAS 2 are compared, for timeaveraged NSTX Hmode plasma profiles, and are found to be in good agreement. nSOLT simulations that evolve the plasma in 1D, using radial diffusion as a proxy for turbulent (blob) transport, illustrate the convergence to selfconsistent neutralplasma equilibria sustained by a neutral source in the farSOL and plasma heating in the core. In 2D nSOLT turbulence simulations, the effect of neutral friction on the radial transport of injected poloidal plasma momentum is studied. Neutral friction and plasma cooling are compared as modifiers of the plasma flows.  

CP11.00090: Physics Designs for a Lithium Vapor Box Test at PPPL and a Lithium Vapor Detachment Experiment at MagnumPSI J. A. Schwartz, K. R. Butler, E. D Emdee, M. A. Jaworski, R. J. Goldston The lithium vapor box [1] is under study as a candidate divertor. Prior to implementation in a tokamak, the concept should be tested with labscale experiments and in linear plasma devices. Key physics issues to be evaluated include the efflux of Li vapor (1a) without and (1b) with plasma, (2) the required density of vapor to induce detachment and volumetric recombination, (3) power spreading away from the target during volumetric recombination, (4) transport of Li ions in the plasma, and (5) pumping of H (and potentially He) emitted by a detaching plasma, using codeposition onto liquid Li surfaces. An experiment at PPPL to test (1a) is being constructed, and the physics design for an experiment at the linear plasma device MagnumPSI is being developed with the primary goals of measuring (1b), (2), (3), and potentially (4). We will present the physics designs of these experiments, including both practical aspects [see also Butler et al, this conference] as well as a simplified plasma model that can be adjusted to study the implications of a range of assumptions.  

CP11.00091: Turbulence Characteristics from XGC1 simulations of Tokamak Edge. Ioannis Keramidas Charidakos, James Richard Myra, Scott Edward Parker, SeungHoe Ku, Randy Michael Churchill, Robert Hager, ChoongSeock Chang Strong turbulence near the separatrix is believed to produce filamentary structures (blobs) whose detachment from the bulk impacts the heat flux width and, as a result, the total power deposited at the divertor. Although considerable progress has been made in core research, studies of the edge so far have been mostly confined to reduced models and simplified geometries.  

CP11.00092: Introduction of kinetic effects to fluid simulation by a particle model Akito Tanaka, Kenzo Ibano, Mayuko Obiki, Tomonori Takizuka, Heun Tae Lee, Yoshio Ueda, Nobuhiko Hayashi, Kazuo Hoshino Fluid simulations are mainly used for SOL/divertor plasma modeling, but there are some discrepancies between simulated and experimental results. It is thought that one of the reasons is that fluid simulations cannot sufficiently treat kinetic effects. Particularly, in edge plasma when collisionality is weak, the velocity distributions of electrons and ions are distorted from Maxwellian distribution, and kinetic effects become important. Then, in this study, we have tried to introduce kinetic effects to fluid simulation by combining with particle simulation. The particle simulation can correctly treat kinetic effects in the nonMaxwellian region, but it is difficult to apply the particle simulation to a large system and in a long time scale due to its high cost. In order to overcome this obstacle, we do not calculate the selfconsistent electric field but just adopt the sheath boundary condition model. Plasma parameters obtained by a fluid simulation are converted into velocity distributions for electrons and ions, and these data are taken as initial values of particles. By calculating the trajectories considering collision for a short time scale, we have successfully introduced the particle simulation results, which correctly consider kinetic effects, into the fluid simulation.  

CP11.00093: Overview of the EUROfusion Medium Size Tokamak scientific program Antti Hakola, Matthias Bernert, Tommaso Bolzonella, Stefano Coda, Hendrik Meyer Under the EUROfusion MST1 program, coordinated experiments and related analysis and modelling tasks are carried out at three European medium sized tokamaks (ASDEX Upgrade, TCV and MASTU), thus complementing the JET program for preparing a safe and efficient operation for ITER and DEMO. Work under MST1 benefits from crossmachine comparisons but also makes use of the unique capabilities of each device. For the 2017/2018 campaign 24 topical areas were defined targeting the three main objectives: Development towards an edge and wall compatible Hmode scenario with small or no ELMs Characterization of conventional and alternative divertor configurations for ITER and DEMO Development and characterization of methods to predict and avoid disruptions as well as control and mitigate runaway electrons. This contribution will give an overview of the work done under MST1, highlighted by key results for each of the main objectives. These include suppression of ELMs by applying magnetic perturbations and assessing their influence on divertor heat loads, recent advances in accessing the ELMfree Imode regime, detailed characterization of SOL transport and detachment in different divertor configurations, and development of new tools to control runaway electron beams.  

CP11.00094: Runaway electron mitigation by applied magnetic perturbations in the ASDEX Upgrade and COMPASS experiments Marco Gobbin, Ondrej Ficker, L. Li, Y. Liu, E. Macusova, T. Markovic, Massimo Nocente, Gergely Papp, A. Casolari, N. Lamas, Lionello Marrelli, Jan Mlynar, G. Pautasso, Paolo Piovesan, M. Teschke, Wolfgang Suttrop, M. Valisa, the ASDEX Upgrade Team, the COMPASS team, the EUROfusion MST1 Team Runaway electrons (RE) generated during tokamak disruptions represent a severe threat for plasmafacing components in controlled fusion devices and require reliable and efficient mitigation techniques. Dedicated experiments and modeling have been carried out by considering resonant magnetic perturbations (RMP) of different amplitude with toroidal mode number n=1 in ASDEX Upgrade [1] and with n=1 and n=2 in COMPASS. The application of RMPs results in a lower amount and shorter duration of the postdisruption runaway electron current. The efficacy of this technique strongly depends on the uppertolower coil phasing i.e on the poloidal spectrum of the perturbations which has been reconstructed including the plasma response by the code MARSF [2]. Most performant RMPs in RE mitigation partially affect also the electron temperature, the disruption evolution and the associated hardXray spectrum. [1] M.Gobbin et al, Plasma Phys. Control. Fusion 60 014036 (2018)  

CP11.00095: Disruptivity and Density Limits in MAST and other Tokamaks John William Berkery, Steven Anthony Sabbagh, Andrew Thornton, Andrew Kirk, Lucy Kogan, Jonathan Hollocombe The Disruption Event Characterization and Forecasting (DECAF) code was written to automate analysis of tokamak data for disruptivity characterization of existing databases and related testing of specific physics analyses for disruption forecasting, such as density limits. DECAF analysis has been performed on the MAST, KSTAR, NSTX, NSTXU, and TCV devices. DECAF is equipped to produce event probability plots of events leading to the disruption identified by DECAF physics models, such as MHD modes, nowall beta limits, or the current quench itself. It was found that low q_{95} was especially disruptive for MAST, as was density above the Greenwald limit. Recently a local island power balance limit theory, developed to explain the observed density limit in tokamaks, has been implemented in DECAF and tested on a set of NSTX discharges with long periods of rising density, eventual onset of low frequency n = 1 MHD activity, and disruption. Both the local island and global Greenwald limit criteria were found to rise towards, or surpass theoretical limits associated with the termination of the discharges. Both criteria are being evaluated for their utility as disruption predictors for the MASTU device.  

CP11.00096: The role of gas injection and magnetic perturbations in Runaway Electron experiments at COMPASS tokamak Jan Mlynar, Ondrej Ficker, Eva Macusova, the COMPASS Team, the EUROfusion MST1 Team Since 2014 the COMPASS tokamak has been contributing to the Runaway Electron (RE) research programme coordinated by the EUROfusion consortium, which is focused on methods of RE mitigation linked to potential threat of the wall damage in tokamaks due to RE beams. The recent experimental campaigns at COMPASS were dedicated to experiments with Massive Gas Injection / gas puff and with the Resonant Magnetic Perturbation fields which are relatively strong in COMPASS, B_RMP / B_T ~ 1%. For the decay studies, scenario with zero loop voltage was implemented. The results enhanced understanding of the role of the B_T, the injected gas amount or the RE seed. Experiments with RMP confirmed that the best RE mitigation is associated to strong resonant component with core kink response.
 

CP11.00097: Low recycling regime with 25 MW/20 s fusion power at 4 MW/120 keV NBI with Q_DT > 6 for JET DT experiment Leonid Zakharov In 1997, 16 MW of fusion power with fusion efficiency factor Q_DT=0.6 was demonstrated in DT experiment on JET tokamak for a fraction of second. Also, 6 MW of fusion power was produced for 5 s with efficiency Q_DT=0.25. The incoming DT experiment on JET has a  

CP11.00098: Subdivertor fuel isotopic content detection limit for JETDTE operation C. Christopher Klepper, Stephane Vartanian, Bernard Pegourie, David Douai, Ephrem Delabie, Ionut Jepu, Uron Kruezi In preparation for JET DeuteriumTritium Experiment 2 (DTE2, ca. late 2019) the detection limit capability for fuel isotope concentrations in JET the subdivertor region has been studied based on a reexamination of the DTE1 Penning optical spectroscopy data [1, 2]. The analysis indicated a 1% T/(H+D+T) lower limit, which is considered sufficient for DT operation, while detection down to <~1% concentrations is desired for neutron budget control during TT operation and during DD (following DT). In support of this study, an advanced spectral fitting program at IRFM CEA, with full error statistics capability, has been operated in simulation mode, successfully simulating the error that was exhibited in the DTE1 data. This detection limit degrades over time due to attenuation of Penning sourceemitted light by sourceproduced thin film deposition. An upgraded diagnostic for DTE2 is aiming to reduce light losses, partly by mitigating window coatings is being completed in time for this critical for JETDTE2 measurement and likely the principal way to diagnose lowlevel fuel isotopic concentration in ITER plasmas [2]. [1] D.L. Hillis et al., RSI 70,1999 [2] C.C. Klepper et al., 2017 JINST 12 C10012  

CP11.00099: Kinetic Equilibrium Reconstruction and Stability Analysis of KSTAR Plasmas Supporting Disruption Event Characterization and Forecasting Yanzheng Jiang, Steven Sabbagh, YoungSeok Park, John Berkery, JaeHeon Ahn, Juan Riquezes, JinSeok Ko, JongHua Lee, SiWoo Yoon, Alan Glasser, Zhirui Wang High fidelity kinetic equilibrium reconstructions are an essential requirement for accurate stability and disruption prediction analyses to support continuous operation of high beta KSTAR tokamak plasmas. The present work significantly expands prior magneticsonly equilibrium reconstruction capability. [1] The present kinetic equilibrium reconstructions include Thomson scattering data, charge exchange spectroscopy data, and allowance for fast particle pressure in addition to external magnetics and shaping field current data, and inclusion of vacuum vessel and passive plate currents following an approach used successfully in NSTX. [2] In addition, up to 25 channels of Motional Stark Effect data are used to constrain the local magnetic field pitch angle to produce reliable evaluation of the safety factor, q, profile. Approaches to minimize variation of the reconstructed pressure and magnetic pitch angle profiles within the data error are examined to reduce uncertainty in the subsequent stability analysis used for disruption event characterization and forecasting (DECAF). [1] Y.S. Park, S.A. Sabbagh, J.W. Berkery, et al., Nucl. Fusion 51 (2011) 053001. [2] S.A. Sabbagh, A.C. Sontag, J.M. Bialek, et al., Nucl. Fusion 46 (2006) 635.  

CP11.00100: Investigation of MHD Stability and Active Mode Control Supporting Disruption Avoidance on KSTAR YoungSeok Park, Steven A Sabbagh, John W Berkery, Jaeheon Ahn, Yanzheng Jiang, Juan Riquezes, ByungHo Park, Hyunsun Hahn, JunGyo Bak, YoungMu Jeon, Jayhyun Kim, SangHee Hahn, Minjun Choi, HyunSeok Kim, JongHa Lee, Jinseok Ko, SiWoo Yoon, Nathaniel M Ferraro, Zhirui Wang, Alan H Glasser Hmode plasma operation in KSTAR has surpassed the computed n = 1 ideal nowall stability limit for several seconds in duration. High normalized beta operation was limited by resistive tearing instabilities rather than RWMs. Kinetic equilibrium reconstructions including MSE data have been developed for accurate stability and transport analysis. The reconstructed high performance equilibria can exhibit significant variation of the qprofile dependent upon the broadness of the bootstrap current profile as computed by TRANSP code. The stability of the observed m/n = 2/1 tearing mode is computed by using the resistive DCON code and the M3DC^{1} code. MISK code analysis examining global MHD stability modified by kinetic effects shows significant passive kinetic stabilization of RWMs. To accurately measure the dynamics of unstable RWMs expected to onset at higher beta by utilizing the newly installed second NBI system, realtime mode identification and active control has been developed in the KSTAR PCS including magnetic sensor compensation of the prompt applied field and the field from the induced current in the passive conductors. This analysis provides the foundation for disruption prediction and avoidance research on KSTAR.  

CP11.00101: Calibration and performance evaluation of MSE WavelengthInterpolation Background Subtraction on KSTAR Steven Douglas Scott, Jinseok Ko, Robert Mumgaard, Juan Riquezes In 2018, fifteen additional sightlines of a background polychromator system were fabricated and installed on the KSTAR MSE diagnostic, which now can subtract partiallypolarized background light via wavelength interpolation on all 25 sightlines. This paper will discuss several calibrations of this instrument: standard polarizationangle calibrations with a rotating linearlypolarized light source; beamintogas calibrations to optimize filter passband placement relative to the beamgenerated MSE spectrum; and calibrations to quantify Faraday rotation in the optical system. The overall system performance including measurement accuracy and ability to accurately measure /compensate the partially polarized background light over a range of plasma conditions will be discussed, based on data acquired in the upcoming KSTAR 2018 experimental run campaign. Preliminary considerations for the use of the polychromator channels that measure background light to provide a measurement of the Zeff profile will be presented.  

