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 PP11: Poster Session VI: Relativistic Laser Plasma Interaction and Beam Physics; Boundary; MHD and Stability, Transients; FRC; Dusty Plasmas; Basic Studies; Computational and Diagnostic Methods (2:00pm5:00pm) 
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Room: OCC Exhibit Hall A1&A 

PP11.00001: Development of High Fluence XRay Sources on the NIF Using Laser Heated Novel NanoWire Metal Foams Mark Joseph May, Russ Benjamin, Gregory Kemp, Patrick Poole, Klaus Widmann, Jeff D Colvin, Daniel Thorn, Brent Blue High fluence Kshell xray sources are being developed for high energy density physics experiments. The sources are produced by laser heating free standing pure Ag nano wire foams in the shape of cylinders nominally 4 mm in diameter, 4 mm tall. The manufacture of robust low density foams (6  12 mg/cm3) is now possible through a new technique of freeze drying an aqueous suspension of nanowires. Xray conversion efficiency from these laser heated underdense nanowire foams have been measured to be ∼0.6% which is about twice that observed in more conventional laser heated cavity xray sources. 192 laser beams from NIF are used to heat the foams with ∼400 TW of 3ω laser light in a 2.5 ns square pulse in time depositing ∼950 kJ into each foam. Experimental results and comparisons with simulations will be presented. 

PP11.00002: Laser induced electron bunch generation using Deuterium clusters Prachi Venkat Study of dynamics and energetics of lasercluster interaction has led to various applications, including the production of monoenergetic electron bunches as a result of outer ionization of the cluster. These electron bunches can be further accelerated to higher energies via laser wakefield accelerators. In this work, we propose to study the interaction of intense, subcycle and fewcycles laser pulses with Deuterium clusters for production of monoenergetic electron bunches using 3D, relativistic molecular dynamics simulation. The pulse model used for study of lasercluster interaction has been modified to generate two mutually perpendicularly polarized pulses separated by a finite temporal phase delay. The first pulse is responsible for creating electrons by field ionization of the cluster, while the second pulse tends to accelerate these electrons as a bunch. This electron bunch gets separated from the ionized cluster and can further undergo wakefield acceleration. The complete isolation of the bunch is possible due to the two mutually perpendicularly polarized pulses acting on it. We have also studied the effect of phase delay, pulse duration and peak laser intensity on generation of energetic electron bunches to find the optimum conditions for electron bunch production. 

PP11.00003: Motivation and design of a twocolor interferometer for DARHT AxisII Kimberly A. Schultz, Martin E. Schulze, Michael J. Berninger Unsullied propagation of intense, relativistic electron beams through plasmas is required for multipulse flash radiography. Beamtarget interactions result in a vaporized plume of target material that propagates upstream from the target, affecting the beam focus and quality. Simulations of the plume and its interaction with subsequent pulses is presented here as motivation for the twocolor interferometry (TCI) system being developed for the Dual Axis Radiographic Hydrodynamic Test Facility’s AxisII, a multipulse linear accelerator at Los Alamos National Laboratory. Beam focus positions were calculated with the beaminduced ionization model in LAMDA as a function of plume ionization, density, and volume. Plasma plume evolution, simulated by LASNEX/MCNP calculations, shows plume densities and temperatures consistent with the existence of a partiallyionized plasma. This drives the need for a TCI system, the design and theory of which will be presented. TCI uses interferometers of different wavelengths and can separate the phase contributions of free electrons and neutral particles, which is needed for accurate measurements of partiallyionized plasmas. 

PP11.00004: Kinetic Simulations of MegajouleClass Dense Plasma Focus Devices Ihor Holod, Anthony J. Link, Yuri A Podpaly, Alexander P Povilus, Christopher M Cooper, Steve Chapman, Brian Shaw, Drew P Higginson, Andrea Elizabeth Schmidt, Dale R Welch, David V Rose, Dustin Offermann, Bruce Freeman, Manuel Alan, Michael Butcher Dense Plasma Focus (DPF) is a coaxial plasma gun that concludes its discharge in a Zpinch phase. During the Zpinch, electric field accelerates ions up to several MeV energies. If a deuterium or tritium fill gas is used, the ion beam creates neutrons by fusing during collisions with a dense plasma target as well as the background gas. Due to the low collisionality and significant deviation from the Maxwellian distribution, kinetic simulations are required to describe the pinch phase. We use particleincell code Chicago from the developers of LSP [D. Welch, et.al, Phys. Plasmas 13, 063105 (2006)] to perform simulations of megajouleclass devices. The initial phase of a discharge is simulated using MHD model which is converted to fully kinetic before plasma starts pinching. Results will be presented on model’s agreement of plasma behavior and neutron yield for the Verus Research DPF and for the underconstruction LLNL MJOLNIR DPF. 

PP11.00005: Threshold for ThreeHalvesHarmonic Generation in RelativisticLaserProduced Plasmas Alec Griffith, Matthew R Edwards, Tim Bennett, Julia Mikhailova We present an experimental investigation of threehalvesharmonic generation [1,2] in relativistic laser—plasma interactions at the quartercriticaldensity surface. We analyze the threehalves harmonic energy and spectrum as a function of laser intensity, electron temperature, and plasma gradient scale length, which have been predicted to determine the twoplasmondecay onset [3]. We explore discrepancies between the predicted and observed thresholds for threehalvesharmonic generation. [1] L. Veisz, et al., Physics of Plasmas, vol. 11, no. 6, pp. 3311–3323, (2004) [2] P. K. Singh, et al., Physics of Plasmas, vol. 22, no. 11, p. 113114, (2015) [3] C. S. Liu and M. N. Rosenbluth, The Physics of Fluids, vol. 19, no. 7, pp. 967–971, (1976). 

PP11.00006: Characterization of Femtosecond Laser Filament Conductivity with Varying Pressure James Wymer, Jennifer Elle, Edward Lee Ruden, Alexander Englesbe, Adrian Lucero Our experiments examine the effect of changing gas pressure on the conductivity of an ultra short pulse laser filament plasma and how the conductivity varies longitudinally in the focusing region. By comparing digital images of the plasma fluorescence to its conductivity, we are able to characterize the plasma decay. To determine filament conductivity, we measure microwave scattering along the laser propagation direction. We use a WR284 rectangular waveguide with a 1.5 cm hole that allows the beam through. A 3.2 GHz microwave signal is emitted in the waveguide, and signals are received through a waveguidetocoax antenna connected to a HP8470B Schottky diode. In addition, a series of glass vacuum tubes is used with a 1.2 cm diameter section encompassing the focusing region. This glass tube is passed through the waveguide so measurements can be obtained along the plasma while air pressure is varied from 760 to 0.10 Torr. Filament conductivity is determined by comparing the signal attenuation during filamentation to COMSOL simulations. Our research provides insight into the extent a visual inspection of a filament plasma is representative of its true extent. 

PP11.00007: Verification Of Magnetically Insulated Transmission Lines (MITL) For Power Flow Applications Keith L Cartwright, Peggy J Christenson, Troy C Powell, Timothy D Pointon, Edward G Phillips Timeindependent solutions to electron flows in MITLs have been known for many years. The motivation behind these calculations was to understand experiments by predicting the integrated qualities such as flow current, anode current, cathode current, and voltage. In the process of verifying Finite Element electromagnetic ParticleinCell codes developed at Sandia, EMPHASIS andEMPIRE, it was found that these global quantities were very close to the theoretical results for coarse meshing. This is consistent with earlier codes used for the original designs of HERMES, Saturn, and Z. However, looking at spatial profiles (charge density, current density, velocity, electric and magnetic fields) a finer mesh was required for good comparison to theory. These details matter to the quality of the electron beam for many applications and surface plasma formation 

PP11.00008: Dynamical resonance shift and unification of resonances in shortpulse laser cluster interaction Sagar Sekhar Mahalik, Mrityunjay Kundu Pronounced maximum absorption of laser light irradiating a raregas or metal cluster is widely expected during the linear resonance (LR) when Mieplasma wavelength λ_{M} of electrons equals the laser wavelength λ. On the contrary, by performing molecular dynamics (MD) simulations of an argon cluster irradiated by short 5fs (fwhm) laser pulses it is revealed that, for a given laser pulse energy and a cluster, at each peak intensity there exists a λ  shifted from the expected λ_{M} _{ }that corresponds to a unified dynamical LR at which evolution of the cluster happens through very efficient unification of possible resonances in various stages, including (i) the LR in the initial time of plasma creation, (ii) the LR in the Coulomb expanding phase and (iii) anharmonic resonance in the marginally overdense regime for a relatively longer pulse duration, leading to maximum laser absorption accompanied by maximum outer ionisation and also maximum allowed average charge states. Increasing the laser intensity, the absorption maximum is found to shift in the band of λ ≈ (11.5)λ_{M} than permanently staying at the expected λ_{M}. Present study is important in future generation optimum control experiments where maximum energy is required to transfer from laser fields to charge particles. 

PP11.00009: Transport of the electromagnetic field energy through a plasmalike medium near cutoff Min Sup Hur, Teyoun Kang, Bernhard Ersfeld, Dino Jaroszynski, Kenan Qu, Nathaniel J Fisch The cutoff of propagation of electromagnetic waves in a plasmalike medium is a wellknown phenomenon; when the frequency of the wave is below the cutoff frequency, which is determined by the BohmGross dispersion relation, the wave is reflected leaving behind only an evanescent wave, which does not convey any electromagnetic energy. However, the dispersion relation describing the cutoff applies in a stationary state, whereas near the cutoff condition there is a long transient period before the system reaches a steady state. During this transient period, a significant amount of the field energy is transported through the medium near cutoff. The transient behavior of the field near cutoff has not been illuminated before. In this presentation, we demonstrate, both theoretically and by simulations, that the electromagnetic energy can transport through a plasmalike medium near cutoff over substantial distances. 