CP11.00102: Interpretive and predictive transport analyses of KSTAR plasmas supporting disruption event characterization and forecasting Jaeheon Ahn, Steven A Sabbagh, YoungSeok Park, John W Berkery, Yanzheng Jiang, Juan D Riquezes, Mark D Boyer, Francesca M Poli, Steve D Scott, Jisung Kang, Hyungho Lee, Laurent Terzolo, Sonjong Wang, Alan H Glasser KSTAR plasmas have reached high stability parameters (normalized beta β_{N} reaching 4.3) at relatively low plasma internal inductance l_{i} (β_{N}/l_{i}>6), including operation at high β_{N} > β_{N}^{nowall} [1]. Transport analyses are conducted to best understand a disruptionfree path toward the design target of β_{N}=5 while aiming to maximize the noninductive current fraction f_{NI}. Interpretive analysis using the TRANSP code indicates that f_{NI} in existing KSTAR plasmas can reach up to 75%. It also shows that the bootstrap and total noninductive current profiles can vary significantly with f_{NI} across the regimes. The predictive capability of the TRANSP code is used to examine the effects of the second NBI system installed on KSTAR for the 2018 run determining plasma parameters and profiles important for plasma stability. Values of the global energy confinement quality (H98y2) and the Greenwald density fraction are set to match past KSTAR performance for reliable extrapolation. These ‘predictfirst’ analyses are used to design 2018 highβ experiments yielding solutions with β_{N}~4.5 at f_{NI}~100%. Ideal and resistive stability of MHD modes is evaluated using the DCON code. [1] Y.S. Park, S.A. Sabbagh, et al., Phys. Plasmas 24 (2017) 012512.  

CP11.00103: Progress of high β_{N} plasma operation on EAST tokamak Xiang Gao, Long Zeng, Haiqing Liu, Guoqiang Li, Gongshun Li, Huishan Cai, Xuemei Wu, Kazuaki Hanada, Yu Gao, Tingfeng Ming, Tao Zhang, Yao Yang, Zixi Liu, Muquan Wu, Kai Li, Xiang Zhu, Bo Lyu, Yinxian Jie, Qing Zang, Hang Li, Yunfeng Liang, Xianzu Gong, Jiangang Li Sustained high normalized beta (β_{N} ~ 1.9) plasmas with an ITERlike tungsten divertor have been achieved on EAST tokamak recently. The high power NBI heating system of 4.8 MW and the 4.6 GHz lower hybrid wave of 1 MW were developed and applied to produce edge and internal transport barriers in high β_{N} discharges. The central flat q profile with q(ρ) ~ 1 at ρ < 0.3 region and edge safety factor q_{95} = 4.7 is identified by the multichannel farinfrared laser polarimeter and the EFIT code. The fraction of noninductive current is about 40%. The relation between fishbone activity and ITB formation is observed and discussed.  

CP11.00104: NonInductive Vertical Position Measurement by FaradayEffect Polarimetry on EAST Tokamak D.L. Brower, W.X. Ding, Jie Chen, H.Q. Liu, J.P. Qian, Z.Y. Zou, Y.X. Jie, B.J. Xiao, Z.P. Luo, X.Z. Gong, L.Q. Hu, Baonian Wan The vertical position for elongated, longpulse tokamak plasmas has to be precisely controlled to optimize performance and prevent disruptions. For a steadystate tokamak reactor, integration of voltage signals arising from flux change is extremely challenging due to zerooffset drift as the measurement is intrinsically inductive. The vertical position of the plasma core current density is defined as the position where radial magnetic field is zero, making this parameter critical to investigating vertical instability. A Faradayeffect POlarimeterINTerferometer system has been developed for measuring the internal radial magnetic field in EAST. Horizontallyviewing chords at/near the midplane allow us to determine plasma vertical position noninductively with subcentimeter spatial resolution and 1 ms time response. The polarimeterbased position measurement, which does not require equilibrium reconstruction, is benchmarked against conventional flux loop measurements for EAST discharges. Noninductive vertical position measurements are very promising for future steadystate plasmas and fast time response allows for direct feedback on plasma vertical displacement instabilities.  

CP11.00105: Fast vertical control in superconducting tokamaks Dennis Mueller, Sanghee Hahn, Bingjia Xiao, David Humphreys For superconducting tokamaks like KSTAR, EAST and ITER the use of normal conducting coils internal to the vacuum vessel have been chosen as the actuator for fast vertical control. Modelling by the General Atomics control group and others have specified coil locations and power supplies for the internal vertical control (IVC) coils needed necessary for fast vertical control. Both EAST and KSTAR have used their IVC coils for vertical control since early in their operation. The control achieved early in their campaigns was limited by experimental realities. Conducting passsive plates used for stability control slow the response of the plasma to the IVC coils and the response of sensor coils to the plasma. Recent progress on identifying which sensors in KSTAR have both the sensitivity and fast response needed for feedback control is being extended to EAST. Both devices have implemented a separation of the time response to use the IVC coil for only fast deviations from the plasma vertical position determined by the plasma control system, primarily determined by the superconducting coils. The results of vertical control using the newly selected sensors for each machine will be discussed along with implications for ITER.  

CP11.00106: First experimental result of disruption mitigation by shattered pellet injection on JTEXT tokamak Zhongyong Chen The mitigation of disruption damage is essential for the safe operation of a largescale tokamak. Disruption mitigation by shattered pellet injection (SPI) has been proposed to achieve safe operation of ITER. A dedicated argon SPI system that focuses on disruption mitigation and runaway current dissipation has been designed for the JTEXT tokamak. The pellet can be injected with speed of 200300 m/s. The performance of disruption mitigation by Ar SPI has been compared with identical Ar massive gas injection (MGI). The cooling process observed from the ECE indicates that the SPI has deeper deposition. The current quench rate of SPI induced disruption is more than 100 MA/s. The increase of plasma density during fast shutdown is higher than that with identical Ar MGI. The dissipation of runaway current by Ar SPI is about 12 MA/s, which is lower than that with Ar MGI.  

CP11.00107: Beta induced Alfven Eigenmode Driven by Fast Ions in HL2A plasma Peiwan Shi, Wei Chen, Zhongbing Shi, Xuru Duan Researches on beta induced Alfven eigenmodes (BAEs) driven by fast ions have been carried out in HL2A plasma. The mode frequencies are around 3595kHz. The poloidal/toroidal mode numbers are m/n = 3/2 or m/n = 2/2 when the q_{min}_{ }is higher or lower than unit, respectively. They localize at the core region and their radial mode structures have been detected by the multichannel microwave reflectometer. The BAEs are confirmed by the theoretical calculations given by the general fishbonelike dispersion relation (GFLDR) and Alfven mode code (AMC). Both the mode frequency and location are found to agree with each other between experimental measurements and theoretical calculations. There is a density threshold for the excitation of BAEs. The modes are excited more easily in low electron density discharges and suffer stronger ion Landau damping in high density cases. The BAEs can coexist with reversed shear Alfven eigenmodes (RSAEs), which performs the MHD spectroscopy well. Finally, the amplitude and growth rate of the frequency chirping BAEs will provide inputs for simulations of potential ion and alpha particle losses due to energetic particle driven modes.  

CP11.00108: Implementation and Testing of Modelbased Optimal Control Strategies for qprofile Feedback Regulation in EAST Hexiang Wang, William Wehner, Eugenio Schuster, Yao Huang, Haiqing Liu, Zhengping Luo, Shouxin Wang, Qiping Yuan, Bingjia Xiao, Weixing Ding, David Humphreys Regulation of the qprofile via feedback control has been demonstrated experimentally in EAST for the first time ever. Extensive studies have shown that the qprofile, which is closely related to poloidal magnetic flux profile, is a key factor to achieving advanced tokamak operating scenarios that are characterized by improved confinement and possible steadystate operation. A general framework for realtime feedforward + feedback control of magnetic and kinetic plasma profiles has been implemented in the EAST Plasma Control System (PCS). Moreover, a firstprinciplesdriven, controloriented model of the poloidal magnetic flux profile evolution has been used to design a linear quadratic integral (LQI) controller for qprofile regulation in EAST. The proposed controller has been tested successfully in reference tracking and disturbance rejection experiments. These experiments constitute the first time ever a modelbased, closedloop, qprofile controller has been successfully implemented and tested in EAST.  

CP11.00109: Investigation of energy transport of high β_{N} plasma on EAST tokamak Muquan Wu, Guoqiang Li, Xiang Gao, Kai Li, Xiang Zhu, Qilong Ren, Long Zeng, Haiqing LIU, Shouxin Wang, Tao Zhang, Yao Yang, Bo Lyu, Qing Zang, Xianzu Gong In the past few years, the high normalized beta (β_{N} >1.8) discharges have been realized on the EAST tokamak with neutral beam injection(NBI) and lower hybrid waves(LHW). It is found that LHW most deposits in the outer region and drives small current fraction and does small effect on the increase of β_{N}. Sustained high β_{N} (~ 1.9) plasmas have been achieved on EAST tokamak with an internal transport barrier (ITB) in all channels. The central flat q profile with q(ρ) ~ 1 at ρ < 0.3 region and edge safety factor q_{95} = 4.7. Linear analysis shows that the highk modes instability (electron temperature gradient driven modes) is suppressed in the core region when the ITB is formed. Turbulence transport code TGLF[VX model, Jian et al., Nucl. Fusion 58, 016011(2018)] gives good agreements on temperature profiles prediction before the ITB formation. However, it could not reproduce the experimental temperature profiles when exist internal transport barriers. The reason is that the fishbone instability appears in the discharge, which could redistribute the fast ion and affect the energy transport while it is not considered in TGLF. The relationship between fishbone activity and the energy transport needs to be investigated for these high β_{N} discharges in order to validate this conjecture.  

CP11.00110: Rotating MHD analysis for disruption event characterization and forecasting Juan Diego Riquezes, Steven Anthony Sabbagh, John W Berkery, YoungSeok Park, Yanzheng Jiang, Jaeheon Ahn, Ronald E Bell, Eric Donald Fredrickson, Lucas A Morton Steady plasma operation in reactorscale tokamaks such as ITER can be maintained through disruption forecasting and avoidance tools. Automated identification of events relevant to disruptions is a required step in developing such tools. Significant physical events are the presence of rotating MHD modes inside the plasma. An analysis of their rotational frequency behavior can be used to identify the event chain where they are slowed by resonant field drag mechanisms and lock in the lab reference frame leading in many cases to a disruption. An algorithm has been developed that automatically detects bifurcation of the mode toroidal rotation frequency due to loss of torque balance under resonant braking and mode locking using spectral decomposition. Criteria are examined to determine the severity of the mode state in progressing toward a potential disruption. Low and medium frequency magnetic probes, plasma rotation profiles from charge exchange recombination spectroscopy, and equilibrium quantities including normalized beta and internal inductance are utilized to provide warning levels to a disruption. A variety of mode conditions are examined using these criteria for NSTX/U and KSTAR plasmas.  

CP11.00111: Progress of Concept Design for CFETR diagnostic system Gongshun Li, Xiang Gao, Yao Yang, Qingsheng Hu, Xiaodong Lin, Guoqiang Li, Yumin Wang, Tingfeng Ming, Shaocheng Liu, Erhui Wang, Xiang Han Chinese Fusion Engineering Test Reactor (CFETR), as the next superconducting tokamak device in the roadmap for the realization of fusion energy in China, aims at bridging the gaps between ITER and DEMO, and has started an integration engineering R&D project since December 2017. This paper will presents current progress of CFETR diagnostic design, which mainly includes three sections: 1) constraints in CFETR environment for diagnostic system, such as high level of neutron flux and influence; 2) one set of candidate measurements and corresponding techniques, which was proposed for CFETR phase I based on ITER’s experience; 3) current status on diagnostic port plug design, such as electromagnetic performance, nuclear shielding, thermal load, remote handling maintenance, etc.  

CP11.00112: Optimization of Plasma Shape of the CFETR by Static Equilibrium Calculation Hang Li, Guoqiang Li, Xiaoju Liu, Rui Ding, Jinping Qian, Jinxing Zheng The zerodimension parameter of the CFETR has been updated in 2018. The calculation of equilibria must give the operating space of the plasma configurations in extreme status, so as to provide a reference to other design issues, such as the physical study of the divertor and optimum design of the poloidal field (PF) coils. By using the TEQ, a sequence of standard Hmode equilibria with a wide range of internal selfinductance (li) and triangularity were established. The iteration of the equilibrium and divertor structure progressed until the result met the requirements in physics and engineering. A comparison of PFcoil designs from different coil positions was performed to demonstrate that it is indeed possible to sustain significant flux for the current flattop phase while PF coil currents are all under their limits. With additional PF coils inside the vacuum vessel, currents in some PF coils decreased, we then show that it is possible to build advanced diverted plasma configurations which would be beneficial for reducing highpower load on divertor targets.  

CP11.00113: Influence of magnetic island on edge plasma flows and turbulence properties in JTEXT Jie Yang, Peng Shi, Zhipeng Chen Magnetic islands in magnetically confined plasmas are found to have significant effects on the profiles and crossfield transport [1]. And the multiscale physics such as the interaction between largescale MHD modes and turbulence are reported to play a crucial role in the transport regulation [2]. In the recent campaign on JTEXT tokamak, a new experiment has been carried out which aimed to study the plasma flows and turbulences nearby static magnetic islands, using the Langmuir probe and laser collective scattering system. The edge 3/1 island has been excited by applying the resonant magnetic perturbation (RMP) with dominate m/n=3/1 component to a plasma with edge safety factor q_{a}>~3. This research mainly focuses on three aspects: the effects of variant island size, island location and island phase. Once the condition of 3/1 island has been changed, the radial profiles of plasma density (n_{e}), temperature (T_{e}), floating potential (V_{f}) etc measured by Langmuir probe varied significantly, and the plasma flow and turbulence are also modulated obviously. [1] Inagaki S. et al 2004 Phys. Rev. Lett. 92 055002 [2] Choi M.J. et al 2017 Nucl. Fusion 57 126058  

CP11.00114: Study of argon impurity transport by Xray imaging crystal spectrometer on JTEXT Wei Yan, Zhongyong chen, Xiaolong Zhang, Zhifeng Cheng, Rui hai Tong, Yunong Wei, Zhifang Lin A tangential Xray imaging crystal spectrometer (XICS) has been designed to receive emissions of Ar XVII from −13 cm to +13 cm region with a spatial resolution of 1.8 cm in the vertical direction on JTEXT. The temporal evolution of argon impurity density profiles after an argon gas puff could be observed with a time resolution of up to 2 ms. The emissions of Ar XVII can be modulated by the resonant magnetic perturbations (RMPs) which indicates that the transport of argon is affected by the RMPs significantly. The 2/1 RMPs can lead to field penetration with enough RMPs amplitude. The XICS provides a tool for the study of the transport of argon impurities during the penetration of RMPs. During the field penetration phase, the emissions of Ar XVII decreased. The phenomena show that the transport of argon impurity in the core region has been enhanced during the field penetration phase. STRAHL can give the ratio between D and v profiles for the argon. The result shows that the argon is moving towards the core by the convection.  

CP11.00115: Effect of resonant magnetic perturbations on plasma rotation on JTEXT tokamak Xiaoyi Zhang The plasma rotation in edge region has been studied with the locked 2/1 and 3/1 magnetic island excited by the magnetic resonant perturbations respectively on JTEXT tokamak. In the case of 2/1 magnetic island, it is observed that the toroidal rotation of carbon V changes significantly during the mode locking, shifting from the countercurrent to cocurrent direction. The variation of the rotation of carbon V is found to depend on the RMP current and phase. In the case of 3/1 magnetic island, the locked mode has a relatively small impact on the rotation of carbon V, but a significant impact on the rotation of carbon III, which locates in the outer region. The shift of toroidal rotation of carbon III is normally in cocurrent direction. However, in specific phase, the countercurrent direction shift of toroidal rotation of carbon III is also observed. It is suggested that the effect on the localized rotation might be contrary in and out of the magnetic island. The combined impacts of the magnetic islands and the understanding of the roles on plasma rotation will be presented and discussed in the conference.  

CP11.00116: Critical gradient scale length measurements via variable location ECE channels in the EAST tokamak Saeid Houshmandyar, Max E. Austin, He Huang, Yong Liu, William L. Rowan, Hailin Zhao ECE radiometers that implement variable location channels using yttrium iron garnet (YIG) bandpass filters are capable of realtime ∇T_{e }and a/L_{Te} (where ais the minor radius and L_{Te}= T_{e}/∇T_{e}) measurements with submillisecond temporal resolution [Houshmandyar et al., Rev. Sci Instrum., 2018]. The key features of the YIG filters in these measurements are their narrow bandwidth and fast frequency switching at any given center frequency. These permit rapid relocation of the ECE channels, direct and calibrationfree measurement of a/L_{Te}, and close spacing of the ECE channels, which can be done in real time during a plasma discharge. At the EAST tokamak, two YIG filters were substituted for the fixed filters in the IF section to permit gradient scale length measurements by fast slewing of their center frequencies. Electrons were heated via ECRH at different power levels and power deposition locations for the intent of varying the electron heat flux and simultaneously, gradually change the local gradient. The power balance analysis (Q/Q_{GB}) and the measured scale length (a/L_{Te}) resulting in the critical gradient scale length measurements at the two major radii, as well as turbulence measurements via CECE will be presented.  

CP11.00117: First measurements of edge impurity flow across the LH transition in TCV Claudio Marini, Basil Duval, Alexander Karpushov, Yann Camenen Recent upgrades of the CXRS diagnostic, together with a low power diagnostic neutral beam injector, have, for the first time, enabled accurate measurement of the changes in the impurity intrinsic flow across the transition to ELMfree Hmode on TCV. Photon statistics limited the time resolution to 12 ms, for a 30 Hz measurement frequency.  

CP11.00118: Measurements and theoretical comparisons of electron turbulence at ASDEX Upgrade Simon James Freethy, Anne Elisabeth White, Alexander J Creely, Garrard D Conway, Severin Denk, Emiliano Fable, Tobias Goerler, Tim Happel, Pascale Hennequin, Pablo Rodriguez Fernandez At ASDEX Upgrade, a Correlation ECE diagnostic with a novel channel comb is used to probe the fundamentals of ionscale electron heat transport. It measures radial profiles of lowk (k_{θ} < 0.3) temperature fluctuations_{,} and radial correlation lengths, L_{r}(T_{e}), in unprecedented detail. This diagnostic is augmented by the addition of a reflectometer on the same line of sight to enable measurements of the crossphase angle between turbulent n_{e} and T_{e} fluctuations, α_{nT}. These measurements are used as quantitative constraints on nonlinear ionscale gyrokinetic simulations, with good overall agreement. α_{nT} is a good indicator of the balance of Trapped Electron and Ion Temperature Gradient modes and therefore the measurement puts a strong constraint on the simulation in combination with Q_{i}/Q_{e}. A validation metric is used to plot trends of agreement between the simulation set and experiment, and a minimum is found close to the experimental inputs. Fluctuating quantities and trends are also compared to TGLF predictions across the ITG/TEM transition.  

CP11.00119: Key effects on the core confinement improvement of AUG hybrid scenario Xiang Jian, Vincent Chan, Jiale Chen, Alexander Bock, Hartmut Zohm, Ge Zhuang Hybrid mode is a prime candidate for longpulse/steadystate operation in future fusion reactors. Transport analysis of a fully noninductive high performance ASDEX Upgrade(AUG) hybrid shot(A.Bock, Nuclear Fusion, 2017) is performed. It is shown that the confluence of several mechanisms is essential for the improvement in core confinement. In addition to the rotation shear, low magnetic shear, which is a common characteristic near the magnetic axis of hybrid scenario, is found to be favorable for both electromagnetic and alpha stabilization. Together they prepare the stage such that the presence of fast ions facilitates the transition to a strong local ITB due to additional dilution effect and enhancement of alpha stabilization. This study presents for the first time that a quasilinear turbulent model is capable of quantitatively matching the experiment temperature profile across the entire core. Such a model can thus be used with confidence to design hybrid operating scenarios for ITER and CFETR.  

CP11.00120: Modeling of AUG pellet discharges Giovanni Tardini, Clemente Angioni, Emiliano Fable, Peter Lang Particle transport in tokamaks has been widely investigated both experimentally and  

CP11.00121: First result of edge impurity transport with EMC3EIRENE code in HL2A plasmas Chunfeng Dong, Yuhe Feng, Masahiro Kobayashi, Xuejun Zha, Zhengying Cui, Jianqiang Xu, Jun Cheng, Zengchen Yang, Rui Ke, Ping Sun, Kai Zhang, Dianlin Zheng, Lei Feng, Xianli Huang, Zhongbing Shi, Qingwei Yang, Min Xu Understanding of edge impurity transport is essentially important for impurity control and detached divertor operation, which are the key points to realize highperformance plasma. The EMC3EIRENE simulation code is focused on the edge plasma transport and successfully applied to many machines to resolve the transport with 3dimentional magnetic structure. The RMP coils have been installed in HL2A, therefore it is necessary to apply the EMC3EIRENE code to HL2A plasmas. The computational grid is firstly generated for each magnetic configuration of interest as the input of EMC3EIRENE. The edge temperature and density profiles measured by probe system are used for adjusting the transport coefficients of background plasmas. Good agreement in ohmic phase is obtained with D_{⊥}= 0.3m^{2}s^{−1} and χ_{⊥} = 1.5m^{2}s^{−1}. The profile of CIV line emission (312.4Å: 1s^{2}2s  1s^{2}3p) obtained from simulation is compared with experimental result measured by the spaceresolved extreme ultraviolet spectrometer. Analysis shows that the thermal force is dominated in ECRH heating plasma instead of the dominant friction force in ohmic heating plasma, resulting the enhancement of CIV intensity in ECRH heating phase. The detailed analysis on carbon impurity transport based on EMC3EIRENE code will be presented.  

CP11.00122: Plasma radiation losses and particle transport on the GlobusM tokamak Alsu Sladkomedova, Andrey Alekseev, Vasily Gusev, Gleb Kurskiev, Vladimir Minaev, Yury Petrov, Nikolay Sakharov, Sergey Tolstyakov, Alexandr Voronin, Vladimir Zabrodsky In this work the results of investigation of plasma radiation losses by means of a tomography diagnostic system are presented. The system is based on a 16×16 tangential matrix array and a 24×1 linear array of silicon photodiodes. Presented are the dependence of plasma radiation losses on plasma current, toroidal magnetic field and heating regime for a range of electron densities. Transport properties of the main plasma impurity, carbon, were analyzed using ASTRA and STRAHL codes by matching modelled and experimental plasma emissivity profiles and loop voltages. The 16×16 matrix array was used to explore the penetration of hydrogen and helium jets in the tokamak plasmas. Injection of the hydrogen jet led to the twofold increase in the core electron density. In the experiments, it was observed that the velocities of the jets decreased exponentially with the characteristic times corresponding to the deceleration mechanism due to the Alfvén conductivity.  

CP11.00123: Effect of parallel convection on divertor plasma turbulence driven by the currentconvective instability in DIIIDlike detached conditions Alexander Stepanenko, Huiqian Wang, Sergei Krasheninnikov
It has been recently suggested [Krasheninnikov and Smolyakov, PoP, 2016] that the currentconvective instability (CCI) can be responsible for formation of strong radiation fluctuations observed during the fluctuating state of detachment in experiments at ASDEX Upgrade (AUG) [Potzel et al., Nuclear Fusion, 2014]. The first numerical simulations of CCI dynamics, employing the basic physical model of the instability, have shown that this mechanism can indeed be a plausible candidate for the onset of turbulence with temporal parameters similar to those observed at AUG [Stepanenko and Krasheninnikov, PoP, 2018]. In this contribution we demonstrate the results of modeling the currentconvective turbulence in detached plasma within the extended physical model of the CCI, incorporating the effect of parallel plasma convection in the diffusion approximation. We show the frequency spectra of saturated turbulence in the DIIIDlike detached conditions and compare them with the available experimental data and simulation data obtained within the basic physical model of the instability.  

CP11.00124: Turbulent Plasma transport in the PKU Plasma Test (PPT) device Tianchao Xu, Chijie Xiao, Xiaoyi Yang, Zhibin B. Guo, Renchuan He, YiHang Chen, Dong Guo, Lin Nie, Rui Ke, Min Xu, Yi Yu, Long Wang, Xiaogang Wang Turbulent plasma transport causes the loss of particle and energy in magnetized plasma, which decrease the confinement of Tokamak plasma. Recently, a series of experiments have been carried out in the PPT device, to study turbulence transport including particle and energy transport. Combining both the highspeed camera and probe analysis, some problems of turbulence transport have been studied preliminarily. A lot of modes, such as drift wave turbulences, high frequency eigen modes, low frequency coherent structures, etc., are all observed. The interchange of energy and momentum between these modes are also identified. The interaction of multimodes may play an important role on the radial plasma transport of particle and momentum.  

CP11.00125: Development of a Use Case Database for Validation and Predictive Modeling in the AToM SciDAC Project Christopher G Holland The AToM (Advanced Tokamak Modeling) integrated modeling SciDAC project [1] is developing a “use case” database to facilitate benchmarking, verification and validation studies of physics model components and workflows, with an initial focus on core turbulent transport. The first group of use cases included in this database corresponds to welldiagnosed tokamak discharges spanning a range of plasma parameters and confinement modes. A second group of use cases corresponding to a variety of possible future burning plasma experiments is also included in the database. Put together, the database allows assessment of current model fidelity for existing experiments, and systematic comparisons of model predictions for future plasmas of interest. A variety of initial applications will be shown, including comparisons of core profile predictions made using the TGLF “SAT0” [2] and “SAT1” [3] models. Future plans including gyrokinetic studies, validation metric development, and extensions to the database to support physics studies beyond core transport will be discussed.
[1] https://scidac.github.io/atom/ [2] G. M. Staebler et al., Phys. Plasmas 23 0625108 (2016) [3] G. M. Staebler et al., Phys. Plasmas 14 055909 (2007)  

CP11.00126: Understanding, Triggering and Controlling Imode like enhanced confinement regimes using Cross Phase mechanisms David Newman, P. W. Terry, Raul Sanchez, Soma R Panta The enhanced confinement offered by Imodes and similar new transport regimes offer improved confinement properties with reduced density limit issues and potentially better control. We have proposed differential crossphase modification as a possible mechanism for different transport in different channels. This is investigated theoretically with a reduced fluidkinetic hybrid model which illustrates a mechanism for varied cross phase different regimes. Nonadiabatic particle responses incorporate thermodiffusive pinch physics for electrons in ITG and FLR effects for ions in ETG. Moving from ITG dominated regime to an ETG dominated regime the pinch can be dominant or subdominant controlling the particle transport and pump out. Computationally, this is investigated with a dynamical transport model. By including in this transport model a model for cross phase effects, due to multiple instabilities, between the transported fields such as density and temperature, we can investigate whether the dynamics of more these continuous transitions such as the Imode can be captured and understood. If correct this could have broad implications for transport in many systems. Finally, we investigate the control knobs for triggering and controlling these promising regimes.  

CP11.00127: Advanced tokamak scenarios, ITB dynamics and instabilities in fusion plasmas Soma R Panta, David E Newman, Paul W Terry, Raul Sanchez For a selfsustained fusion power plant, selfgenerated noninductive current drive has to be maintained by bootstrap current that is mostly due to very high plasma pressure. Plasma with central reverse magnetic shear has peaked current density near the shear reversal position. Such a configuration has a steep pressure profile that can lead to E X B shear flows that can reduce or suppress the turbulence driven by the free energy coming from the gradient in the profiles. These internal transport barriers(ITBs) help improve confinement but need to be controlled to prevent instabilities and clean the ash. To both maintain the steep profiles and to relax them, auxiliary heating like neutral beams and radio frequency heating as well as pellet can be used as control tools. Position, amplitude and deposition width have important roles. Optimizing these parameters ITBs can be controlled in fusion devices. Demonstration scenarios in current and future devices will be investigated.  