PP11.00010: Liquid Lithium Target for Neutron Generation Steven Stemmley, Matthew Szott, Michael P Christenson, Kaitlyn Butler, Brian Jurczyk, David N Ruzic At the University of Illinois, a compact, liquid lithium loop has been developed and tested. The compact, yet scalable, loop is comprised of a stainless steel trench system embedded with heaters and cooling lines, and was designed to handle large heat and particle fluxes in neutron generators as well as fusion devices. Lithium flow is driven through the sole use of TEMHD. The flowing lithium will keep a fresh, clean surface, allowing Li7(d,n) reactions to occur, as well as enhance the deuterium adsorption in the fluid. The enhanced deuterium absorption helps by increasing the total neutron output. Previous work has shown that using a tapered trench design allows for an increase in fluid velocity at the particle strike point. Initial experiments, where a temperature gradient was imposed using the embedded heaters and helium cooling, peak velocities of 16 ± 4 cm/s were observed. For heat fluxes greater than 10 MW/m^{2}, COMSOL fluid models have shown that sufficient velocities (~100’s cm/s) are attainable to prevent significant lithium evaporation. Current work is aimed at determining the necessary velocities and geometry to prevent dryout as well as the system’s neutron output. The early results and discussion will be presented. 

PP11.00011: High repetition rate liquid targets and optics for the study of high intensity laserplasma interactions Kevin M George, John T Morrison, Scott B Feister, John Nees, Joseph R Smith, Adam J Klim, Gregory K. Ngirmang, Joseph C Snyder, Kyle Frische, Chris Orban, Enam A Chowdhury, William M Roquemore Use of high intensity lasers as energetic electron, ion, and photon sources have long served as the primary motivation for the continued study of relativistic laserplasma interactions. However, bringing these applications to bear requires substantial increases in both laser and target repetition rates to achieve necessary fluxes. Here we present liquid targets ideally suited for high repetition rate use based on high velocity liquid microjets. These targets consist of columns or droplets with a diameter of order tens of micron and submicron thick sheets which exhibit the high dimensional and positional stability required for use with commonly employed fast focusing optics. The selfrefreshing nature of the liquid targets enables use at repetition rates exceeding 10 kHz. Efforts to operate in a ‘low vacuum’ environment are detailed with demonstrated operation below 1 mTorr. Additionally, we propose liquid based plasma optics for use with this technique. 

PP11.00012: An Exact Backward Wave Theory for a Thin Tape Helix TravelingWave Tube Abhijit Jassem, Patrick Y Wong, Drew Packard, YueYing Lau The exact smallsignal hottube dispersion relation for a thin tape helix travelingwave tube (TWT) was recently derived [1]. When applied to the forward wave, it gives an exact determination of Pierce’s “AC space charge” parameter Q. In addition, it predicts a significant detune, by as much as 2%, of the cold tube circuit. Here we extend the work to the backward wave mode so as to reexamine Johnson’s classical theory for the threshold of backward wave oscillation in a TWT. [2] [1] P. Wong, D. Chernin, and Y. Y. Lau, “Modification of Pierce’s Classical Theory of TravelingWave Tubes,” IEEE Electron Device Lett. (in press, 2018) [2] H. R. Johnson, Proc. IRE. 43, 684 (1955)


PP11.00013: Electron temperature relaxation and emittance conservation in active plasma lenses Gregory Boyle, JanHendrik Roeckemann, Lucas Schaper, Martin Meisel, Carl A. Lindstrom, Kyrre Sjobak, Erik Adli, Jens Osterhoff Active plasma lenses (APLs) provide strong azimuthallysymmetric focusing fields in an extremely compact size, and may be a key component in future plasmawakefieldbased particle accelerators. However, the effect of an APL on the beam parameters of transiting electron beams must first be evaluated, and potentially mitigated. Within the capillary a nonuniform radial temperature profile develops via Jouleheating and heat loss to the capillary wall [1], resulting in a nonlinear magnetic field profile and contributing to emittance growth. This nonlinearity is most significant at large timescales, i.e., in the quasisteadystate, and is much less significant early in the relaxation process. Here we investigate the relaxation process of the electron temperature in APLs via a magnetohydrodynamic (MHD) simulation. Our results indicate that the differences in emittance growth and radial magnetic field gradients measured in a series of recent experiments [2,3] are primarily due to sampling different parts of the relaxation process. We discuss the implications of our results to the development of emittancepreserving APLs. [1] N. A. Bobrova et al., Phys. Rev. E, 65, 016407 (2001) [2] J.H. Roeckemann et al., submitted to PRAB [3] C. Lindstrøm et al., in preparation.


PP11.00014: Production of relativistic pairs and hard photons in beambeam collisions Thomas Grismayer, Fabrizio Del Gaudio, Ricardo Fonseca, Warren B Mori, Luis O Silva The upgrade of the linear collider at SLAC (FACET II) and the next generation of laser wakefield accelerators (LWFA) will deliver high current ultrashort round bunches capable of reaching the quantum regime at 10s of GeV. We investigate the collision of these beams envisaging a secondary source of collimated gammaray photons and ultrarelativistic pairs. We determine the photon spectrum and the secondary pairs yield both analytically and with PIC simulations with OSIRISQED. Our analytical model and the simulations show excellent agreement. The configuration of the collective fields favors the quantum effects to take place in a localized region resulting in a yield of secondary pairs considerably higher than what previously predicted. Our results demonstrate the potential of this setup as a secondary source of radiation and of relativistic pairs. 

PP11.00015: Numerical comparison of an implicit Vlasov–Maxwell solver with macroparticle methods^{} Alexander Stamm, Bradley Shadwick Assessing the reliability of a macroparticle representation of a kinetic plasma requires understanding its phasespace fidelity as well as conservation properties. While the latter can be expressed analytically, numerical experimentation is required to identify the relative importance of exact conservation as compared with conservation in an average sense for each of the fundamental conservation laws i.e. charge, momentum and energy. Furthermore, the only way to adequately assess the accuracy of the phasespace representation throughout a simulation is by comparison with a demonstrably more accurate method i.e. direct solution of the Vlasov–Maxwell equations. Presently, we take the case of the Weibel instability for our numerical testing. An implicit Vlasov solver in 1½ dimensions (one spatial and two velocity) is compared to a collection of macroparticle algorithms. These include a standard chargeconserving particleincell code, and variational macroparticle codes using either a spatial grid or a Fourier representation, which provides exact momentum conservation. Finally, we investigate the utility of symplectic integrators for the marcoparticle methods. 

PP11.00016: Advanced Fluid Models of BeamWave Interaction in High Power Microwave Sources Peter Stoltz, John W Luginsland, Christine Roark Highpower electromagnetic device modeling require a kinetic treatment, especially for saturation of the device at peak power operation. However, advanced fluid models can capture much of the evolution to the saturated state while requiring less computation time. Fluid models are also especially intriguing considering that many analytic formulations of vacuum electronics devices rely on cold fluid theory. We present results for advanced single fluid and two fluid models of a 5 GHz klystron. We compare electrostatic approximations with full electromagnetic models. We also compare results and computation time with full PIC models. Finally, we validate these models with klystron theory. 

PP11.00017: Fourphoton amplification of powerful laser pulses in plasma Vladimir M Malkin, Nathaniel J Fisch A new scheme for amplification of laser pulses in plasma is proposed, which may overcome limitations of the backward Raman amplification (BRA) scheme. Those limitations are associated primarily with the fragility of the shortwavelength Langmuir waves mediating the resonant energy transfer, which limits the allowed lasertoplasma frequency ratios. The largest frequency ratio allowed decreases with the laser wavelengths and completely disappears at for hard xrays. The BRA limitation on lasertoplasma frequency ratio can be overcome by beating two auxiliary laser pulses, rather than a Langmuir wave, for mediating the energy transfer. This leads to a 4photon amplification scheme, which may be used, for example, to amplify optical laser pulses in very rarefied plasmas, or to amplify xray pulses in dense plasmas. In the 4photon scheme, a pump and an auxiliary laser pulse1 are scattered into an amplified pulse and an auxiliary laser pulse2. The energy can keep flowing from the pump to the amplified pulse even for amplified pulse intensity much exceeding the pump intensity. The opposite process can be excluded by absence of the auxiliary laser pulse2 in freshly encountered plasma layers. 

PP11.00018: Scaling SelfPhase Modulation in fused silica to MIR Wavelengths Matthew Stanfield, Deano Farinella, Nick Beier, Hunter Allison, Sahel Hakimi, Tam Nguyen, Toshiki Tajima, Franklin J Dollar Decreasing pulse durations to the single cycle limit enable new laser interactions, idealized probe beams, and can increase intensity. Selfphase modulation is a nonlinear effect that broadens the spectrum of an intense laser pulse. With sufficient broadening, pulse durations could be compressed to a single cycle pulse duration if the phase is properly controlled. We demonstrate SPM in a variety of targets at wavelengths spanning the near infrared, with measurements of pulse duration, spectral phase, compressibility, and wavefront. Numerical modeling of the nonlinear propagation has also been used to verify nonlinear indices. 

PP11.00019: Attosecondscale absorption at extreme intensities Alex Francis Savin, Aimee Ross, Maris Serzans, Raoul M Trines, Luke Ceurvorst, Naren J Ratan, Ben Spiers, Robert Bingham, Alex Robinson, Peter Andrew Norreys The Zero Vector Potential (ZVP) absorption mechanism, a nonponderomotive absorption mechanism, is expected to dominate the interactions of ultraintense laser pulses with critically overdense plasmas such as those that are expected with the Extreme Light Infrastructure laser systems. We extend the mechanism through the nonponderomotive regime up to QED relevant intensities, showing that at the onset of electronpositron pair production in our numerical simulations the scaling relation of electron energy vs. laser intensity deviates significantly from that predicted by the ZVP model. This offers future experiments the opportunity to test for a distinctive signature in electron energy scalings with laser intensity, thereby providing the opportunity to validate the assumptions of current QED modules in particleincell simulations. 

PP11.00020: MidInfrared Highorder Laser Plasma Interactions in Solids Tam Nguyen, Nick Beier, Jinpu Lin, Hunter Allison, Deano Farinella, Sahel Hakimi, Matthew Stanfield, John Nees, Karl Michael Krushelnick, Franklin J Dollar Relativistic lasersolid interactions are capable of accelerating high energy electron, ion, and xray beams. Most solid highorder harmonic generation experiments to date have been with nearinfrared lasers despite scalings which are strongly wavelength dependent. With the advent of high energy optical parametric amplifiers, relativistically intense short pulse midinfrared experiments are now possible. We report the first results of radiation production from these interactions, with supporting ParticleinCell simulations. 