CP11.00128: Evidence for Particle Inward Transport, Theoretical Prediction and Importance for Reacting Plasmas Cristina Mazzotta, Bruno Coppi The fact that particle transport cannot be described by a diffusion equation but by one [1,2] that would include an inflow term, involving transport in the direction of the density gradient, was evidenced by experiments on magnetically confined plasmas in which the central plasma density was observed to increase as a result of gas injection at the edge of the plasma column. The validity of the proposed equation has been repeatedly confirmed over the years and limitations for the occurrence of particle inflow in a variety of experimental conditions have been uncovered. The direct experimental observation of the inward propagating particle cloud leading to a profile peaking [3] is described and the effects of different degrees of density peaking in fusion burning plasmas are analyzed.
 

CP11.00129: Quasilinear fluxes for parallel magnetic fluctuations Gary Staebler The Trapped GyroLandau Fluid (TGLF) equations [1] do not have enough velocity space moments to compute the energy and momentum transport contributions from parallel magnetic field perturbations. A higher moment system requires determining new closure coefficients. The curvature drift resonance closure coefficients in TGLF are computed using the BeerHammett method [2]. This method numerically determines the closure coefficients that minimize the error in a fit to linear response functions. Unfortunately, the fitting procedure does not result in gyroLandau fluid quasilinear fluxes that preserve the Onsager symmetries. A new system of linear gyrofluid equations is derived with closure coefficients that preserve Onsager symmetries. A system of equations with enough velocity space moments to compute the full set of electromagnetic fluxes is constructed. The importance of the parallel magnetic fluctuations for transport is assessed for high beta spherical tokamak discharges in MASTU. [1] G. M. Staebler, J. E. Kinsey, and R. E. Waltz, Phys. Plasmas 12 (2005) 102508. [2] M. A. Beer and G. W. Hammett, Phys. Plasmas 3 (1996) 4046.  

CP11.00130: Temperature Screening of Impurities in Stellarators and Tokamaks Deviating From Symmetry Mike F Martin, Matt Landreman, William D Dorland Quasisymmetric stellarator configurations aim to combine the stability of stellarators with the confinement of tokamaks, making them particularly interesting for optimization efforts. However, perfect quasisymmetry can only be achieved on a single flux surface at best, making it useful to study configurations with small deviations from perfect quasisymmetry, a regime in which devices will unavoidably have to operate. A particular phenomenon that occurs in tokamaks, which are naturally quasisymmetric, is a favorable outward radial flux of highly charged impurity ions, commonly referred to as impurity temperature screening. Conversely, stellarators generally display an inward impurity flux, causing an impurity accumulation in the core that can be detrimental to performance. Given realistic levels of departure from symmetry in stellarators or tokamaks, will real experiments have an outward impurity flux consistent with tokamaks, or an inward flux like nonsymmetric stellarators? We use the SFINCS driftkinetic solver to calculate neoclassical fluxes in order to investigate this property over various parameter regimes and configurations.  

CP11.00131: A LargeAspectRatio Multiscale Pedestal Ian Abel Understanding of the behaviour of tokamak pedestals is critical to forging a path towards efficient fusion reactors. Existing models [1] of the pedestal region are focused on modelling experiment. These models have achieved great success but some of the underlying physics remains obscure.  

CP11.00132: Edge momentum transport within an extended MHD code Jacob King, Scott E Kruger, Alexei Pankin, Eric C Howell, Brian A Grierson, Richard Joseph Groebner, Eric D Held, Andy Spencer, Sina Taheri, Uri Shumlak Edge plasma flows with large shear are correlated with the occurrence of Quiescent Hmode (QHmode) [1] as opposed to operation with edge localized modes (ELMs). Prior NIMROD MHD simulations of QHmode [2] use implicit sources that maintain the flow profiles. However, these implicit sources complicate the MHDinduced transport analysis and a higherfidelity model is needed. This work studies the forces and nonlinear flow evolution within the context of extended MHD. Our simulations are initialized with a reconstructed DIIID state where the flow is measured by both mainion and Carbon impurity chargeexchange recombination spectroscopy. We then study the evolution with MHD with Braginskiilike closures coupled to a fluidneutral model. Progress towards including a driftkinetic closure [3] for the force density from the neoclassical stress and ionorbit loss is discussed. [1] KH Burrell et al., Phys. Plasmas 12, 056121 (2005)  

CP11.00133: Simulation study of toroidal flow generation by ECH in nonaxisymmetric toroidal plasmas Sadayoshi Murakami, Yasuhiro Yamamoto, ChingChieh Chang, Hiroyuki Yamaguchi, Hiromi Takahashi, Kenichi Nagaoka, Katsumi Ida, LHD EXP Group Spontaneous flows have been observed during ECH with no direct momentum input in tokamak and helical plasmas. In LHD, when we applied ECH to the NBI heated plasma, the toroidal velocity profile changed drastically. We assume that the radial flux of suprathermal electron enhances the bulk ion cancelling current. This current generates the JxB torque, which would play an essential role in causing a toroidal flow.  

CP11.00134: NIMROD Modeling of Poloidal Flow Damping in a Tokamak Using a Drift Kinetic Equation Closure Scheme Joseph Jepson, Chris C Hegna, Eric Held Calculations of poloidal flow damping in a tokamak are undertaken using two implementations of the ion drift kinetic equation (DKE) in the extended MHD code NIMROD. The first implementation utilizes a conventional deltaF approach, while the other employs a ChapmanEnskoglike (CEL) ansatz. The CEL ansatz specifies that the n, V, and T moments of the kinetic distortion are identically zero. The closure information needed for the loworder fluid evolution equations are provided by solutions to the ion CELDKE written in the macroscopic flow reference frame [1]. Initial value calculations are performed for an axisymmetricshaped tokamak with an imposed kinetic distortion that initially provides a mean poloidal flow fluid velocity. The computational results are compared with analytic predictions of timedependent closures for the parallel viscous force and for the poloidal flow damping [2]. The computational results are also compared and contrasted between the two implementations, to verify the consistency, efficiency, and accuracy of each approach. [1] J. J. Ramos, Phys. Plasmas 18, 102506 (2011). [2] A. L. GarciaPerciante et al, Phys. Plasmas 12, 052516 (2005).  

CP11.00135: Role of Toroidal Rotation in ITB Formation in Tokamaks Tariq Rafiq, Eugenio Schuster, Alexei Pankin, Johan Anderson A set of tokamak discharges with internal transport barriers (ITBs) are studied using the TRANSP code in order to investigate the role of toroidal rotation in triggering of ITBs. The toroidal momentum transport is predicted using theorybased MultiMode and TGLF anomalous transport models to compute the toroidal rotation profiles and the effects of turbulence quenching as a result of associated sheared flows. The effect of co versus counter injected beams on the location and strength of ITBs is studied. Results are presented for existing discharges in order to illustrate the extent to which the MultiMode and TGLF models in TRANSP code yield toroidal rotation profiles that are consistent with experimental data. The comparison is quantified by calculating the RMS deviations and Offsets. The selfconsistent evolution of the equilibrium is computed using the TEQ module. Neoclassical transport is calculated using the ChangHinton model. NBI and ICRF heating and current drive are obtained using the NUBEAM and TORIC modules.  

CP11.00136: Simulating magnetic fusion experiments with initial value codes Scott E Kruger, Jacob R King, Alexei Pankin, Eric C Howell Fusion laboratory experiments are characterized by large gradients as is needed to confine plasmas hotter than the sun in laboratory devices. These large gradients result in a widerange of instabilities. In toroidallyconfined plasmas these linear instabilities (e.g., $1/1$, TM, ITG) evolve nonlinearly to produce phenomenological events (e.g., sawtooth, MARFE, transport). The phenomenological events are generally of three types: violent relaxation (or transients), coherent saturated steady state, and turbulent steady state. How to formulate the simulation of experiments with an initial value code requires understanding the phenomenological type, and appreciating the subtle implications of the solution technique. These subtle implications are discussed generally, and then specifically in the context of simulating QHmode, ELMfree regimes.  

CP11.00137: Datadriven approach to plasma profile evolution for plasma control Joseph A Abbate, Egemen Kolemen Highcurrent disruptions must be avoided in ITER to prevent prohibitively expensive damage. Most modern Plasma Control Systems partially solve this problem by predicting disruptions in real time and shutting down the experiment altogether when necessary. However, a more useful system would automatically vary controllable parameters (such as ECH and neutral beam systems) to guide the shot along a path that circumvents instabilities before disruptions are imminent. This study tackles the first step toward such a system: predicting the future evolution of a shot based on the history of the shot up to the current moment. Using first principles simulations for this task is notoriously slow and unreliable, so our approach is instead datadriven. A statistical / machine learning algorithm takes in the history of the pressure profile, current profile, plasma rotation, and a few other parameters at a time t. It then outputs the prediction for the profile at time t+1. By repeating this process iteratively on predicted steps with various options for the controllable parameters at each step, a Plasma Control System could set the controllable parameters to maintain safety with optimized performance.  

CP11.00138: From Lawson to Burning Plasmas: a MultiFluid Approach Luca Guazzotto, Riccardo Betti The Lawson criterion gives the value for the triple product of density, temperature and energy confinement time needed for the plasma to ignite. Lawson's work was improved, adding 1D geometry and multifluid (ions, electrons and alphas) physics to the model. Physical equilibration times and different energy confinement times between species were accounted for in steadystate (Lawsonlike) and timedependent calculations. At this time it is more meaningful to consider a finite gain factor Q. The plasma conditions needed to achieve any desired value of Q both in the 0D and the 1D multifluid plasma description can be evaluated through freelyavailable versatile Mathematica notebooks. Arbitrary density and temperature profiles can be assigned from input. Results are related with experimental puredeuterium discharges defining a noalpha pressure. Given the multifluid Lawson product needed for a desired Q the alpha heating is subtracted from the energy balance and the noalpha equilibrium pressure is obtained. The model easily allows to introduce scalings for energy confinement times. Including the τ_{E} dependence on power only one thermal equilibrium point exists for a given heating power instead of the two predicted by Lawsonlike calculations.  

CP11.00139: Resistive MHD Evolution of Shaped RFP Equilibria Joseph Newman, Andrew Ware, NIMROD Team Computational modeling of the resistive MHD evolution of reversefieldpinch (RFP) plasmas with boundary shaping is undertaken. The VMEC code obtains equilibria that are similar to quasisingle helicity (QSH) states in an RFP with a helical axis and a symmetric boundary [J.D. Hanson, et al., Nuclear Fusion 53, 083016 (2013)]. Previous work has shown that axisymmetric boundary shaping affects whether an axisymmetric or QSH equilibrium is obtained in VMEC. In this work these equilibria are used as initial conditions for the NIMROD code [C.R. Sovinec, et al., Phys. Plasmas 10, 1727 (20030]. Particular attention will be paid to the evolution of global tearing modes in both axisymmetric and helical equilibria.  

CP11.00140: Computational modeling of quasisingle helicity states in an RFP Andrew Ware, Carmen Miele, Joseph Newman Experiments have shown that RFP plasmas can selforganize to a quasisingle helicity (QSH) equilibrium with a helical axis [D.F. Escande, et al., Phys. Rev. Lett. 85, 1662 (2000)]. These states have improved confinement and lower magnetic turbulence levels compared to a standard RFP plasma. These experiments all have circular, or nearlycircular crosssections. This work explores the impact of boundary shaping on access to quasisingle helicity states in reversefieldpinch (RFP) plasmas. The VMEC code can obtain computational ideal MHD equilibria with a helical axis and a symmetric boundary [J.D. Hanson, et al., Nucl. Fusion 53, 083016 (2013)]. In this work, we analyze the VMEC input parameters that control access to QSH states and test the impact of 2Dshaping of the boundary on RFP equilibria. The effect of increasing elongation and triangularity are tested systematically. Increased elongation results in lower plasma current for the same safety factor profile and a larger radial excursion of the helical axis in a QHS state. Optimization of the boundary coefficients targeting an increased radial excursion of the helical axis is undertaken. Results will be presented.  

CP11.00141: Operation of the Lockheed Martin T4B experiment Michael Garrett, Frans H Ebersohn, Jonathon Heinrich, Christopher Lohff, Thomas J McGuire, Nicolo Montecalvo, Patrick W Ross, Aaron Schinder, Bradley S Sommers, Elizabeth K Strandberg, Regina Sullivan, Jonathan Walker The T4B experiment is a linear, encapsulated ring cusp confinement device. The mission of the T4B experiment is to develop a physics and technology basis for a followon high beta (beta ~1) machine, T5. The T4B experiment consists of 13 magnetic field coils (11 external, 2 internal), to produce a series of onaxis field nulls surrounded by modest magnetic fields of up to 0.3 T. A series of physics investigations were performed to retire risk from the T5 heating experiment, presently under construction. Following an initial test campaign used for machine checkout and diagnostic validation, a thorough investigation of plasma sources was completed. In addition, a series of Neutral Beam Injection (NBI) coupling tests were conducted to investigate fastion confinement and plasma source / NBI interaction. Finally, magnetic shielding experiments were performed to study the effect of local magnetic perturbations on particle losses to the internal coil support structures. Detailed results from these studies will be presented.  

CP11.00142: Simulation Support of the T4B Experiment Gabriel Font, Artan Qerushi, Thomas J McGuire The Lockheed Martin Compact Fusion Reactor concept utilizes magnetic cusps to confine plasma. Simulations are carried out in support of the T4B experiment. GradShafranov simulations are used to explore equilibrium stability. PIC simulations are conducted to understand the evolution of particle distribution functions, neutral beam heating efficiency and plasma confinement. ZeroDimensional models are used predict plasma evolution. Finally, collision radiative models are used to determine plasma density and temperature. © 2018 Lockheed Martin Corporation. All Rights Reserved.  