PP11.00021: Spatiotemporal structure of hard xrays in particleincell codes Miguel Pardal, Jorge M Vieira, Ricardo Fonseca, Antonin SainteMarie The spatiotemporal structure of xrays is important in a range of scenarios, from astrophysics, where it provides unique insights on the origin of energetic radiation in extreme conditions, to microscopy, where it can be important to design light sources to probe new properties of matter. Strong radiation bursts are usually associated with the motion of many individual electrons, where collective plasma effects can be important. The radiation emission from these processes are challenging to model analytically. Thus, numerical approaches are routinely used to describe radiation emission in plasmas. Typical radiation emission diagnostics can capture spectral properties of the emitted light. Instead, in this work, we describe a new radiation diagnostic that captures the spatiotemporal properties of radiation. The algorithm is ideal to describe the radiation from many particles and has been fully integrated with the particleincell code OSIRIS. It has builtin spatial and temporal coherence effects, and can be readily applied to any radiation emission configuration where quantum effects can be neglected. We show that this new tool recovers the theoretical spectra of radiation emission and we use it to compute the spatiotemporal profile of betatron radiation in plasma accelerators. 

PP11.00022: Simulation Study of Ionization and Laser Beam Quality in CO_{2}Laser Plasma Interaction^{} Prabhat Kumar, Roman V. Samulyak, Kwangmin Yu 3D numerical simulations of the interaction of a powerful CO_{2}laser with hydrogen jets demonstrating the role of ionization and laser beam quality on the characteristics of induced wakes are presented. Simulations are performed in support of the plasma wakefield accelerator experiments being conducted at the BNL Accelerator Test Facility (ATF). SPACE, a parallel relativistic ParticleinCell code, developed at SBU and BNL, has been used in these studies. A novelty of the code is its set of efficient atomic physics algorithms that compute ionization and recombination rates on the grid and transfer them to particles. The influence of ionization and laser beam quality on the spectrum of pump laser has been studied for a range of gas densities. Simulations accurately explain the variations in Stokes/antiStokes signal intensities observed in the experiments for different gasreservoir pressures. 

PP11.00023: OSIRIS 4.0: A state of the art framework for kinetic plasma simulations Ricardo Fonseca, Thamine Dalichaouch, Asher Davidson, Fábio Cruz, Fabrizio Del Gaudio, Giannandrea Inchingolo, Anton Helm, Roman Lee, Fei Li, Joshua J May, Kyle Glen Miller, Kevin Schoeffler, Adam R Tableman, Han Wen, Xinlu Xu, Frank ShihYu Tsung, Jorge M Vieira, Marija Vranic, Thomas Grismayer, Viktor K Decyk, Warren B Mori, Luis O Silva The OSIRIS [1] Electromagnetic particleincell (EMPIC) code has been widely used in the numerical modeling of many astrophysical and laboratory scenarios. Since the release of version 4.0, the framework has been continuously developed to support multiple hardware architectures, and to extend the base algorithm, allowing the code to address an increasingly wider range of problems, all from a common code base. In this work we give an overview of the current status of the OSIRIS framework, describing the multiple simulation modes available (Quasi3D, PGC, QED, Shearing and spherical geometries, etc.), and the multiple hardware configurations supported (AVX, KNL, CUDA, etc.). We will also focus on new features being introduced into the code, such as spectral and hybrid field solvers, and alternative charge conservation schemes. Finally, we will discuss some of the software engineering aspects allowing for the development and maintenance of a large code base, and the collaboration of a continuously growing development team.
[1] R. A. Fonseca et al., Lecture Notes in Computer Science 2331, 342351 (2002) 

PP11.00024: Simulation and modelling of diamond emitters in compact sources for high brightness beams Thomas J. T. Kwan, Chengkun Huang, Andrei Piryatinski, Ryan Baker, Heather L Andrews, Dongsung Kim, Ryan Fleming, Kimberley Nichols, Vitaly Pavlenko, Evgenya I SmirnovaSimakov Diamond emitters manufactured from the semiconductor process is a candidate as an electron beam source for advanced compact accelerators and electron microscopy. The micronscale pyramid structure of the emitter allows enhancement of the external field leading to emission with small beam size. We investigate the dependence of field enhancement due to the shape of the emitter and the resulting emission characteristic. The beam dynamics are simulated with the LSP PIC code to characterize the beam size and divergence. To account for electron transport in the bulk material and the tunnelling through the surface, a semiclassical MonteCarlo (MC) emission model is developed for the diamond pyramid. We apply such emission model in our simulations and compare with experiments. The presence of a nanoscale tip from its fabrication process can introduces electronic structure size quantization affecting its transport and tunnelling processes which are accounted for in our nanowire emission model. 

PP11.00025: Development of Unconventional Edge and Scrapeoff Layer Measurements Using Compact Diagnostic Neutral and Ion Beams T P Crowley, D R Demers, P J Fimognari, T D Kile We are developing diagnostic beam techniques to enable equilibrium and fluctuation measurements of density (n_{e}) and magnetic field (B) in edge and scrapeoff layers of magnetically confined plasmas. Simultaneous, localized measurements of these parameters will provide unique insight into edge localized modes, current density, turbulence, and transport. A beam of neutral or singly ionized particles is injected into the plasma and undergoes ionization due to electron impact and charge exchange collisions. Analysis of the resultant charged particles yields information about B and n_{e} at the ionization location within the plasma. The diagnostic is similar to a heavy ion beam probe but has notable differences: the detector is located within the magnetic field of the confinement device, beam energy (and accelerator voltage) requirements are lower, and the system footprint is smaller. We will discuss two areas of innovation: (1) development of a detector and technique that could lead to determination of the magnetic vector potential in the plasma, and (2) simulations of 10100 keV neutral alkali beams that could be used to probe the edge, scrapeoff layer, and regions near the divertor Xpoint of a large tokamak. 

PP11.00026: Effects of 3D magnetic fields on neutral fueling and exhaust at MAST Kurt Flesch, Heinke G Frerichs, James R Harrison, Andrew Kirk, Oliver Schmitz, Ian Waters The application of resonant magnetic perturbations (RMPs) at MAST has been shown to cause density pumpout during discharges that have a particular MHD response. This occurs in both Lmode and Hmode discharges. An analysis of the changes in fueling and exhaust show that RMPs cause an increase in total fueling to the plasma, from D_{α} emission measurements, but also a significant drop in particle confinement time, from a 0D single reservoir particle balance of the main ion species, such that there is a net particle pumpout. In order to better understand the impact of neutrals to this pumpout, a 1D global particle balance with reservoirs for both atomic and molecular deuterium is used. This simple model can accurately reproduce experimental conditions and can also be used to explore the parameters describing the plasmasurface interactions and fueling fraction of ionized particles to the core and how those terms change with the RMP application. New Wisconsin InSitu Penning (WISP) gauges are being installed on MASTU to aid in measurement of neutral pressure in the vessel and divertor regions for future particle balance analysis with the capability to measure helium and other impurity concentrations. 

PP11.00027: Performance simulation of divertor neutral baffles in the TCV tokamak with the SolEdge2DEIRENE code Davide Galassi, Christian Theiler, Holger Reimerdes, Hugo Bufferand, Guido Ciraolo, Patrick Tamain, Marcelo Baquero, Hugo De Oliveira, Basil Duval, Olivier Février, Eva Havlickova, Paolo Innocente, Yannick Marandet, Roberto Maurizio, Cedric Tsui, Kevin Verhaegh, Mirko Wensing A gas baffle will soon be inserted in the vessel of the tokamak à configuration variable (TCV) [Reimerdes, Nucl. Mat. and Energy 2017]. This upgrade aims at achieving more favorable conditions for the onset of detachment. In this work, we simulate the effect of the baffle on the TCV edge plasma with the SolEdge2DEIRENE code [Bufferand, Nucl. Fusion 2015], which couples a fluid plasma model to a kinetic model for neutrals and impurities. Firstly, a specific TCV shot with a bafflecompatible shape is simulated. This comparison allows to tune perpendicular transport coefficients in order to match upstream experimental profiles, and results in a good agreement with the experiment at the targets. The same simulation is then carried out including the baffle. The neutral compression ratio, namely the ratio between divertor and upstream neutral pressure, is shown to improve by a factor of order 10, resulting in bigger power and momentum losses in the divertor plasma. Next, we perform a scan in upstream density to access different divertor regimes, revealing that the neutral compression increases as we approach detachment. Finally, in view of possible future optimizations, the level of baffle closure is varied in the simulations and the feedback on plasma properties is discussed. 

PP11.00028: Reconstruction of visible emission in ASDEX Upgrade divertor Matteo Agostini, Nicola Vianello, Daniel Carralero, Lorella Carraro, Marco Cavedon, Ralph Dux, Tilmann Lunt, Volker Naulin, Monica Spolaore, Elisabeth Wolfrum, the ASDEX Upgrade Team, the EUROfusion MST1 Team A tomographic algorithm for obtaining the 2D emission of D_{α} and D_{γ} in the divertor region of ASDEX Upgrade is developed. It allows for characterizing the time and space evolution of the D emission in the visible range, in particular when the electron density increases during the discharge. At higher Greenwald fraction, the density profile in the scrapeoff layer (SOL) becomes flatter, with the formation of a shoulder. With this phenomenon, a change in the SOL transport is observed, with a modification in the behavior of turbulent blobs, which become larger. At the same time, the tomography shows that visible emission, which is localized in the inner divertor target at lower n_{e}, extends in the whole divertor region when density increases, and this effect can be due to a change in n_{e}, T_{e} and neutral profile density. From the measurements of D_{α} and D_{γ} emission it is possible to estimate these quantities, and thus studying the role of the divertor neutrals on the shoulder formation. In fact they could lead to density shoulder formation by reducing the flow of ions parallel to the field and by changing the radial electric field affecting SOL turbulence and blobs characteristics [1]. [1] A.Wynn et al., 2018 Nucl. Fusion 58 056001 

PP11.00029: Coupled modeling of dust and plasma dynamics in tokamaks with DUSTTUEDGE code Roman Smirnov, Sergei Krasheninnikov Dust events are commonly observed in present tokamaks and are expected to substantially contribute to impurity contamination of plasmas in future fusion devices. Dust formation and mobilization in tokamaks are often associated with transient plasma phenomena, leading to intermittent ejection of large amounts of dust into the plasmas. To study the impact of the intermittent dust events on fusion plasmas, we developed coupled DUSTTUEDGE code package simulating selfconsistent dynamics of dust and plasma in tokamaks. Due to very large perturbations introduced by dust injection into plasma the selfconsistent modeling presents significant challenges. We report on progress in the development of the coupled modeling capabilities and present latest results on simulations of the impact of transient ejection of large tungsten dust grains on fusion edge plasmas. In particular, improvements in the code convergence were achieved, which allowed to simulate detachment dynamics during tungsten dust ejection events in ITERlike divertor plasmas. 

PP11.00030: Pedestal fueling variation in a closed divertor configuration at DIIID Andrew Oak Nelson, Egemen Kolemen, Florian Laggner, Olivier Izacard, Richard Joseph Groebner, David Eldon, Morgan W Shafer, Anthony W Leonard, Daisuke Shiraki, Aaron C Sontag The role of particle fueling on the pedestal was examined in a closed divertor geometry at DIIID. By varying fueling schemes between gas puff and pellet injection, the particle source location was increased in the core relative to the edge. Discharges with particle injection rates from 5 to 40 Torr L s^{1} in combination with either neutral beam heating (which contributes to central fueling) or electron cyclotron heating (no fueling) were compared. The different fueling schemes, which are expected to vary the particle source profile, were shown to impact the density pedestal structure, which in turn affects stability and plasma performance. Equilibria and profiles are generated using CAKE (an automatic kinetic equilibria generating tool), and transport properties and heating schemes are investigated with TRANSP. Pellet injection is shown to significantly increase the pedestal top density and flatten the maximum electron temperature gradient, whereas increased gas puff shifts the density profile radially outwards. 

PP11.00031: Hydronitrogenenhanced MAR process in D_{2}N_{2} plasmas to induce plasma detachment SHOTA ABE, Saikat Chakraborty Thakur, Russ Doerner, George R Tynan The Molecular Assisted Recombination (MAR) process is thought to be a main channel of volumetric recombination to induce the plasma detachment operation. Authors have suggested a new plasma recombination process supported by hydronitrogen molecules such as ammonia, which will be formed by impurity seeding of N2 for controlling divertor plasma temperature and heat loads in ITER. This hydronitrogenenhanced MAR (HNMAR) process would occur throughout two steps: 1) ion exchange reactions between hydrogen ions and ammonia molecules, 2) recombination reactions between NH3/4+ ions and electrons. In this study, the HNMAR process is investigated in plasmas ne ~ 10161018 m3 fueled by D2 and ND3 in the PISCESE RF plasma device. Ion densities are calculated and directly measured by using a rate equation model and a calibrated Electrostatic Quadrupole Plasma (EQP). The EQP detected ND3/4+ ions (1075% of whole ion densities) which is the production of the step 1 reaction according to the model estimation. When ne > 1017 m3, the volumetric recombination process (step 2) cannot be ignored by comparing with the surface loss reaction. In the plasmas ne~ 10171018 m3, the experimental result shows good agreement with the model including the step 2 recombination reactions. 

PP11.00032: First time observation of local current shrinkage during the MARFE behavior on the JTEXT tokamak Peng Shi, Ge Zhuang Multifaceted asymmetric radiation as well as strong poloidal asymmetry of the electron density from the edge, dubbed as ‘MARFE’, has been observed in high electron density Ohmically heated plasmas on JTEXT tokamak. Equilibrium reconstruction based on the measured data from the 17channel FIR polarimeter–interferometer indicates that an asymmetric plasma current density distribution forms at the edge region and the plasma current shrinkage locate at the MARFE affected region. Furthermore, associated with the localized plasma current shrinkage, a locked mode MHD activity is excited, which then terminate the discharge with a major disruption. Localized plasma current shrinkage at the MARFE region is considered to be the direct cause for the density limit disruptions, and the proposed interpretation is consistent with the experimental observations. 

PP11.00033: Xdivertor study with SOLPSITER Zhongping Chen, Michael T. Kotschenreuther, Swadesh Mitter Mahajan We will study the Xdivertor (XD) geometry, in comparison to the standard divertgor (SD), in JET and MASTUpgrade using the latest SOLPSITER simulation code. According to our previous experience with DIIID and NSTXU we expect the XD to mitigate the exhaust power better than the SD in JET and MASTU as well. We hope to show that the scrapeofflayer can detach at a lower upstream density in the XD cases, and can keep a localized detachment front near the target, away from the core plasma. We will examine the the physical mechanisms of the flaring effect in details. 

PP11.00034: Scrapeoff layer turbulence and transport in the wide divertor heatflux width simulations of ITER Randy M Churchill, CS Seock Chang, Seung Hoe Ku, Robert Hager Recent simulations [1] with the gyrokinetic turbulence code XGC1 have predicted that the midplaneprojected heatflux width on fullfield ITER will be much wider (~6mm) than the expected value from a multimachine experimental scaling (<1mm) [2]. This result would greatly open the operational space of ITER, and as such a more fundamental understanding is warranted in to why the simulation departs from the experimental scaling. Heuristic scaling arguments suggest that the main reason for the difference is that in the fullfield ITER the nonlinear edge turbulence plays a more dominant role in setting the heatflux width. This work will present a more detailed look at the turbulence characteristics of this ITER simulation in comparison with simulations on lowfield ITER and devices such as CMod, to begin to understand the mechanisms at play. Beyond typical turbulence characteristics, a focus will be given to the turbulence along the entire scrapeoff layer, including through the divertor region.
[1] C.S. Chang, et. al., Nucl. Fusion 57 (2017) 116023. [2] T. Eich, et. al., Nucl. Fusion 53 (2013) 093031. 

PP11.00035: Implementation and testing of a 3D extension of the SOLT model for tokamak edge turbulence* M. V. Umansky, J. R. Myra, D. A. Russell, A. M. Dimits Progress is reported on development of a 3D extension of the tokamak edge turbulence model SOLT [1]. The original SOLT solves for timeevolution of plasma density, temperature, and electrostatic potential in 2D, in a plane perpendicular to the magnetic field in the outboard midplane region of a tokamak; dynamics along the magnetic field is approximated by a parallel scale length parameter. The extended 3D version of SOLT, being developed in the BOUT++ framework [2], follows the original SOLT physics model but includes parallel variations of plasma fields and electron dynamics along the magnetic field line. Like the original SOLT, it models a domain representing the outer midplane region of a tokamak around the last closed flux surface, and divertor target plates are represented by sheath boundary conditions. Testing of the model includes verification of linear instabilities supported by the model, driftresistiveballooning and conductingwall modes, and nonlinear solutions for isolated plasma filament propagation in the SOL. [1] Russell et al., Phys. Plasmas 22, 092311 (2015); [2] Dudson et al., Comp. Phys. Comm. 180, 1467–1480 (2009). 

PP11.00036: Development of a test facility for divertor cooling techniques and plasma diagnostics KilByoung Chai, DuckHee Kwon, Min Park Divertor has been adopted in the current magnetically confined fusion to remove helium ashes produced by DT fusion reactions from the reactor. The divertor plate in ITER is expected to encounter 1020 MW/m^{2 }heat flux and 10^{24} /m^{2}/s particle flux; both are several times higher than current fusion devices. Thus, it is necessary to develop efficient divertor cooling techniques which can handle such heat and particle fluxes. In this purpose, we have been constructing a test facility producing the heat and particle fluxes of divertor regions and we will use it to study divertor cooling techniques and to develop divertor plasma diagnostics. The plasma source based on the appliedfield magnetoplasmadynamic thruster concept was built and the first plasma was successfully obtained with a 1 kW ignition power supply. In order to provide high heat and particle fluxes as divertor regions, a 100 kW dc power supply will be used in the future. For applying external magnetic field, an NdFeB magnet which can provide B_{z }= 0.15 T on the axial axis is used. To measure the plasma parameters, Langmuir probe array similar to the KSTAR divertor probe array will be used. The detailed performance and measured plasma parameters will be discussed in a paper. 

PP11.00037: Reduced domain studies of divertorlocalized modes in spherical tokamaks Derek Baver, James Myra, Filippo Scotti, Stewart J Zweben, Fulvio Militello Instabilities in the divertor legs of spherical tokamaks are of interest for a number of reasons, such as determining the width of the plasma at the divertor plate. However, such instabilities are challenging to model due to high levels of magnetic shear in this region. This in turn results in instabilities with fine structures requiring high resolution to model accurately. One solution to this problem is to construct grids localized to the region of interest. By modeling such domains using the ArbiTER eigenvalue code, we can determine the structure and mechanism of these instabilities. 

PP11.00038: Predictions of ICRF induced sheaths and sputtering in the LAPD experiment John Christopher Wright, Syunichi Shiraiwa, Davide Curreli, Moutaz Elias, Cornwall Hong Man Lau, James Richard Myra, Bart G.P. Van Compernolle, Rory James Perkins A major goal of ICRF research is to design an antenna that minimizes impurity production while coupling substantial power to the plasma. The LArge Plasma Device (LAPD) at UCLA provides a flexible and accessible platform for validation studies of ICRF wave core propagation and interaction with plasma facing components. LAPD has a 100 kW single strap ICRF antenna and has plasmas with densities of and temperatures of that is similar to the edge of a tokamak or stellerator. We apply the PetraM RF module to ICRF scenarios in LAPD including fast and slow wave propagation. We will show validation studies on wave propagation measurements and discuss model results for slow wave mode conversion to the ion plasma wave and fast wave incident on a conducting plate. The conducting plate study will also include calculations of RF sheath potentials and estimates of sputtering yields for different plate materials under a helium plasma. 

PP11.00039: A Landau Fluid Closure for Arbitrary Frequency and Its Implementation in Numerical Code Libo Wang, Xueqiao Xu The perturbed heat flux and temperature for Landau damping case are calculated directly. The relationship between these two physical quantities is the same as HammettPerkins’ closure in low frequency limit. Another method to get Landau fluid (LF) closure, such as ChapmanEnskoglike (CEL) method, is analyzed. It shows that the CEL method produces the same closure as that of kinetic method only when background distribution is Maxwellian. To bridge the low and high frequency limit, the harmonic average form of kinetic LF closure is developed which shows that the transport is nonlocal both on space and time. The harmonic average closure depends on wave frequency and yields a better agreement with kinetic response function than that of HammettPerkins’ closure. The implementation in numerical code is also presented, based on an approximation by a sum of diffusionconvection solves (SDCS). The three moment Landaufluid model has been implemented in the BOUT++ code using the SDCS method for the harmonic average form of LF closure. Good agreement has been obtained for the response function between driven initialvalue calculations using this implementation and matrix eigenvalue calculations using SDCS implementation of the LF closure. 