CP11.00143: Permanent Magnet Support Shielding for T4B Jonathon Heinrich, Frans H Ebersohn, Gabriel Font, Michael L Garrett, Jason Guyton, Artan Qerushi, Thomas J McGuire The linear encapsulated ring cusp topology of Lockheed Martin’s Compact Fusion Reactor (CFR) concept requires electromagnetic field coils internal to the plasma. These coils have supports that pass through the confined plasma volume. To reduce plasma losses and protect the coil supports, we are pursuing magnetic guarding. While magnetic guarding can invariably reduce plasma losses directly to supports, magnetic guard fields introduce crossfield plasma drifts (predominately grad B drifts). Depending on the ratio of the guard field to background magnetic field, these drifts can be negligible or become dominant loss mechanisms. As part of the T4B experimental campaign, various forms of magnetic guarding have been investigated. We present the experimental results for a simple prototype magnetically guarded support and demonstrate total plasma loss reduction due to the supports of greater than 55% in comparison with unshielded supports. © 2018 Lockheed Martin Corporation. All Rights Reserved.  

CP11.00144: Lockheed Martin Compact Fusion Project: Diagnostic Development and Comparison with Simulations Patrick Ross, Michael L Garrett, Christopher Lohff, Aaron Schinder, Bradley S Sommers, Elizabeth K Strandberg, Artan Qerushi The T4B experiment is a linear, encapsulated ring cusp confinement device, designed to develop a physics and technology basis for a followon high beta machine as part of the compact fusion reactor program. We present a suite of noninvasive diagnostics for the T4B experiment looking at several aspects of the plasma performance including plasma emissions (bolometry, spectroscopy), stability, and magnetic field perturbations. We also show comparisons of synthetic diagnostics to measured data. The synthetic diagnostics can be run with a variety of equilibrium reconstructions and simulations, and the results are compared against measured data to validate the models and correlate the data from the different diagnostics. Future diagnostic plans are also presented. © 2018 Lockheed Martin Corporation. All Rights Reserved.  

CP11.00145: Neutral Beam Development for the Lockheed Martin Compact Fusion Reactor Frans Ebersohn, Regina Sullivan The Compact Fusion Reactor project at Lockheed Martin Skunk Works is developing a neutral beam injection system for plasma heating. The neutral beam plasma source consists of a high current lanthanum hexaboride (LaB6) hollow cathode which drives a ring cusp discharge similar to gridded ion thrusters. The beam is extracted with a set of focusing grids and is then neutralized in a chamber pumped with Titanium gettering. The design, testing, and analyses of individual components are presented along with the most current full system results. The goal of this project is to advance inhouse neutral beam expertise at Lockheed Martin to aid in operation, procurement, and development of neutral beam technology.  

CP11.00146: Plasma Source Development for Lockheed Martin’s Compact Fusion Reactor Program Jonathan Walker, Zachary Harason, Adam M Steiner, Randall Sovereign, Nicolo Montecalvo, Jason Guyton, Thomas J McGuire, Jonathon Heinrich A multipronged plasma source development effort is underway for the Lockheed Martin Compact Fusion Reactor (CFR) program. The objective of the plasma source development effort is to build a plasma source that can provide a sufficiently dense plasma target for neutral beam heating in the CFR geometry (a linear encapsulated ring cusp). An ideal source would allow for high mirror ratios in the expansion regions (divertors) of the device, have a very high ionization fraction, have very low impurity levels, and create sufficiently dense plasma (>5 x 1019 m3). In addition to the arcreflex thermionic source currently employed on the T4B linear encapsulated ring cusp experiment, we are developing three alternative technologies: a high power (>2 MW) MagnetoPlasmaDynamic source (MPD), a crossfield (ExB) homopolar type source, and a high power (>400 kW), high field (>4 kG) RF source. We present the performance of these high power plasma sources.  

CP11.00147: An Overview of Laser Diagnostics Developed for the Compact Fusion Reactor Bradley S Sommers, Zachary Haralson, Aaron Schinder The T4B experiment is a linear, encapsulated ring cusp confinement device, designed to develop a physics and technology basis for a followon high beta machine as part of the compact fusion reactor program. Toward this end, a pair of noninvasive laser diagnostics have been developed to investigate confinement, neutral beam heating, and source behavior on the T4B device. These diagnostics include: (1) a Thomson scattering system employing a 532 nm Nd:YAG laser and high throughput spectrometer to measure electron density and temperature and (2) a dispersion interferometer utilizing a continuouswave CO2 laser (𝝀 = 10.6 μm) to measure time resolved, lineintegrated electron density. An overview of laser systems, detection schemes, and data analysis techniques for both systems is presented, including up to date results obtained from the T4B experimental campaign.  

CP11.00148: Statistical analyses of a highenergy ion transport on GAMMA 10/PDX Ryuya Ikezoe, Seowon Jang, Koki Izumi, Makoto Ichimura, Mafumi Hirata, Takumi Onchi A collisionless plasma with ion temperature perpendicular to a field line of several keV is produced by ion cyclotron heating and confined in a mirror filed on GAMMA 10/PDX. Highenergy ions transported along the field lines, which are dropped into a loss cone region in velocity space, are directly measured by several ion detectors at the machine end. These characteristics offer an excellent experimental environment for the study of wave particle interaction in velocity space. Ion detectors equip a semiconductor or a microchannel plate with a preamplifier, which convert an ion charge to a detectable current. The detection energy of ions can be varied by a cylindrical ion energy analyzer or multigrid electrostatic analyzer. Some intermittent and/or periodic behavior has been observed in detected ion current signals. The ion flux is not only a function of the mirror confined plasma density but also a function of characteristics of several waves and fluctuations. Statistical analyses are applied, and statistical characteristics hidden in a mirror trapping of highenergy ions is discussed.  

CP11.00149: Ion Cyclotron Resonant Heating in the Central Cell of the Keda Mirror with AXisymmetricity (KMAX) Xuan Sun We report the results of ion cyclotron resonance heating (ICRH) in the central cell of a fully axisymmetric tandem mirror. With a total power of 100 kW radiated by double halfturn (DHT) and halfturn (HT) antennas, the plasma diamagnetism increases by 15fold, with a corresponding peak beta ~2%, density ~ 2*10^18 m^3 , and total temperature ~60 eV. The effects of the magnetic configuration on resonance heating and wave emission are studied by varying the magnetic fields at the midplane and at the location of the antennas, respectively; the results confirm that the magnetic beach configuration is key to successful ICRF heating. The axial phase speed measurements suggest that the excited wave is a slow wave in the plasma core and a fast wave at the edge.  

CP11.00150: Device overview and first results from the gas dynamic trap prototype Marcel D. Granetzny, Jay K. Anderson, Mike Clark, Jonathan Green, Oliver Schmitz, Cary B Forest A new GDT inspired mirror experiment is under development at the University of Wisconsin at Madison for possible application as a beam driven neutron source. The gas dynamic trap (GDT) has shown remarkable results in recent years, with major improvements in electron thermal confinement and plasma stability at high beta. UWMadison is in a conceptual design phase for a GDT experiment for fusion research, basic plasma physics studies and as a costeffective neutron source. Envisioned neutron production rates range from 10^{15} to 10^{18} neutrons/sec. As a first development step our prototype uses 6 T HTS REBCO end mirror coils, developed in collaboration with GA, resulting in a mirror ratio of 20. The plasma is sustained using a helicon wave with a steady state power of 10 kW. Physics goals include demonstration of MHDstability in quasistationary conditions, suitable for NBI absorption (0.7 MW, 20 kV, 50 ms NBI into n_{e} ~ 5 x 10^{19} m^{3}, T_{e} ~ 200 eV plasma), electron temperature control, plasma rotation and biasing with LaB_{6} cathodes, NBI fueling and Li end wall pumping as well as understanding electron thermal confinement in the collisionless expander and the helicon dispersion relation in strong magnetic fields. First results will be presented.  

CP11.00151: Development of an axisymmetric mirrorbased neutron source using recent advances in technology Jay K. Anderson, Cary B Forest, Jan Egedal, Vladimir Mirnov, Ethan E Peterson, John Stephen Sarff, John P Wallace, Oliver Schmitz, Roger Waleffe, Robert Walter Harvey, Yuri Petrov We report an overview of work at the University of Wisconsin leading to a fusion neutron source based on axisymmetric mirrors, following along the Gas Dynamic Trap line of development. The design considers several recent physics and technological advances and uses offtheshelf MRI magnets for an inexpensive central cell, stateoftheart planar high field REBCO magnets and gyrotrons to allow high density operation. Improved performance is realized from sloshing ions (to localize neutron yield away from high field magnets), rf heating at the fastion turning points to enhance neutron yield, and a liquid lithium expanding diverter for heat removal, electron thermal barrier and MHD stability. Equilibrium, stability, and plasma heating scenarios have been modeled using a GradShafranov solver for the mirror including fast ion pressure coupled to the CQL3D/Genray suite of codes. We have been considering both paraxial and shortfat MHD optimizations of coil design. MHD stability is assessed using both energy principle calculations and ballooning mode eigenmode analysis. Initial results are very promising, with strong DD neutron yields (~10^{15}/s) with reasonable input power (40 MW).  

CP11.00152: Investigation of magnetic mirror configurations at the WiPPL facility and their applications Roger Waleffe, Ethan E Peterson, Jay K. Anderson, Mike Clark, John P Wallace, Cary B Forest The Wisconsin Plasma Physics Lab (WiPPL) has a unique flexibility to experimentally study various magnetic mirror geometries. Recently, two distinct types of mirror plasmas were made: one with axial current and one without. The former allows for confinement and stability properties to be explored and, further, may serve as a viable, cheap, simple fusion neutron source design. The latter allows for the creation of flux rope turbulence important for studying coronal loop heating. Axial current can additionally provide a mirror plasma with high beta turbulence or one that can serve as a plasma target for reconnection experiments. Initial data gives mirror plasmas as dense as 2x10^{19} m^{3} with 8eV electrons/ions and betas ranging from 0.1 to 10. WiPPL has also performed a number of numerical calculations for plasma stability in mirrors. Specifically, nonparaxial (spherical) mirrors are predicted to stabilize the m = 1 flute mode due to their favorable curvature. Further analysis in the ballooning approximation has shown stability with respect to highm modes. Future nonparaxial mirror experiments at WiPPL will hope to confirm these stability properties. Magnetic mirrors improve confinement and provide a great base plasma for studying reconnection, turbulence, and stability.  

CP11.00153: Low inductance high voltage multigap gas switch for high repetition rate pulsed power applications Adam J Klim, John T Morrison, Gregory K. Ngirmang, Joe Smith, Kevin M George, Joseph C Snyder, Enam A Chowdhury, Kyle Frische, William M Roquemore The ability to perform high repetition rate pulsed power experiments depends crucially on several factors including fast switching and fast power supply charging times. We present the design from operation of the switch used for a 10Hz fast dense plasma focus experiment to be conducted at the Air Force Research Laboratory at the WrightPatterson Air Force Base. More importantly, due to the relatively simple design with low cost for parts, modifications such as changes to the internal air pressure or the electrode size can be easily made to increase the versatility of the switch. Furthermore, we will demonstrate how the use of annular electrodes can be a better alternative to the conventional solid disk electrodes by the reduction of inductance from the formation of a cylindrical plasma current carrying sheath and overall switch weight.  

CP11.00154: Discovery and characterization of a population of Fermilike accelerated electrons from an electrostatic oscillation in the PFRCII run as a lowpower tandem mirror Charles Swanson, Tony Qian, S. A. Cohen Using Silicon Drift Detector (SDD) Xray pulseheight spectrometers and Langmuir probes, we have discovered a population of electrons with an effective temperature of 3 keV and individual electrons above 30 keV in the PFRCII device when run as a lowpower tandem mirror. These electrons have density around 10^8/cm^3 vs bulk density 10^11/cm^3 and temperature ~5 eV. We have detected an electrostatic oscillation, ~100 MHz and ~10 V, at a mirror nozzle of the central cell, proposed to be caused by a spontaneously generated beam of electrons entering this cell. Like the apparatus of Alexeff et. al. in the 1960s and current experiments on the GOL3 mirror machine, this beaminduced fluctuation causes heating of electrons. These machines were assumed to break resonance boundaries and cause electrons to become stochastic via a turbulent wave spectrum. In the PFRCII, our calculations indicate the effect is caused by a Fermilike acceleration. They indicate that mirrorbounce motion combined with a small potential fluctuation is sufficient to break resonances and cause stochastic electron motion. Magnetic moment nonadiabaticity is essential.  

CP11.00155: The TenYear Evolution of a HighPower Magnet Driver Kenneth E Miller, Timothy Ziemba, James R Prager, Ilia Slobodov Eagle Harbor Technologies, Inc. (EHT) initially began the development of high current solidstate switching topologies over a decade ago. Since then EHT has developed multiple solidstate power systems for use in applications ranging from fusion energy science to medical devices. The Integrated Power Module is a high current switch was first developed in 2008 as part of an DOE Fusion Science SBIR program for solid state inductive current driving. This switch is capable of continuous operation at several kilowatt output powers and pulsed operation at MW peak powers. Since the early development, this power system has undergone several major upgrades including the addition of heat sinking to allow for continuous wave (CW) operation. Here we will present the evolution of the system design over the last decade. We will also present capabilities ranging from single pulse characteristics; highfrequency, high current switching, and CW operation.  

CP11.00156: FuZE Compact Fusion Device  Outlook for Scaling up to Reactor Conditions H S McLean, U Shumlak, B A Nelson, D P Higginson, E L Claveau, E G Forbes, R P Golingo, J M Mitrani, A E Schmidt, A D Stepanov, K K Tummel, T R Weber, Y Zhang The University of Washington and Lawrence Livermore National Laboratory have partnered to advance the shearedflow stabilized (SFS) Zpinch concept and assess its potential for scaling to fusion conditions. The Fusion Zpinch Experiment (FuZE) expands on UW's ZaP and ZaPHD SFS devices by employing higher powerhandling electrodes along with flexible gas injection and power systems that tailor the discharge current and distribution of gas to establish the required plasma flow and pinch current. An extensive set of diagnostics provide key measurements. We are executing experimental campaigns to increase the pinch current, duration of pinch stability, and DD fusion neutron production guided by both fullykinetic and fluid based computer simulations. These efforts aim to scale this concept to high current, plasma density, and temperature with a goal of demonstrating a practical path to a compact, lowcost fusion reactor.  

CP11.00157: Implementation of an eightcord equal path length, heterodyne interferometer on the Fusion Zpinch Experiment FuZE Y. Zhang, J. Barhydt, R. P. Golingo, B. A. Nelson, U. Shumlak, K. K. Tummel, D. P. Higginson, H. S. Mclean The Fusion ZPinch Experiment (FuZE) project uses a radialsheared axial flow stabilized Zpinch to develop a compact fusion device. The machine is able to drive ~ 200 kA of pinch current, compressing the pinch to a radius of ~ 3 mm. By seeding the hydrogen Zpinch with a minority concentration of deuterium, thermal fusion neutrons are produced. An extensive set of diagnostics provide key measurements, including an eightcord equal path, heterodyne, quadrature phase differential interferometer. Three chords are located at acceleration region to investigate the snowplow and deflagration processes for longlived Zpinch structures. Five chords are located at the midplane of the 50 cm Zpinch assembly region with 1 cm vertical spacing to measure the evolution of plasma density profile. Assuming cylindrical symmetry, Abelinverted radial density profiles are reconstructed from these fivechord lineintegrated electron density data. Furthermore, assuming a constant drift speed, the temperature profile is calculated and compared with ion Doppler spectroscopy measurement. The design of the interferometer and detailed data analysis will be presented.  

CP11.00158: Experiments and Modeling of Current Sheet Dynamics in a Coaxial Plasma Accelerator on the FuZE Experiment A.D. Stepanov, U. Shumlak, R.P. Golingo, Y. Zhang The FuZE experiment produces shearedflow stabilized Zpinch plasmas with lifetimes of 10s of μs, ~keV ion temperatures, and densities of ~10^{16}10^{17} cm^{3}. FuZE consists of a 1m coaxial plasma accelerator that injects plasma into a 0.5 m long assembly region, where a pinch is formed with an embedded axial flow. Since pinch lifetime is set by the duration of plasma flow from the accelerator, maximizing the latter is desired. The structure of the current sheet is reconstructed from a longitudinal magnetic probe array that measures the azimuthal magnetic field profile B(z,t) with 5cm spatial resolution. The initial snowplow phase of the current sheet is welldescribed by a 1D resistive MHD model. The calculated plasma density, velocity, and temperature profiles are compared to available experimental measurements. The deflagration phase of the discharge in the accelerator, which is responsible for longduration plasma injection into the assembly region, is not captured by the simple MHD model. Several hypotheses to explain the deflagration mode are analyzed, including impedance mismatch between the accelerator channel and the assembly region, and complex plasmaneutral interaction effects, such as charge exchange.  

CP11.00159: Increasing neutron production in the FuZE experiment by optimizing the neutral fill profile and the current waveform. Raymond Golingo, Uri Shumlak, Brian A Nelson, Elliot L Claveau, Eleanor G Forbes, Anton Stepanov, Tobin R Weber, Yue Zhang, Harry Scott McLean, Drew P Higginson, James M Mitrani, Andrea Elizabeth Schmidt, Kurt Tummel Sheared flow stabilized Zpinches can be an economical path towards fusion energy. The FuZE experiment at the University of Washington is investigating the viability of this concept. The device uses a single power supply and two coaxial electrodes to form, compress, and sustain a sheared flow Zpinch. The electrodes are divided into an acceleration and assembly region. The acceleration region initially operates in a snowplow process, with an accelerating current sheet ionizing neutral gas ahead of the sheet. The accelerator then transitions into a deflagration type ionization process, where neutral gas behind the current is ionized and accelerated towards the assembly region. The snowplow type process forms the shearedflow Zpinch and the deflagration process maintains a stable Zpinch. The neutron production in a stable Zpinch can be optimized through tailoring of the neutral gas profile in the acceleration region. Characterization of these processes and the use of these processes to optimize and extend the neutron production in FuZE will be presented.  

CP11.00160: High resolution digital holographic interferometry on the Fusion Zpinch Experiment FuZE Tobin Weber, Uri Shumlak, Brian A Nelson, Elliot L Claveau, Eleanor G Forbes, Raymond Golingo, Anton Stepanov, Yue Zhang, Harry Scott McLean, Drew P Higginson, Andrea Elizabeth Schmidt, Kurt Tummel The Fusion ZPinch Experiment (FuZE) is a sheared flow stabilized (SFS) Zpinch experiment investigating the scaling of SFS Zpinch plasmas towards fusion conditions. Sustained neutron production has been measured from cylindrical plasmas of high density (> 10^{17}/cm^{3}), high temperature (> 1 keV), and small radii (< 5 mm) [1]. Diagnosing the size, density and internal structure of these plasmas require a high spatial resolution plasma density diagnostic. Motivated by this, a holographic interferometer with 10 micron spatial resolution has been installed on FuZE [2]. A Nd:YAG laser is used with a digital camera to produce holograms from the plasma assembly region. Digital holograms are numerically reconstructed to obtain the chordintegrated electron density of the compressed plasma, with fine spatial resolution. Assuming cylindrical symmetry, radial density profiles are reconstructed from electron density data. Radial temperature profiles are calculated by assuming radial force balance, and uniform plasma drift velocity. Chordintegrated density, radial density and radial temperature data are presented from FuZE. [1] Y. Zhang et al., PRL, Manuscript submitted for publication. [2] M.P. Ross & U. Shumlak, RSI 87, 103502 (2016).  

CP11.00161: Timeresolved Spectroscopy for Temperature Profile Measurements of a Sheared Flow Stabilized ZPinch Eleanor G Forbes, Uri Shumlak, Brian A Nelson, Elliot L Claveau, Raymond Golingo, Michal Hughes, Michael P Ross The ZaPHD Flow Zpinch device is designed to scale the sheared flow stabilized Zpinch to high energy density conditions. ZaPHD uses a triaxial electrode configuration to decouple formation and compression power for a 50 cm long, 0.4 cm diameter hydrogen pinch. Plasma conditions can exceed temperatures of 1 keV and densities of 2e17 cm^{3}, with lifetimes of 100 μs. The device is being used as a platform to develop a novel spatiotemporally resolved diagnostic to measure plasma temperatures throughout the pulse. ZaPHD uses ion Doppler spectroscopy (IDS) to obtain radial profiles of temperature and velocity by measuring the emission profiles of carbonIII and carbonV. The IDS system uses a detector which is only capable of making one measurement per plasma pulse. Acquiring timeresolved profiles requires data collection at varying times over hundreds of pulses. To reduce the number of pulses needed to characterize the plasma conditions, a spectrometer is coupled to a Kirana ultrafast framing camera to obtain up to 180 spectra at rate of 5e5 frames/s throughout the plasma lifetime. These data can elucidate the continuous evolution of the temperature profile at one axial location in the pinch from a single plasma pulse.  

CP11.00162: Temporally and spatially resolved measurements of neutron production in a shearedflow stabilized (SFS) Zpinch*. James Mitrani, Drew P Higginson, Christopher M Cooper, Kurt Tummel, Andrea Elizabeth Schmidt, Harry Scott McLean, Zack Draper, Elliot L Claveau, Eleanor G Forbes, Raymond Golingo, Brian A Nelson, Anton Stepanov, Tobin R Weber, Yue Zhang, Uri Shumlak, Jonathan T Morrell, Lee Allen Bernstein, Karl Albert Van Bibber Neutron yields >10^{5} per shot, with burn durations >5 μs, were measured on a shearedflow stabilized (SFS) Zpinch fueled with 20% partial pressure of D2 in a background gas of either H2 or He, for several operating conditions. Shearedflow stabilization requires establishing a radiallysheared, axial plasma flow which limits growth of sausage (m=0) and kink (m=1) instabilities [1], and allows the pinch to persist in quasisteady state conditions for many radial Alfven transit times. Measured neutron production appears to occur in quasisteadystate conditions, consistent with thermonuclear fusion. Multiple detectors are used to constrain the location and length of neutron production within the plasma. Neutron energies are analyzed by measuring the energy spectra of recoil protons in fast plastic scintillators. Detailed results will be presented. [1] – U Shumlak and CW Hartman. Phys. Rev. Lett. (1995) 75(18):3285.  

CP11.00163: Fusion space propulsion system based on the sheared flow stabilized Zpinch Uri Shumlak, Behcet Acikmese, Elliot L Claveau, Eleanor G Forbes, Raymond Golingo, Brian A Nelson, Yue Zhang Thermonuclear fusion provides a large energy release per reactant mass, and offers a solution for rapid deep space propulsion if a configuration can be developed with a small system mass. Many magnetic confinement configurations require large magnetic field coils to stabilize the plasma at the expense of lower beta and higher system mass. The Zpinch has no magnetic field coils and unity beta; however, it is unstable to MHD modes. The sheared flow stabilized (SFS) Zpinch uses axial flows to provide stability, has demonstrated an ability to confine plasmas to fusion conditions without magnetic field coils, and promises a compact fusion concept with Q>1. An SFS Zpinch fusion space propulsion system presents unique spacecraft control challenges: controlcentric modeling including dynamics, state and control constraints; offline and online minimum fuel/time trajectory design and redesign; and robust and accurate trajectory tracking. Building on the ZaP, ZaPHD, and FuZE projects, scaling studies will be presented of an SFS Zpinch as a fusion space thruster, which generates high exhaust velocities (~10^{7} m/s) and high thrust (~10^{6} N) with low system mass, as will be shown through calculations that account for input power, repetition rate, and duty cycle.  

CP11.00164: Characterization of Electron Beams from a Dense Plasma Focus Emil E. Petkov, Stuart L Jackson, Arati Dasgupta, Nicholas David Ouart, John L Giuliani The study of electron beam generation in a dense plasma focus (DPF) can yield insight into the physical mechanisms which lead to the formation of electron beams in pinched plasmas. A detailed understanding of these mechanisms may enable the production of a highintensity xray source for various applications. Plasma polarization spectroscopy (PPS) is a novel diagnostic tool which will be employed in this proposed work to investigate the electron distribution function and fields within a DPF plasma. PPS relies on coupling sophisticated atomic and ionization modeling with emission data obtained with a specially designed spectropolarimeter. We plan to use PPS to measure the degree of polarization of several xray spectral lines emitted by a DPF driven by NRL’s Hawk pulsedpower generator. The measured degree of polarization will then be compared with atomic and radiation calculations for different electron distribution functions in order to diagnose the electron beam and infer the strength of the accelerating electric field in the DPF.
 

CP11.00165: Modeling of the hawk dense plasma focus (DPF) device using USIM Christine M. Roark, Peter H. Stoltz, John W. Luginsland, Stuart L. Jackson, John L. Giuliani, Joseph T. Engelbrecht, A. Stephen Richardson, Joseph W. Schumer, Andrey Beresnyak We compare MHD simulation results to experimental measurements taken from a dense plasma focus driven by the HAWK pulsedpower generator (0.65 MA peak current, 1.2 μs rise time). USim is a 3D capable, fluid plasma modeling framework that simulates the dynamics of charged fluids using the ideal MHD equations, among others. The DPF device is modeled using an unstructured mesh, and initial conditions are applied to account for plasma injected radially inward by 3 Marshall guns, as well as additional mass injected by an onaxis gas puff valve. The nonaxisymmetric nature of the Marshall guns means that full 3D simulations are required, though 2D simulations are compared as well. The initial conditions were varied to determine their effect on the pinch. Simulated current, voltage, inductance and neutron yield are compared with experimental results. We also calculate simulated xray and optical images of the plasma and compare with experiment.  

CP11.00166: Overview of Progress on the NRL Dense Plasma Focus Program Andrew Richardson, Stuart L Jackson, Joseph T Engelbrecht, Andrew Y Jiao, Andrey Beresnyak, John L Giuliani, Bruce V Weber, Emil E. Petkov, Joseph W Schumer, Daniel Klir, Karel Rezac, Jakub Cikhardt, Yitzhak Maron, Evgeny Stambulchik, Christine Roark, Peter Stoltz, Anton Spirkin, John W Luginsland A dense plasma focus (DPF) experimental and modeling program has recently started using the Hawk pulsedpower generator at the Naval Research Laboratory (NRL), which is a highinductance (607 nH) generator with a rise time of 1.2 μs and a peak current of 650 kA into a DPF load. In this poster we give a status update of the project, with an overview of both the experimental and modeling results. This overview includes experimental results of interferometric density measurements, xray pinhole images of the pinch, neutron yield measurements, ionpinhole diagnostic results, and preliminary xray spectral measurements. The modeling results include 2D and 3D MHD simulations of the DPF as well as an investigation into the effect of various fluid model approximations on the development of the m=0 pinch instability.  

CP11.00167: Design of a MegajouleClass Dense Plasma Focus as a Flash Neutron Source At LLNL Alexander Povilus, Rick Anaya, Michael Gordon Anderson, Steve Chapman, Christopher M Cooper, Steve Falabella, Clement S Goyon, Drew P Higginson, Ihor Holod, Edward S. Koh, Anthony J. Link, James M Mitrani, Aric Pearson, Yuri A Podpaly, Dave Van Lue, James Watson, Andrea Elizabeth Schmidt The MegaJOuLe Neutron Imaging Radiography (MJOLNIR) experiment is an approximately 3MA (upgradable to 4.5MA) dense plasma focus (DPF) that has been designed and is currently being constructed at LLNL. The goal of the device is to produce an intense, flash source of neutrons for radiography applications. The device will leverage recent results from both LSP hybrid fluid/kinetic simulations and smaller scale DPF’s at LLNL. These modifications include improvements to conventional DPF designs such as advanced anode geometries, modified insulator geometry vacuum chamber/electrodes removable as a sealed unit, and an improved diagnostic package. Here, we present an overview of the current device design, including progress made in prototyping and constructing the device. We also report on status of first plasmas.  