PP11.00040: TITLE: Numerical Studies of Sheath at Tokamak Edge Yuzhi Li, Bhuvana Srinivasan, Xianzhu Tang, Zehua Guo Plasmasurface interaction has been considered to be of great importance during a tokamak disruption event. Plasma particles interact with solid surface within the sheath layer which has a strong influence on the particle and energy flux towards the wall. In classical sheath model, many assumptions are made in order to obtain a simplified analytical model. However, at the tokamak edge, where sharp temperature gradient, strong inelastic collisions, and high recycling regime exists, some of the assumptions may not be valid. Thus, a kinetic study of divertor sheath will be helpful for understanding the physics. In present work, we develop a Monte Carlo Collision (MCC) package for vector particle in cell (VPIC) code, where elastic and inelastic interactions between charged particles and neutrals are included. Simulation results of plasma distribution profile and sheath parameters will be presented. 

PP11.00041: A numerical study of plasmaneutral interaction in a coaxial electrode configuration Sina Taheri, Uri Shumlak, Jacob R King The flow Zpinch concept magnetically confines a hightemperature, highdensity plasma, while using sheared axial flows to provide stability. The Zpinch has a simple, linear configuration in which the selffield generated by the axial current compresses plasma up to 1000 eV and confines it for 2060 microseconds. Interactions between plasma and neutral species can have a large effect on the dynamic behavior both during plasma acceleration and when the Zpinch plasma is magnetically confined. In this research, a reacting plasmaneutral model [Meier \& Shumlak, POP 19 (2012)] is incorporated into the NIMROD plasma simulation code to explore the effects of neutral gas in the acceleration phase of a zpinch device. This combines a magnetohydrodynamic (MHD) plasma model with a gas dynamic neutral fluid model allowing for the study of electronimpact ionization, radiative recombination, and resonant chargeexchange in plasmaneutral systems. The acceleration section of the flow Zpinch is modeled as a coaxial electrode accelerator, and neutral gas effects on current sheet propagation and spreading are investigated. Simulations with experimentally relevant current injection lead to current sheet propagation at about 40 km/s. 

PP11.00042: Kinetic Physics in Tokamak Boundary Plasma J. Dominski, CS Chang, Seung Hoe Ku, and the XGC team Unlike the core plasma, tokamak boundary plasma is in a nonequilibrium or a farfromequilibrium thermodynamic state. Individual particle orbits can significantly deviate from the usual equilibrium statistical behaviors, transport may not obey Fick’s law, the transport timescale may not be diffusive, plasma can easily become nonMaxwellian, the conventional fluid closures based on the nearequilibrium thermodynamics –including the wellutilized CGL closure and Braginskii viscosity – may not be valid, and plasma turbulence may not be of usual type seen in the core plasma. A kinetic simulation may be needed for higher fidelity understanding of the boundary physics and for improvement of fluid closures. This talk will introduce the kinetic aspect of the boundary plasma that may not be easily captured by fluid moments equations and that may help improve fluid simulations through collaborative effort. The spatial region of discussion will include the Hmode pedestal, the magnetic separatrix and the Xpoint, and the scrapeoff region that is in contact with the material wall. Neutral particle kinetics will also be discussed. Update on LH transition dynamics, and SOL and divertor heatload physics will be discussed as examples. 

PP11.00043: Realtime modelbased wall heat flux estimation for ITER Himank Anand, Richard A Pitts, Peter C de Vries, Joseph A Snipes, Isabel Nunes, Luca Zabeo, Cristian Galperti, Federico Nespoli, Roberto Maurizio, Stefano Coda, Benoit Labit, Holger Reimerdes A realtime (RT) first wall (FW) heat load control system will be required at a very early stage of ITER plasma operations. A Matlab/Simulink architecture containing a 2D, control oriented model, based on RT equilibrium reconstruction has been successfully implemented for the ITER Plasma Control System (PCS). Integration of the real 3D nature of the ITER PFCs into the algorithm is performed by offline determination of the heat load distribution on a full 3D poloidal sector using a new magnetic field line tracing utility, SMITER, permitting import and appropriate meshing of CAD descriptions of the FW geometry. Weighting factors are then derived with which to correct the peak heat fluxes obtained from the 2D model for implementation into the heat flux control algorithm. A detailed study of the rampup phase in a limiter configuration has been performed using the DINA code to generate magnetic equilibria and including a plasma current scaled, double exponential radial profile of parallel heat flux. The approach proposed for ITER has been experimentally demonstrated and benchmarked against offline measurements from infrared (IR) camera diagnostics for both limiter and diverted plasma configurations on the TCV tokamak. 

PP11.00044: Improvements Prepared for the ECCD Stabilization of m/n=2/1 NTMs in the DIIID LowTorque ITER Baseline Scenario Robert La Haye, David Humphreys, John Lohr, Erik Olofsson, Edward Strait, Anders Welander, Egemen Kolemen Experiments in DIIID are continuing to study how to minimize the average Electron Cyclotron Current Drive power directed at q=2 for stabilization of the m/n=2/1 Neoclassical Tearing Mode in the ITER baseline scenario. Standby “lieinwait” ECCD to “catch” a growing mode, turn on the ECCD, “subdue” the mode with return to standby EC off is under development. ITER will need to keep the average EC power for stabilization minimal to maximize Q. The lowtorque makes early mode detection imperative for prompt subduing before walllocking. Previous DIIID experiments identified problems: 1) gyrotrons could not fully be off in standby and only for a limited time and 2) the n=1 N1RMS for the catch had to be set too high to avoid false positives. Improvements to gyrotron modulation now allow fullyoff without limit on offtime; ODDEVENSPEC is now deployed to distinguish n=1 m=2 from n=1 m=1 so as to lower the bar for catching the mode onset. More gyrotons and EC power will facilitate promptly subduing the mode. 

PP11.00045: Riccati method for numerical tearing layers Andrew Cole, John M Finn, Cihan Akcay, Dylan P. Brennan We present a method for numerical solution of the tearing mode dispersion relation based on a technique for integrating stiff equations due to Forman Acton. The method is robustly stable for the tearing layers studied, and should be broadly applicable. The tearing layer equations are first Fourier transformed (FT), followed by a change of dependent variable using the Riccatilike transform w=kφ'(k)/φ(k) where φ(k) is the FT stream function. The solution is obtained via backwards integration from large k to zero. The Riccati transformation separates the `good' and `bad' solutions (as k>∞) in the range of the Riccati variable w. The tearing layer dispersion function is related to the slope of the Riccati variable at k=0, and found by least squares fitting to a Pade approximant there. 

PP11.00046: Mechanism for toroidal localization of edge ballooning instability in the presence of strong applied 3D magnetic perturbations Tyler Cote, Matthias Willensdorfer, Erika Strumberger, Chris C Hegna, Hartmut Zohm, Wolfgang Suttrop Recent observations on ASDEXUpgrade have shown toroidally localized MHD activity in the presence of strong applied 3D magnetic perturbations [1]. In this work, we utilize VMEC to construct 3D MHD equilibria associated with ASDEXUpgrade Hmode discharges with applied 3D magnetic perturbations. Subsequent analysis of the infiniten ballooning stability of these equilibrium demonstrates strong agreement between theory and the experiment, with the ballooning instability having strong toroidal localization and dependence on the magnitude of the 3D edge displacement. Analysis shows localization of the ballooning mode to specific fieldlines corresponding to locations in the pedestal region where there is a minima in the integrated local magnetic shear. This reduces the stabilizing fieldline bending energy, causing the onset of the ballooning instability. 3D distortion of the flux surfaces cause significant change in the normal torsion, a key component of the local shear, and acts as the primary mechanism for ballooning destabilization on certain fieldlines. [1] M. Willlensdorfer et al., Physics Review Letters, 119 (2017). 

PP11.00047: Core magnetic shear effects on energetic ion drive to disruptive instabilities Dylan Brennan, Andrew J Cole, Charlson ChiSun Kim, Cihan Akcay, John M Finn Simulations of the onset of resistive MHD instabilities are presented where a slowing down distribution of energetic ions can either stabilize or destabilize disruptive tearing modes depending on the magnetic shear in the core. Two cases are compared, one with monotonic shear throughout the profile and one with reversed shear in the core. The monotonic case has a minimum q of 1.1 while the reversed case has a minimum of 1.3. Outside of the reversal the profiles and equilibrium structure are nearly identical between the two cases. The drive from energetic ions is stabilizing in monotonic shear and destabilizing in reversed shear, consistent with previous work. In the reversed shear case without energetic ions a 3/2 mode is unstable, while with ions both a 2/1 and 3/2 mode are driven. The beta limits as a function of rotation with a resistive wall are modified by the energetic ions in a reduced model depending on the magnetic shear. Nonlinear simulations with energetic ions are also explored, and analyzed in terms of the linear results and a reduced model of the energetic ion effect on the resistive mode. 

PP11.00048: Locking to an error field in the presence of real tearing frequencies due to finite β Cihan Akcay, John M Finn, Dylan P. Brennan, Andrew J Cole We present NIMROD simulations to study error field locking behavior in plasmas having marginally stable tearing modes with real frequencies. Real frequency modes are caused by pressure gradient, curvature, and parallel dynamics in the resistiveinertial (RI) and viscoresistive (VR) tearing regimes. A periodic cylinder with a hollow pressure profile is used to model the toroidal effects. In the linear regime, raising β stabilizes the 2/1 tearing mode and leads to real frequencies. Stabilization is due to both the positive pressure gradient in the outer region and favorable curvature in the tearing layer. Linear simulations with rotation and an error field of magnitude ε show that the maximum reconnected flux occurs at the tearing mode phase velocity. In the nonlinear simulations, the plasma flow at the rational surface locks to a rotation just above the tearing mode phase velocity. Increasing ε further results in a large island that flattens the pressure, causing further nonlinear growth and terminating the propagation of the real frequency of the tearing mode. We describe the interplay of three nonlinear effects: current flattening, pressure flattening, and locking. 

PP11.00049: Bornlocked neoclassical tearing mode triggered by error field penetration Seiya Nishimura, Ryusuke Numata We investigate magnetic islands in the coexisting system of the error field and the perturbed bootstrap current. In numerical simulations, it is observed that the bornlocked neoclassical tearing mode, which is locked at its onset, is triggered by the penetration of the error field. The necessary vacuum island width to directly trigger the locked neoclassical tearing mode is found to be smaller than the seed island width to trigger the original neoclassical tearing mode. This implies that the error field penetration is an efficient trigger mechanism of the neoclassical tearing mode. The error field penetration threshold is weakly affected by the perturbed bootstrap current. This implies that, the conventional theory about the penetration threshold in the lowbeta regime may be applicable to the highbeta regime, where the neoclassical tearing mode threshold is approached. However, once the error field penetration occurs, the perturbed bootstrap current enhances the saturated magnetic island width which overwhelms the vacuum island width. This enhancement is directly linked to the excitation of the bornlocked neoclassical tearing mode. 