CP11.00168: The suite of diagnostics for the new MJ Dense Plasma Focus Device at LLNL Clement S Goyon, Christopher M Cooper, Steve S Chapman, Drew P Higginson, Anthony J. Link, Edward S. Koh, Yuri A Podpaly, James M Mitrani, Alexander P Povilus, Rahul R Prasad, Brian Shaw, Andrea Elizabeth Schmidt In a Dense Plasma Focus (DPF), a high voltage is pulsed across a lowpressure gas between coaxial cylindrical electrodes. The gas is ionized and magnetically compressed to form a highdensity (several 10^{21} cm^{3}) plasma (the pinch) at the tip of the central electrode. During the pinch, magnetic instabilities generate electric fields that can accelerate ions up to several MeV. These ions produce neutrons via beamtarget interaction with the dense plasma present onaxis. We present the suite of diagnostics implemented on the new MegaJoule class DPF (MJOLNIR, Povilus et al.) built at the Lawrence Livermore National Laboratory, and first measurements from these diagnostics. We describe measurements of neutron yields using lanthanum bromide and beryllium realtime neutron activation detectors. Rogowskibased current measurements and optical images of the plasma sheath before and during the pinch. Additionally, measurements from neutron timeofflight detectors, light diode detectors that measure plasma sheath timing and symmetry, and an optical spectrometer will be shown. Designs for future diagnostics, including an interferometer to measure plasma density and an ion energy spectrometer will be discussed.  

CP11.00169: Increasing neutron yield and minimizing copper sputter by varying the diameters of a DPF hollow anode Brian H. Shaw, Steve Chapman, Christopher M Cooper, Clement S Goyon, Andrea Elizabeth Schmidt Experiments were performed to maximize neutron yield from a dense plasma focus (DPF) and characterize the amount of copper sputtered from the surface of an anode by varying the diameter of the anode's onaxis hollow. These experiments were performed at Lawrence Livermore National Lab on a kJclass DPF. All of the anodes with a hollow produced greater yields per discharge than anodes without a hollow. The largest average yield produced (9.1+/0.4x10^{6} neutrons per discharge) was 6.2 times higher than the average yield with no hollow, and the data suggest an optimal hollow diameter. Qualitative differences in surface damage were seen on each anode and quantitative measurements were performed by measuring the copper sputtered onto onaxis quartz targets for three newly machined anodes of varying hollow diameters.  

CP11.00170: Improvements in Pinch Formation Using Tapered, Hollowed Anodes in a MJClass Dense Plasma Focus Drew P Higginson, Anthony J. Link, Ihor Holod, Dale R Welch, Andrea Elizabeth Schmidt A dense plasma focus (DPF) device drives current through a set of coaxial electrodes to assemble plasma inside the device and implode the plasma on axis to form a Zpinch. The implosion drives instabilities to generate strong electric fields, which produce short intense pulses of xrays, highenergy (>100 keV) electrons and ions, and if using fusionreactant ions (e.g. D, T), will generate neutrons. As well as being dependent on the highenergy ion “beam”, neutron production relies on the formation of a long, highdensity, “plasma target” that the ions will pass through. Using the particleincell code Chicago in 2D3V, we simulate the plasma target formation in a multimegaamp DPF device. We find that adding a taper and a hollow to the inner electrode (anode) improves the formation of the plasma target on axis by creating a more uniform implosion. The taper is most helpful for large radius anodes and is a potential method for mitigating yield rolloff at high currents (3+ MA). We investigate the importance of the electron temperature of the plasma target on the ion stopping power to understand the optimization of the anode shape. We also describe how to achieve a given neutron yield based on estimates of the ion beam & plasma target.  

CP11.00171: Optimizing Dense Plasma Focus Neutron Yields with Fast Gas Jets Matthew McMahon, Elizabeth Stein, Drew P Higginson, Ihor Holod, Anthony J. Link, Andrea Elizabeth Schmidt We report on a study using the particleincell code Chicago to perform fully kinetic simulations of dense plasma focus (DPF) devices with patterned gas loads created via supersonic gas jets on axis. The supersonic jets are modeled in the largeeddy NavierStokes code CharlesX, which is suitable for modeling both subsonic and supersonic gas flow. The gas pattern, which is essentially static on zpinch time scales, is imported from CharlesX to Chicago for neutron yield predictions. Fast gas jets allow for manipulating the mass on axis while maintaining the optimal background pressure for the DPF. The conditions favorable for producing neutrons are found to be more consistently met when a jet is present on axis. Perturbations in the jet density introduced via supersonic flow (known as Mach diamonds) allow for consistent seeding of the m=0 instability, producing a better ion beam, and consistent target formation leading to more consistent ion acceleration and higher neutron yields with less variability. The optimal jet configuration for increasing neutron yield and reducing shottoshot yield variability is explored.  

CP11.00172: Kinetic Simulations of Gas Breakdown on MJscale Dense Plasma Focus Device Anthony J. Link, Justin Ray Angus, Drew P Higginson, Andrea Elizabeth Schmidt Dense plasma focus (DPF) Zpinches are compact pulse power driven devices with coaxial electrodes. The discharge of DPF consists of three distinct phases: first generation of a plasma sheath, plasma rail gun phase where the sheath travels down the electrodes and finally an implosion phase where the plasma stagnates into a zpinch geometry. The plasma on axis rapidly goes unstable and can produce a short, intense pulses of fast ions and neutrons when deuterium is used as the working gas. The magnitude of the neutron yields produced scales strongly with the current delivered to the pinch. Preventing parasitic current pathways, which can be generated at each stage of the DPF discharge, is critical to getting high neutron yield. The most straightforward source of parasitic current pathways is incomplete breakdown or poor liftoff of the plasma sheath during the early stage of the discharge. This work is focused on understanding the dynamics of the initial plasma sheath using fullykinetic simulations with the particleincell (PIC) code LSP for a MJscale DPF in an axisymmetric geometry with deuterium. Effects of varying the electrode geometry, initial gas fill and driving voltage will be presented.  

CP11.00173: Density and Temperature Measurements on the Microsecond XPinch Georges S Jaar, Richard K Appartaim Several comprehensive experimental measurements have been conducted on the microsecond xpinch. First, a twoframe MachZehnder interferometer has been implemented for electron density measurements via a frequency doubled, pulsed Nd:YAG laser. The second frame is delayed from the first by 61 ns, which allows for sameshot time evolution dynamics to be observed. The measurements presented on the axial plasma jets complement previous schlieren imaging results. Secondly, timeintegrated xray spectroscopy has been conducted with a flat crystal spectrometer and xray sensitive film. Results from aluminum xpinches have demonstrated the presence of He and Hlike ionic states, allowing a determination of the electron temperature of the hot spots. Further results on the spectroscopy of other wire materials will also be presented. Lastly, a study of load optimization for xray yield on the microsecond pinch will also be presented.  

CP11.00174: Lumped versus detailed accounting for dielectronic recombination processes in nonLTE kinetics of a copper pinch Nicholas David Ouart, Arati Dasgupta, John L Giuliani, Emil E. Petkov, Robert Clark The NRL DZAPP code has been used to simulate a copper z pinch. DZAPP couples 1D MHD with nonLTE level kinetics and radiation transport, and incorporates a transmission line circuit to drive the load. The nonLTE level kinetics in DZAPP is solved using an atomic model that includes dielectronic recombination as an effective lumped groundtoground rate with radiative transport equation using a frequency averaged probabilityofescape method for the lines and edges. The plasma profiles of density and internal energy will also be postprocessed with the NRL code Drachma II. The nonLTE model in Drachma II is more general. First, the doubly excited state populations are explicitly carried in the level kinetics. Consequently, the satellite lines are inherently generated in the synthetic spectrum. Second, line overlap is automatically included because of the treatment of multifrequency radiation transport. The resulting differences in the ionization balance and synthetic spectra between the two approaches will be presented for the L and Kshell of copper.  

CP11.00175: Simulations of GasPuff ZPinch Implosions with comparison to Magnetic Fields measurements at the Weizmann ZPinch. Varun Tangri, John L Giuliani, Guy Rosenzweig, Tal Queller, Eyal Kroupp, Yitzhak Maron Measurements of magnetic field in gaspuff implosions on the generator at the Weizmann Institute of Science (WIS) have been recently shown to be in contradiction to a snowplow model using the current of the pulsedpower generator and the pinch radius. Simulations of magnetic field evolution using the 2D radiationmagnetohydrodynamic code, MACH2TCRE are presented in two steps as follows. In the first step, simulations of the initial density profile by modeling the neutral gasflow of subsonic oxygen through DeLaval nozzles are made and compared to measurements. In the second step, the density profiles from the previous step are used as initial conditions for investigating the distribution evolution of the magnetic field during the gaspuff implosions. Comparisons are made with the measured data of magnetic field and radius. It is shown that simulating the nozzle geometry and outflow significantly improves the comparison between the measurements and the pinch simulations.  

CP11.00176: Diagnostics of MultiMeV Ions Produced in Deuterium ZPinch Experiments on GIT12 Generator K. Rezac, V. Munzar, D. Klir, Jakub Cikhardt, P. Kubes, J. Kravarik, B. Cikhardtova, A. V. Shishlov, V. A. Kokshenev, R. K. Cherdizov, N. A. Ratakhin, K. Turek Hydrogen ions with energies >30 MeV were measured in deuterium zpinch experiments on the GIT12 generator (600 kV output voltage, 3 MA current level) by different diagnostics during several experimental campaigns since 2013. The annular structures were firstly observed by single ion pinhole camera placed on zpinch axis behind the cathode. The stack of detectors contained various absorbers, CR39 track detectors, HDV2 and EBT3 radiochromatic films. However, this diagnostic could not explain all results. Therefore, the new types of ion diagnostic (beam profile detector, 3pinhole, multipinhole, linearmultipinhole) were designed for a study of fast ion beams from wide angles from a zpinch axis. Obtained data together with numerical simulation help us to (i) find a spatial distribution of ion sources in radial and axial directions and (ii) study of the anisotropy and the divergence of the ion beams.  

CP11.00177: Conceptual design of a compact pulsed power generator for staged Zpinch experiments David Reisman, Hafiz Rahman, Paul Ney, Emil Ruskov, Jeff Narkis, Farhat N Beg We have developed the conceptual design of a 500 kJ pulsed power accelerator, called LTDX. This highly efficient generator, based on linear transformer driver (LTD) technology, will enable fusion experiments to be performed using staged Zpinch (SZP) loads. Five modules, each consisting of five cavities connected in series, transport current to a central vacuuminsulated power flow section and load. Each cavity consists of 20 capacitorswitch units called “bricks” which, owing to their circuit parameters, provide a characteristic 100 ns current rise time without the need of pulse compression. The resulting system, which exploits impedance matching between elements, can produce a peak current of 67 MA with an energy delivery efficiency to the load of approximately 30%. We will discuss the integrated use of circuit, 3D electromagnetic, and magnetohydrodynamic (MHD) codes to obtain a highfidelity generator design. We will also discuss SZP loads optimized for the LTDX generator using the MACH2, TRACII, and HYDRA MHD codes.  

CP11.00178: Staged Zpinch experiments at the 1MA Zebra pulsed power generator using Krliner and CuW nozzle and cathode Emil Ruskov, Hafiz Rahman, Fabio Conti, Julio Valenzuela, Nicholas Aybar, Jeff Narkis, Farhat Beg, Eric Dutra, Aaron Covington In these experiments a krypton liner is compressing deuterium target while the plasma column is stabilized with external axial magnetic field B_{z} = 0.51.5 kG. The cathode and the gas injection nozzle erosion is minimized by using coppertungsten alloy. Multispoke and honeycomb cathodes are used, with the later providing more consistent pinches. The pinch stability is monitored with two quad Xray pinhole cameras. The fusion neutrons are diagnosed with silver activation diagnostics, neutron bubble detectors and four time of flight detectors (nTOF). Consistently high neutron yields in the ~510 x10^{9} range are measured and their thermonuclear origin is suggested by data from a pair of horizontally and vertically placed nTOFs. The eight frame Xray pinhole camera images confirm the staged Zpinch stability.  

CP11.00179: Experiments and Simulations of staged ZPinch on 1MA ZEBRA facility Hafiz Rahman, Emil ur Ruskov, Paul Ney, Fabio Conti, Julio Valenzuela, Jeff Narkis, Nicholas Aybar, Farhat N Beg, Eric Dutra, Aaron Covington Experiments at ZEBRA show uniform compression of a deuterium plasma target compressed by a highZ gaspuffed liner like Ar or Kr. Pinch stability is improved by seeding the implosion with 0.050.15T of B_{Z}. Implosion dynamics are also studied computationally with MACH2 & HYDRA codes. Simulations show that magnetic field diffuses through the outer shell and piles up at the interface providing narrow profile of high intensity current that preheats the target. This secondary piston launches shock waves in target plasma that heats the target to several hundred eV and this preheated target plasma is adiabatically compressed to densities up to 5x10^{20} cm^{3} and temperature of 510KeV. Simulations show more pronounced preheating with Kr than Ar. Axial magnetic field is compressed only in the shocked target and in the liner plasma, providing greater MRT mitigation. For Ar liner on D target experiments we measured neutron yield of 25x10^{9} and for Kr liner 512x10^{9}. Experimental observations like plasma current, visible streak images, gatedXUV pinhole images, and laser shadowgraphs are compared with simulations, and show general agreement. The experimentally measured neutron yield is also in good agreement with simulations.  

CP11.00180: HEDP experiments on a 0.8 MA LTD generator at UCSD Fabio Conti, Julio Valenzuela, Michael Ross, Nicholas Aybar, Jeff Narkis, Emil Ruskov, Hafiz Rahman, Farhat Beg Linear Transformer Drivers (LTDs) are the most promising highcurrent pulse generators, as they offer several advantages over Marx bank based systems: small footprint, more efficient energy coupling to the load, possible multistage modularity, and potential for higher repetition rate.  

CP11.00181: Modeling lowdensity regions in power flow experiments using MHD codes William Anthony Farmer, Charles L Ellison, George B Zimmerman, Nathaniel D Hamlin, Charles E Seyler, James Henry Hammer, Keith Lechien Lowdensity regions are difficult to model in traditional MHD, singlefluid codes. First, the classical Spitzer resistivity is independent of density so that in extrapolating toward vacuum, the Ohmic current is carried by fewer charge carriers moving at unrealistic speeds. Additional physics such as the Hall term or lowerhybrid drift turbulence can lead to an effectively larger resistivity which enhances diffusion of the magnetic field. Traditionally, this hardertomodel physics is crudely approximated by the use of a density floor below which the resistivity is arbitrarily increased to some large value in an ad hoc approximation of the vacuum. Here, we demonstrate how differing treatments of the vacuumtoplasma transition can lead to qualitatively different behavior in simulations. This is done in the context of a coaxial transmission line pulsed with 20 MAmps of current over 100 ns [1] to capture physics relevant to the magnetically insulated transmission lines (MITLs) on Sandia’s Z pulsed power facility. [1] N. D. Hamlin and C. E. Seyler. Submitted to Phys. Plasmas (2018).  

CP11.00182: Planar Shock Wave Propagation in MultiSpecies Gas with a 200kA Pulsed Power Driver Nicholas Aybar, Fabio Conti, Julio Valenzuela, Farhat Beg Shock waves in multispecies gases are relevant in a variety of topics in high energy density physics including astrophysical plasma physics and inertial confinement fusion (ICF) especially in linerontarget implosion schemes. Results from planar foil shock experiments on a 200kA pulsed power driver, GenASIS, are presented. In this experimental setup, a 5×5 mm^{2} foil load of 110 μm thickness is heated and ablated by a high current pulse. The material is then accelerated normal to the foil plane via a magnetic pressure gradient set up by the anodecathode gap. The characteristics of foil expansion and motion are initially studied by diagnosing the accelerating material in vacuum to determine the effect of foil load parameters on performance. Ablated material motion, as well as shock velocity, is determined using a fourframe schlieren imaging system with 30 ns interframe delay on an Nd:YAG laser. The relative motion of gas species is measured using spatially resolved visible spectroscopy coupled to a twoframe gated ICCD camera with 1 μs interframe interval.  

CP11.00183: At ignition scale experiments on NIF of next generation MagLIF laser preheat Michael E. Glinsky, Matthew R. Weis, Kyle J. Peterson, David J. Strozzi, Bradley B. Pollock, John D. Moody, Clement S. Goyon, Adam Sefkow Development of a cryogenic and magnetized gas pipe platform is underway at NIF. Experiments have been done into unmagnetized, room temperature, hydrocarbon and cryogenic D2 gases of densities that span 1.6 mg/cc to 4.8 mg/cc (5% to 16% critical electron density). 30 kJ of energy from one quad have been delivered into a oval spot of 1580 micron mean diameter over a time of about 11 ns with a power 2 TW and an intensity of 2x10^{14 }W/cm^{2}. A large fraction of the laser energy has been absorbed by Inverse Bremsstrahlung absorption over the 1 cm length of the gas pipe. Temperatures of up to about 1300 eV have been reached in the core. Raman and Brillouin backscatter were measured to be "low" on all shots. Experiments in FY19 are planned that will apply a magnetic field of up to 30 Tesla along the axis of the laser deposition for warm hydrocarbons. Applying a magnetic field to the cryogenic D2 gas is possible in future years. These experiments are focused on doing "to ignition scale" Magnetized Liner Inertial Fusion (MagLIF) laser preheat experiments for the next generation pulse power machine.  

CP11.00184: Favorable Collisional Demixing of Ash and Fuel in Magnetized Inertial Fusion Ian E Ochs, Nathaniel J Fisch Magnetized inertial fusion experiments are approaching regimes where the radial transport is dominated by collisions between magnetized ions, providing an opportunity to exploit effects usually associated with steadystate magnetic fusion. In particular, the lowdensity hotspot characteristic of magnetized liner inertial fusion (MagLIF) results in diamagnetic and thermal frictions which can demix thermalized ash from fuel, accelerating the fusion reaction. A simple diffusion model shows that increases in the fusion energy yield on the order of 510% are in fact possible. Our results could also be relevant for magnetic target fusion. Effects due to pressure anisotropy may also be discussed.  

CP11.00185: Investigation of flowdominated plasma interactions T. E. Weber, C. S. Adams, D. R. Welch, D. Rose, G. A. Kagan, I. A. Bean, M. D. Sherburne Pulsed acceleration of a plasma using a series of preciselytimed magnetic coils can enable attainment of velocities at which the kinetic energy exceeds the thermal and magnetic energy content of the flow. Interactions of these flowdominated plasma with other plasmas, neutral gases, magnetic fields, and/or solids, can convert kinetic energy to other forms, such as thermal or nonthermal/highenergy populations, enhanced magnetic fields, and radiation. The details of the stagnation process and final energy partition can vary greatly depending on the Magnetosonic Mach number, Knudesn number, Hall parameter, and plasma beta. Through experiment, theory, and simulation, we are developing an understanding of the physics of flowdominated plasma interactions, which has wideranging significance in basic plasma science and astrophysics, as well as applications such as magnetoinertial fusion and radiation science. Ongoing work includes developing new pulsed power systems, novel highspeed optical diagnostics, and exploration of new numerical techniques to specifically model the unique physics of translating/stagnating flowdominated plasma.  

CP11.00186: Extended MHD in the Ares multiphysics code Charles Leland Ellison, William A Farmer, James Henry Hammer, Keith Lechien, George B Zimmerman The Ares multiphysics code models a variety of processes relevant to highenergydensity systems, including radiation hydrodynamics, laser energy deposition, thermal conduction, atomic physics, themonuclear burn, and magnetohydrodynamics (MHD). Pulsed power experiments provide a demanding setting for multiphysics codes, requiring accurate models for soliddensity, roomtemperature materials and lowdensity, hightemperature plasmas. To improve the fidelity of the lowdensity plasma treatment, Hall MHD has been implemented in the 2D MHD package in Ares. The algorithm and implementation have been benchmarked using a Hall drift wave problem [J. D. Huba, Space Plasma Simulation, Springer (2003)]. The Hall term introduces shorttimescale oscillations that can drastically limit the numerical timestep when modeling pulsed power experiments. To mitigate these impacts, a combination of algorithmic modifications and subcycling have been implemented. This presentation will focus on these and other improvements to the treatment of lowdensity plasmas in the context of pulsed power systems.  

CP11.00187: Modeling Highly Unsteady Currentdriven Liquid Metal FreeSurface MHD Flows Ramakanth Munipalli, Peter Huang, Rupanshi Chhabra, Alex Mossman, Stephen Howard, Wade Zawalski, Meritt Reynolds, David Plant The flow of electrically conducting liquids in response to a highly unsteady applied current (or magnetic field) is of practical interest in nuclear fusion, and metallurgy. Analytical and seminumerical methods have been used to model such flows for a number of years, but suffer from serious model limitations when there are large and rapid deformations of the free surface, and in complex geometries. We present a candidate timeaccurate simulation method which uses a magnetic vector potential and a scalar electric potential in a general purpose high performance computing software. Variants of this method are often seen in eddy current analysis, but applications in free surface MHD appear limited and rather restrictive. The model permits the flow of current into the conducting elements, and can resolve highly unsteady phenomena and the skin effect. We will present the method with verification, and apply it to the miniSLiC experiment at General Fusion, where a pool of liquid lithium in a steel vessel is rapidly propelled by an electric current pulse (about 1ms) and exhibits interesting dynamics. We will compare numerical results with observed experimental data.  

CP11.00188: Tomographic density profile measurements of spheromak plasma targets for MTF applications Aaron Hossack, Derek A Sutherland, Thomas Jarboe A method of plasma sustainment, imposeddynamo current drive (IDCD), could improve the performance of compact, magnetized plasma targets of interest to ARPAE’s ALPHA fusion portfolio. A new tomography system has been built and installed on the HITSI3 spheromak experiment at the University of Washington. Several hundred chords of light from three poloidal planes and the toroidal mid plane are simultaneously collected by 13 wideangle lenses and imaged onto custom fiber optic bundles. The plasma light travels through a beam splitter after which each leg is filtered to a different He I emission line (668 nm and 728 nm) and collected by a single Phantom v1212 highspeed camera. The plasma density is calculated from the ratio of the lines. This diagnostic is used to assess the effect of imposed electron velocity shear symmetrizing and stabilizing compact, spheromak plasma targets. An improvement in the symmetry of compact plasma targets while preserving gross plasma stability may lead to high energy confinement quality, thereby enabling higher temperature magnetized plasma targets.  

CP11.00189: Fast neutron diagnostics on MTF compression experiments Stephen Howard, Myles Hildebrand, Sandra Barsky Measurement of DD fusion neutrons is a key diagnostic for magnetized target fusion (MTF) experiments being conducted at General Fusion (GF). When combined with other available diagnostics, the detection of DD fusion neutrons can provide strong constraints on a model of plasma evolution during compression, in particular, ion temperature and density. GF plasma compression experiments have been monitored for highenergy particle emission using hydrocarbon liquid scintillator systems of a variety of designs. Scintillator output is digitized at high resolution over the course of the compression shot (2 ms record length). This is followed by offline digital analysis of pulse height and shape of particle detection events. Pulse shape discrimination methods with sufficient accuracy and energy resolution enable separation of neutron detection events from highenergy photon detection events. Inferred DD fusion rates are found to be consistent with other diagnostics and simulations. Scintillator hardware, data analysis and modeling methods will be discussed, as well as experimental results.  

CP11.00190: MHD Stability of a Magnetized Target During NonSelfSimilar Compression Aaron Froese, Dylan P. Brennan General Fusion is designing a magnetized target fusion test reactor that will compress a toroidal plasma inside a liquid metal cavity to heat it to fusion conditions. A magnetized plasma will heat adiabatically if rapidly compressed in a flux conserver (FC) following simple scalings in selfsimilar geometry. In practice, variation of geometry from selfsimilarity complicates the equilibrium and stability calculations that drive the design process. Here we present computations of the plasma stability evaluated for the entire compression of realistic FC geometries. Sequences of equilibria are generated using CORSICA under ideal and adiabatic compression, conserving both the safety factor and entropy profiles. The ideal MHD stability is then computed with DCON. The initial plasma pressure and current density profiles are varied to optimize the stability boundaries. Geometry was found to affect the stability mainly via the q profile. Most cases with q0<1 are found to be n=1 unstable, while those with q0>1 can be susceptible to low n modes. However, viable initial equilibria are found that remain stable throughout the compression.
 

CP11.00191: TimeDependent Helical Magnetic Field Effects on Cylindrical Liner Ablations* Paul C Campbell, Tanner Jones, Cayetano Wagner, Stephanie M Miller, Jeff M Woolstrum, Nicholas Ramey, Akash P Shah, Nicholas M Jordan, YueYing Lau, Ronald Matthew Gilgenbach, Ryan D McBride During cylindrical liner implosions and ablations, magneto RayleighTaylor (MRT) and general magnetohydrodynamic (MHD) instabilities (such as the m=0 “sausage” and the m=1 “kink” instabilities) form. Simulations have indicated that adding a time dependent helical magnetic field using a dynamic screw pinch suppresses MRT instability growth^{1}. We have modeled and fabricated several helical return current structures to generate such a field configuration, with a predicted axial magnetic field of 10 T for peak currents of 550 kA. Simulations of the expected magnetic field profile will be presented, as well as experimental measurements of the magnetic field values achieved, and a comparison of the instabilities observed.
 

CP11.00192: Recent progress in the PI3 spherical tokamak program Kelly Epp, Blake Rablah, Stephen J Howard, Michel Laberge, Meritt Reynolds, Peter O'Shea, William C. Young, Patrick Carle, Aaron Froese, Russ Ivanov Achieving net energy gain with a Magnetized Target Fusion (MTF) system requires the plasma to satisfy a set of performance goals, such as particle inventory (~10^{21} ions), sufficient magnetic flux (~0.3 Wb) to confine the plasma without MHD instability, and initial energy confinement time several times longer than the compression time. To explore the physics of reactorscale plasmas General Fusion (GF) has constructed Plasma Injector 3 (PI3). MTF relies on flux conservation by metal walls and so requires solenoidfree startup with no vertical field coils or toroidal field coils. Therefore the toroidal magnetic field in PI3 is produced by driving current along a single central conductor using a pulsed power supply that also provides a long lowvoltage pulse to compensate resistive losses on multimillisecond timescale. Once the toroidal field is established PI3 uses a short (20us) pulse coaxial helicity injection, from a magnetized Marshall gun, to produce a selforganized spherical tokamak plasma with minor radius 0.65m (the flux conserver radius is 1m). Plasma diagnostics include Mirnov probes, visible imaging, interferometers, optical spectroscopy, Doppler thermometry, Thomson scattering, and FIR polarimetry.  

CP11.00193: Gyrokinetic simulations of influence of electron cyclotron current drive on neoclassical tearing mode in tokamaks Jingchun Li, Zhihong Lin, Kaijie Wang, Chijie Xiao GTC gyrokinetic simulations of the influence of electron cyclotron current drive (ECCD) and ion kinetic effect on the neoclassical tearing mode (NTM) in HL2A configurations have been carried out. The bootstrap current is included with a simple fluid model. We compared the results of the GTC NTM calculations with those of the fluid code, tm8. Effects of ECCD on NTM have also been investigated. It is found that a helicon current drive which is in the same phase as magnetic island opoint is more efficient than a continuous ECCD. Analysis of the GTC simulation reveals that the thermal ion kinetic effects can reduce the island width as well as the growth rate. Finally, the kinetic effects of thermal ions on NTM is found to be more pronounced with higher ion temperature. 
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