PP11.00050: Suppression of Tearing Modes by RF Current Condensation A. H. Reiman, N. J. Fisch Currents driven by rf (radio frequency) waves in the interior of magnetic islands can be used to stabilize deleterious tearing modes in tokamaks. Present analyses of stabilization strategies assume that the local deposition of rf power and the local rf acceleration of electrons are unaffected by the presence of an island, implying that the current required to stabilize the island increases as its width increases. It is shown here, however, that there is a threshold island width above which this assumption is significantly violated. There is a current condensation in the island, with a threshold width above which there is a decrease in the required current, and a second threshold at which the condensation effect is dramatically enhanced, allowing the stabilization of larger islands with more efficient use of the driven current. There is a hysteresis effect above the second threshold that shrinks the island to smaller width. The condensation effect also reduces the difficulty of aiming the rf current deposition for accurate radial alignment with the center of the island by concentrating the current deposition near the island center. 

PP11.00051: Radiationdriven islands of the resistive tearing mode in Tokamaks Haiwen Xu, Yuanhong Song, Zhiwei Ma, Younian Wang We investigate the influence of the bremsstrahlung radiation on the evolution and saturation of the m/n=2/1 resistive tearing mode (m and n are, respectively, the poloidal and toroidal Fourier mode numbers), by using a 3D toroidal MHD code (CLT). Being the power balance between the Ohmic heating and the radiative cooling inside the magnetic island, the stability criterion for radiation driven islands has been taken into account. It is found that if impurities (such as carbon, iron and tungsten, etc.) exist in the magnetic island, strong destabilization of the tearing mode will be made due to an imbalance of local radiative cooling and Ohmic heating inside the island. As a result, the width of the magnetic island will increase significantly, even larger than twenty percent of the minor radius. Moreover, the radiation reduces the pressure inside the magnetic island and further shrinks the current profile inside the island. The modified Rutherford equation (MRE), which contains radiation and current asymmetric effects, can reasonably explain the above physical mechanism of radiationdriven magnetic island growth. 

PP11.00052: Suppressing Locked Magnetic Island with Wavedriven Currents Ben Israeli, Allan Reiman The use of localized electron cylcotron current drive has been studied extensively as a means to control and mitigate magnetic islands in tokamaks. The use of static field perturbations to align locked neoclassical tearing modes with wavedriven currents has been demonstrated in DIIID (F.A. Volpe et al., Phys. Rev. Letters 115, 175002, 2015), and sensitivity of tearing mode suppression to wave injection alignment has been shown numerically (D. De Lazzari, E. Westerhof, Nucl. Fusion 49, 075002, 2009). We introduce a static perturbation to a cylindrical or axisymmetric toroidal field, and investigate the effect of wave injection alignment and width on the suppression of a resonant magnetic island using a simple numerical model. We consider the impact of these parameters on the effectiveness of wavedriven currents in stabilizing the growth of locked modes. Predictions are given in parameter ranges relevant to DIIID and ITER. 

PP11.00053: Investigation of the coupling between energetic electrons and the m/n=1/1 mode in the TCV tokamak Dahye Choi, Antoine Merle, Stefano Coda, Joan Decker, Jonathan P Graves During ECRH/ECCD experiments on the TCV tokamak, a frequencychirping mode with poloidal and toroidal mode numbers m=1 and n=1 is observed. Magnetic probe analysis, aided by toroidal rotation measurements with charge exchange spectroscopy, shows that the fishbonelike mode is rotating in the electron diamagnetic drift direction. The redistribution of thermal and suprathermal electrons by the mode is measured using the soft Xray and the hard Xray tomographic spectrometer systems. The interaction between energetic electrons and the mode is investigated by solving the dispersion relation of the fishbone mode, using the MIKE code coupled to the relativistic FokkerPlanck code LUKE. 

PP11.00054: A Riccati Implementation of Ideal MHD Stability Analysis Alexander Glasser, Egemen Kolemen, A. H. Glasser It has recently been shown that the quadratic Hamiltonian associated to the energy of ideal MHD perturbations makes the δW analysis of plasma stability into a standard Riccati problem of optimal control theory. In particular, it has been shown that the Newcomb equation for extremal plasma perturbations can be reduced to a Riccati matrix differential equation. This equivalent Riccati formulation directly solves for the stability characteristics of a plasma equilibriumthat is, the plasma response matrixand enjoys a number of numerical advantages over the Hamiltonian solution approach. In this work, we implement and demonstrate the efficacy of this Riccati formulation, revealing it to be a viable alternative calculation method for ideal MHD stability analysis. We discuss some of the applications that such an alternative formulation affords. 

PP11.00055: NIMROD Simulations of Forced Magnetic Reconnection in DIIID Limited Lmode Plasmas Matthew Beidler, James D Callen, Todd E Evans, Chris C Hegna, Morgan Shafer, Carl Sovinec This work focuses on physics of mode penetration in limited, Lmode plasmas in the DIIID tokamak using the extendedmagnetohydrodynamic code NIMROD. Simulations are initialized with results from kineticEFIT for magnetic profiles, OMFIT for thermal and rotation profiles, and TRIP3D for vacuum magnetic perturbation fields. When the resonant magnetic perturbation (RMP) magnitude is increased in a rotating plasma, the electromagnetic force imparted by the RMP on the flowscreened island can decrease the local flow, causing the external field to rapidly penetrate. Furthermore, the plasma response at a rational surface depends on dissipation and rotation, setting the threshold RMP for mode penetration. To elucidate the plasma response due to applied RMPs, we present parametric analyses of linear simulations scaling rotation and dissipation. Numerical results are compared to conventional analytical treatments including tearing and twisting plasma responses. Intuition gained from linear results will be utilized in a nonlinear study of mode penetration with tentative comparisons to DIIID results. 

PP11.00056: Progress on Modeling Asymmetric Vertical Displacement Events with NIMROD C. R. Sovinec, K. J. Bunkers Recent nonlinear fluidbased computations of asymmetric vertical displacement events (AVDEs) evolve equilibriumscale fields selfconsistently with MHD perturbations, including rudimentary anisotropic transport evaluated in the timedependent 3D fields. Implicit computation with the NIMROD code [Sovinec, et al., JCP 195, 355 (2004)] allows large separation of the Alfvenic, resistivewall, and plasmaresistive temporal scales, which is representative of most large experiments. Results show distinct thermal quench (TQ) and current quench (CQ) phases with the characteristic increase of net plasma current occurring when the current density profile broadens due to the MHD activity that induces the TQ. Asymmetric magnetic fields that penetrate the resistive wall lead to horizontal forcing. NIMROD AVDE computations use the thinshell model, where the surface current density that leads to force density is tantamount to the discontinuity in tangential field across the wall. Here, it is natural to use the Pustovitov computation of integrated magnetic stress over the outer surface of the shell [NF 55, 113032 (2015)], which assumes that the plasmawall system is electrically isolated and that plasma inertia is negligible. 

PP11.00057: Magnetic Presheath Boundary Conditions for NIMROD VDE Computations* Kyle J Bunkers, C. R. Sovinec In general, VDE computations are expected to be sensitive to their boundary conditions. Axisymmetric resistiveMHD computations with the NIMROD code have shown that the computed halo current distribution depends on the temperature boundary condition and on the particle density boundary condition [Bunkers and Sovinec, BAPS 62, No. 12 (2017)]. Actual plasma contact with material surfaces leads to sheath effects that are impractical to resolve in global simulations. A practical alternative is a set of boundary conditions that represents conditions at the magnetic presheath entrance, which has been developed for plasma turbulence simulations [Loizu, et al., Phys. Plasmas 19, 122307]. Implementing these presheathentrance conditions in NIMROD requires adapting the model for the nonreduced system of equations. The axisymmetric VDE calculations presented here compare the influence of various boundary conditions. Application of the lowestorder magnetic presheath effects produces significantly different behavior relative to the standard, mathematically simpler boundary conditions. In particular, the flow smoothly connects to the wall when the magnetic presheath boundary conditions are applied. 

PP11.00058: Simulation of Resistive Wall Modes using NIMROD Ge Wang, Carl R Sovinec The resistive wall mode (RWM) is an external, or free boundary, MHD kink instability in the presence of a wall with finite conductivity. It leads to beta limits and is also considered as one of the significant reasons for the triggering of disruptions in the tokamak. In this study, RWMs are modeled with the highorder spectral finite element code NIMROD, which has been verified with the analytic linear theory for RWM in cylindrical geometry for a range of wall positions and wall resistivities. New linear results for toroidal geometry compare two different numerical approaches for the resistive wall, a Green’s function approach and a Lagrange multiplier approach with a meshed external vacuum region. The code is used to study the nonlinear evolution of a RWM in a tokamak with a large aspect ratio and nearly circular crosssection, where the most unstable n=1 ideal kink mode is found to couple with the highorder modes and drive them to finite amplitude. The nonlinear phase of the RWM is important for understanding the triggering of disruptions due to the destructive RWM fluctuations. 

PP11.00059: Maxwell Torque Scaling Studies using NIMROD Eric C Howell, Jacob R King, Scott E Kruger Locking of tearing modes is a leading cause of disruptions in tokamaks. Tearing modes are typically born rotating with the plasma; however, external magnetic perturbations exert a breaking torque, slowing the island rotation, and potentially resulting in locking. Future burning plasma experiments will have slow rotation due to their weak injected neutral beam torques relative to their moment of inertia. As such mode locking is of increased concern in these experiments. An important issue for predicting the locking is to quantify the scaling of the Maxwell torque. To address this issue extended MHD simulations, using NIMROD [C.R. Sovinec et al., JCP 2004], are used to study the torque scaling as a function of major radius. A family of similar Lmode equilibria with ITER like shaping, characteristic of the startup conditions, are considered. A heuristic neoclassical toroidal viscosity [T.A Gianakon et al., POP 2002] is used to model the effects of poloidal flow dampening, polarization current enhancement, and bootstrap current generation. The electron dampening rate is used as a tuning parameter to normalize the saturated island width to major radius. The torque scaling in thin, medium sized, and thick islands is considered. 

PP11.00060: Multidevice study of MHD modes locking in tokamaks V. Klevarova, G. Pautasso, H. Zohm, P.C. de Vries, M. Lehnen, T. Markovic, M. Komm, J. Havlicek, G. Verdoolaege, JET Contributors*, EUROfusion MST1 Team+, ASDEX Upgrade Team Tearing modes amplitude is a key ingredient to develop physics based disruption prediction methods. Depending on the experimental situation, these modes may rotate or be locked prior to the disruption, which complicates their amplitude incorporation into a multimachine approach. The aim here is to characterise the mode locking process across several devices. A database of >150 COMPASS, >220 AUG and >40 JET discharges with an initially rotating disruptive mode was therefore assembled. Database entries vary from quasistable NTMs to immediately locking radiative instabilities. The deceleration of an initially rotating resistive mode to the locked state via an interaction with the resistive wall and error fields has been described by a mode locking model in the past^{1,2,3}. Capability of the model to characterize the phenomenon in devices of various plasma sizes under broad distribution of plasma parameters (n_{e}, q_{95}, l_{i }etc.) will be tested. ^{1}M.F.F. Nave et al Nucl. Fusion 30 2575 (1990 ^{2}D.A. Gates et al Nucl. Fusion 36 273 (1996) ^{3}R.J. La Haye et al Nucl. Fusion 46 451 (2006) 

PP11.00061: Multiregion Relaxed MHD toroidal states with flow Robert L Dewar, Zhisong Qu, Naoki Sato, Stuart Hudson, Matthew J. Hole The actionbased formulation^{1 }of Multiregion Relaxed MHD (MRxMHD) encompasses both steadyflow statics, and dynamics on a slower timescale than Taylor relaxation. An extension of the 3DMRxMHDbased equilibrium code SPEC^{3 }to allow plasma flow with reasonably general flow profiles is now under development, but the formulation of Ref. 1, which describes the plasma in each region as an ideal Euler fluid is too general for practical purposes as it allows all the turbulent complexity of such a fluid. This motivates seeking a relaxation model^{ }for fluids that maintains compatibility with idealMHD flowequilibrium theory, at least in the axisymmetric limit.


PP11.00062: On the problem of equilibrium with flow in toroidal confinement systems and intrinsic rotation J. Julio E. HerreraVelázquez Intrinsic rotation is an important stabilizing effect of interest in toroidal confinement devices. It is a highly complex problem, in which many mechanisms are involved, such as collisional moment transport, fluctuation ioninduced Reynolds and Maxwell stress tensors, charge exchange with neutrals, orbit losses, etc. [1]. However, it is usual to base theoretical treatments on equilibria in which flow is usually ignored. When dealing with small aspect ratio configurations, taking flow into account may be necessary. This work is an attempt to modify some of the existing theories when this refinement is included. 

PP11.00063: Ideal magnetohydrodynamic equilibrium expansion about a magnetic axis in a nonsymmetric torus Harold Weitzner, Wrick Sengupta A variant (weitzner Phys.Plasmas 2014) equilibrium representation is employed to construct a a formal expansion of a MHD equilibrium in a topological torus with a given magnetic axis. The lowest order terms are given explicitly and the description of the higher order terms is given. Additionally an examination of the ability to extend the expansion to all orders is presented. The expansion is in terms of the distance from the given magnetic axis. The conditions of quasisymmetry and omnigenity are given in terms of the expanded quantities. Comparison with results of other approaches is also given. 

PP11.00064: Computational study of magnetohydrodynamic equilibria with emphasis on fragility of flux surfaces Eugenia Kim NSLAB, a variant of the NSTAB code, is being developed and employed to examine nonsymmetric magnetohydrodynamic equilibria in a topological torus. The plasma domain is a cube in three space, with periodicity in the y and z coordinates. The code employs the standard variational equilibrium minimization method to obtain the equilibrium state. Studies of the destruction or preservation of flux surfaces, dependent on the choice of boundary conditions, are undertaken, with results being presented. Comparison of cases with zero shear, low shear, and moderate shear are given. 

PP11.00065: Stability of a highbeta, largeaspectratio, toroidally rotating tokamak plasma by the SpectralWebMethod Omar Lopez, Luca Guazzotto Macroscopic flows are present during routine tokamak operation and have been the subject of plenty of theoretical work. In particular, stability magnetohydrodynamic studies can be carried out through the Lagrangian description for the plasma displacement proposed by Frieman and Rotenberg [1]. In this work, we build upon an analytic solution [2] of the GradShafranovBernoulli system for plasma equilibrium with a linearly increasing toroidal flow profile, in the highbeta, largeaspectratio limit for circular and elliptical configurations. By simplifying the eigenvalue problem into a second order, nonlinear, ordinary differential equation for the radial displacement first, we then employ the SpectralWeb formalism [3] to conduct a stability analysis of external modes developed in the presence of ideal and resistive walls. The results generalize the rigid body toroidal rotation scenario considered in Betti’s work [4] and are benchmarked against it.


PP11.00066: Nonsymmetric 3D vacuum magnetic fields with surfaces Wrick Sengupta, Harold Weitzner In this work, we present three different approaches to the question of existence of flux surfaces in a vacuum magnetic field in a low shear stellerator. Our first approach is to demonstrate that a perturbation series in the amplitude of the nonsymmetric components can be carried to all orders by carefully adding certain "resonant fields" as shown in (Weitzner2014). Next, we study small perturbations of an equilibrium with closed field lines. We show that stellarator symmetry plays a crucial role in ensuring existence of surfaces to all orders in the expansion. Finally, we attempt to solve the Cauchy problem by expanding in the distance from a rational flux surface following (Weitzner2016). Since rational surface is a characteristic surface of ideal MHD, we need consistency conditions on the Cauchy data on the lowest order surface. Through a careful examination of the differences in the underlying mathematical structures of the various ideal MHD systems, we show that suppressing magnetic resonances in vacuum fields is far more complicated and involved than force free or MHD with finite beta systems. Weitzner, H. Physics of Plasmas (2014,2016) 

PP11.00067: Investigation of core MHD activities in the high β_{N} plasmas in EAST Xiang Zhu, Long Zeng, Haiqing Liu, Guoqiang Li, Muquan Wu, Di Jiang, Hao Qu, Qing Zang, Bo Lyu, Yao Yang, Yinxian Jie, Xiang Gao Improved Hmode plasmas with high normalized beta (β_{N} > 1.6) have been achieved on EAST tokamak. Weak temperature and density internal transport barriers (ITB) were observed. The main focus is on the influence of the core MHD activities, including fishbones and sawteeth on plasma performance. The electron temperature and the density profile evolutions show both temperature and density ITB maintained during the fishbone activities. Detailed comparisons of the kinetic profiles show trivial changes in the core region during fishbone activities but significant decrease due to sawteeth crash, which also gives possibility to trigger neoclassical tearing modes (NTMs). The safety factor (q) profile, confined by the Faraday rotation measurements from the polarimeter/interferometer (POINT) system on EAST, represents that a flat q profile with q_{0} close to unity can be maintained and a 1/1 fishbone simultaneously exist. Detailed discussions of plasma performance under the same external control parameters will be studied and discussed. 

PP11.00068: Studies of Fastiondriven MHD Instabilities in Heliotron J Equilibrium by ParticleMHD Hybrid Simulation code MEGA Panith Adulsiriswad, Satoshi Yamamoto, Yasushi Todo, Yasuhiro Suzuki, Kazunobu Nagasaki, Shinsuke Ohshima, Hiroyuki Okada, Shinichiro Kado, Takashi Minami, Shinji Kobayashi, Tohru Mizuuchi Understanding of fastiondriven MHD instabilities is crucial for realizing sustainable burning plasma. In this study, MEGA, a hybrid MHD simulation code is applied to Heliotron J, which is a low shear helicalaxis heliotron. MEGA utilizes nonlinear MHD equations for bulk plasma and a drift kinetic equation for fastions. Previously, MEGA has been implemented only in Tokamak and LHD. The objective of this study is to verify the fastion MHD wave resonance in Heliotron J equilibrium by MEGA. The utilized equilibrium has m/n=7/4 magnetic islands at the edge region. This islands are located close to the experimentally observed m/n=2/1 global Alfvén eigenmode (GAE). To simplify the calculation, the coupling between Alfvén eigenmode and magnetic island is avoided. Only eigenmodes in the core region are considered. Two eigenmodes may exist at r/a=0.4: m/n=8/5 toroidal Alfvén eigenmode (TAE) and m/n=5/3 betainduced Alfvénacoustic eigenmode (BAAE). We have found an instability with the dominant harmonic of m/n=5/3 at the BAAE gap location; however, the frequency of the mode is 1 kHz, which is less than predicted value from BAAE dispersion relation (27.4 kHz). The properties of this instability will be discussed and other instabilites will be explored. 

PP11.00069: DriftIdeal MHD Simulations of FlowStabilized ZPinch Plasmas Justin Ray Angus, Mikhail Dorf, Debojyoti Ghosh A number of experimental and theoretical studies suggest that the presence of a modest radial shear in the axial plasma flow velocity can provide stabilization of Zpinch plasmas against the most destructive ideal MHD instabilities (sausage and kink), thereby making the flow stabilized Zpinch (FSZP) configuration attractive for magnetic fusion energy applications [1]. While radial variations in the plasma flow velocity that occur on the pinchsize scale a can stabilize these largescale (k~1/a) MHD modes, weaker shortscale driftwave instabilities that occur on the much smaller gyroBohm scale (k~Cs/Wi) are less affected and can act over time to reduce the velocity shear and degrade the confinement. The effects of these drifttype modes as well as standard ideal modes on the stability of the shearflowed Zpinch configuration are studied in this work via the numerical simulation of the driftideal MHD equations [2] in 2D. The driftideal MHD model is an extension of ideal MHD to include finite ioninertial length/gyrofrequency effects. 

PP11.00070: Updated HITSI3 Thomson Scattering Diagnostic Christopher Everson, Thomas R Jarboe, Kyle D Morgan The Thomson scattering diagnostic on HITSI3 has been modified to enable measurements of electron temperature down to nearly 5 eV. This should allow for up to three simultaneous spatial measurements of T_{e }per discharge. These will be the first Thomson scattering measurements on the inductively driven HITSI3 spheromak. The modification involved installing new filters on the polychromators that bin the Dopplershifted scattered light by wavelength. The filter passbands (and therefore the sampling bins) have been shifted closer to the laser line to increase sensitivity to the colder T_{e }distributions. Preliminary measurements with the new polychromators will be compared with the old polychromator setup to quantify the change in sensitivity. The aim of the new system is to enable both density and temperature measurements on HITSI3. Previous attempts at Thomson scattering measurements on the HITSI3 device indicated temperatures of 10 eV or less, however recent plasma performance achievements may allow for the new Thomson measurements to be made on spheromak plasmas of higher current. 

PP11.00071: Simulations of SIHI Spheromak Current Drive Experiments Thomas Benedett, Christopher Hansen, Thomas R Jarboe The HITSI experiment has demonstrated stable sustainment of spheromaks. Determining how the underlying physics extrapolate to larger, highertemperature regimes is of prime importance in determining the viability of the inductivelydriven spheromak. It is thus prudent to develop and validate a computational model that can be used to study current results and study the effect of possible design choices on plasma behavior. An extended MHD model has been applied to simulate the HITSI and its successor HITSI3 across a range of injector frequencies (14, 36, 53, 68 kHz), and the results of those frequency scans will be shown, detailing general agreement with most experimental trends as well as where and what differences are observed. Behavior of a proposed future design with an alternate injector configuration will also be explored via extended MHD, and comparisons to earlier configurations made. 

PP11.00072: MHD Modeling of Current Drive in HIT Devices with Extended Validation of HITSI3 James Penna, Thomas Jarboe, Kyle D Morgan, Tom Benedett, Aaron C Hossack The Helicity Injected Torus – Steady Inductive 3 (HITSI3) uses Steady Inductive Helicity Injection (SIHI) to drive current within a spheromak plasma via Imposed Dynamo Current Drive (IDCD)[1]. SIHI sustainment and the IDCD model are used as founding principles for a proposed new HIT experiment, the Helicity Injected Torus Technology Demonstration (HITTD), which aims to sustain toroidal current in a closedflux spheromak using SIHI. HIT devices are modeled using the NIMROD MHD code. The most recent design of HITTD is modeled in NIMROD and driven to high enough current gain for closed flux surfaces to form. The properties of the resultant closed flux equilibrium are presented and analyzed with emphasis on scaling to fusion reactor operation. Simulations of recent HITSI3 plasma pulses are also presented to validate new experimental results gained from a recentlyinstalled 3D electron density tomography system. Experimental and synthetic density profiles are examined alongside profiles of currentdriving terms using simulation results to determine the fidelity of the simulation model and study the effects of threedimensional density fluctuations on current drive and sustainment. [1]B. S. Victor et al., Phys. Plasmas 21, 082504 (2014) 

PP11.00073: Numerical studies and validation of nonaxisymmetric perturbations and selforganized spheromak formation in the HITSI and HITSI3 devices. Kyle D Morgan, Thomas R Jarboe, Aaron C Hossack Finitebeta extended MHD modeling using the NIMROD code is validated against experimental results and used to enhance understanding of the details of plasma selforganization, where Hall physics and other twofluid effects are found to be important. The Helicity Injected Torus with Steady Inductive helicity injection experiments use a set of inductively driven helicity injectors to apply oscillating nonaxisymmetric current drive on the edge of the plasma, both forming and sustaining a selforganized, stable, steady state axisymmetric spheromak equilibrium in a central fluxconserving volume. The two devices differ on both the spatial and temporal details of the ACdriven helicity injection but produce similar final plasma equilibrium. It is shown both experimentally and in simulation that a spheromak equilibrium can be formed for every spatial and temporal variation of the helicity injection scheme possible on the experiments, which combine n=1, 2, and 3 toroidal perturbations. While each case forms a similar stable equilibrium, differences in the observed equilibria generated are also seen. The detailed study of these differences through a combination of simulation and experimental probe measurements allow improved understanding of the details of plasma selforganization. 

PP11.00074: Selforganization of stable plasma Thomas Jarboe, Thomas R Jarboe The HITSI experiment inductively drives the edge current and also imposes asymmetric perturbations with the surprising discovery that stable equilibria are sustained. Perturbations cause a force on the current that flattens the current profile of stable equilibria. From developing a physical description of the phenomenon some hypotheses emerge about selforganized kinkstable equilibria: 1. Magnetic plasma relaxes toward a state of minimum energy while conserving helicity. The MECH state is stable. 2. Helicity injection and imposed perturbations may allow the sustainment of stable equilibria with a stepped j/B profile. 3. AC asymmetric helicity injection may stabilize slow growing instabilities through dynamic stabilization. 4. Electron velocity shear may locally stabilize and symmetrize most unstable modes of an MHD kinkstable equilibrium. 5. Pressure driven interchange may flatten the j/Bprofile helping to stabilize kinkmodes. Physical arguments and computational and experimental data will be shown in favor of these hypotheses as well as arguments and data against. 

PP11.00075: Penetration of rotating transverse electric and magnetic fields Peter Jandovitz, Samuel A Cohen Rotating transverse magnetic fields have been used since the 1960s to drive azimuthal current in an axial plasma column. The conditions for penetration and synchronous electron rotation have been previously examined for resistive plasmas extensively. However, penetration of transverse inductive electric fields, which could cause significant ion heating at the magnetic null of a fieldreversed configuration plasma, has not yet been investigated. Here, we compare the penetration of the two types of fields using the kinetic particleincell simulation code, LSP. 

PP11.00076: Twofluid (plasmaneutral) ExtendedMHD simulations of spheromak configurations in the HITSI3 experiment with PSITet Derek A Sutherland, Christopher J Hansen, Aaron C Hossack, Thomas R Jarboe A selfconsistent, twofluid (plasmaneutral) dynamic neutral model has been implemented into the 3D, ExtendedMHD code called PSITet. A monatomic, hydrogenic neutral fluid reacts with an MHD plasma fluid in this model. Density, momentum, and energy are evolved for both the plasma and neutral species. The implemented plasmaneutral model in PSITet is used to simulate decaying spheromak configurations in the HITSI3 experimental geometry, which are compared to twophoton absorption laser induced fluorescence (TALIF) measurements. Validation results between TALIF measurements and PSITet simulations with the implemented dynamic neutral model will be presented. Preliminary plasmaneutral simulations of HITSI3 spheromak plasmas sustained with steady, inductive helicity injection (SIHI) will be presented. Lastly, comparisons between plasma density measurements made with a new tomography diagnostic system and plasmaneutral simulations of driven HITSI3 plasmas will be presented, and potential benefits of possible extensions of the plasmaneutral model will be discussed. 

PP11.00077: Preliminary measurements of electron cyclotron emission from the PFRC II Eugene S Evans, Samuel A Cohen Understanding energy flows in magnetic fusion energy reactors is critical to achieving practical designs. Cyclotron radiation is expected to be an important energy loss channel in reactors utilizing advanced fuels, e. g. DHe3, due to the required core plasma temperatures. Current models for a fullscale reactor based on the Princeton FieldReversed Configuration (PFRC) include predictions for electron cyclotron emission (ECE), though with uncertainties on the order of 10% or more. Properly characterizing the spectrum and intensity of radiation emitted by the PFRC II would improve the accuracy of these models. Results of tracing waves through FRClike equilibria and preliminary measurements of ECE from the PFRC II are presented, along with comments on their applicability to reactorscale FRC models. 

PP11.00078: Overview of C2W FieldReversed Configuration Experimental Program Hiroshi Gota, Michl W. Binderbauer, Toshiki Tajima, Sergei Putvinski, Michel Tuszewski, Sean Dettrick, Artem Smirnov, Matthew C. Thompson, Xiaokang Yang, Alexander A. Ivanov, and the TAE Team TAE Technologies’ research is devoted to producing high temperature, stable, longlived fieldreversed configuration (FRC) plasmas by neutralbeam injection (NBI) and edge biasing/control. The newly constructed C2W experimental device (also called “Norman”) is the world’s largest compacttoroid device andhas the following key upgrades from the preceding C2U device [1]: (i) higher injected power, optimum energies, and extended pulse duration of the NBI system; (ii) installation of inner divertors with upgraded edgebiasing systems; (iii) fast external equilibrium/mirrorcoil current rampup capability; (iv) installation of trim/saddle coils for active feedback control of the FRC plasma; and (v) extensive upgrade/expansion of plasma diagnostic capability. C2W experiments have already produced dramatically improved initial FRC parameters with much higher plasma temperatures (T_{e}>250 eV; total electron and ion temperature >1.5 keV) and more trapped flux inside the FRC immediately after the merger. Plasma duration/lifetime has reached up to ~10 ms via outerdivertor edge biasing. This paper will review highlights of the C2W program, including recently obtained experimental results. 

PP11.00079: Summary of C2W FieldReversed Configuration Experiment Diagnostic Systems and Results Matthew Thompson, Tania Schindler, Hiroshi Gota, Sergei Putvinski, Michel Georges Tuszewski, Michl W Binderbauer, and the TAE Team TAE Technologies, Inc. studies the evolution of advanced beamdriven fieldreversed configuration (FRC) plasmas sustained by neutralbeam injection. Ongoing operations on the new C2W device (also called Norman) focus on FRC heating and diamagnetic current build up [1]. Data on the FRC plasma is provided by a comprehensive suite of diagnostics including over 700 magnetic sensors, four interferometry systems, multichord FIR polarimetry, two Thomson scattering systems, survey spectroscopy measurements, impurity and majority ion CHERS, multiple fast imaging cameras, end loss analyzers, multiple bolometer systems, and fusion product detectors. Many other sophisticated diagnostics are also in preparation and commissioning including: reflectometry, neutral particle analyzers, and FIDA. Most of these diagnostic systems are new designs built using experience and data from the preceding C2U [2] experiment. TAE’s diagnostics development program also works on novel systems including new ways to measure FRC internal magnetic fields. [1] M.W. Binderbauer et al., AIP Conf. Proc. 1721, 030003 (2016) [2] M.C. Thompson et al., Rev. Sci. Instrum. 87, 11D435 (2016) 

PP11.00080: FRC Formation And Translation Experiments On The C2W Experiment Erik Trask, H. Gota, P. Yushmanov, Y. Mok, E. A. Baltz, W. D. Heavlin C2W fieldreversed configuration (FRC) experiments have begun at TAE Technologies [1]. Increased stored energy, improved pulsed power reliability, and dynamic control of magnetic fields have allowed creation of FRC targets with improved characteristics. Parameters achieved so far include relative translation velocities of over 1000 km/s, trapped flux of over 15 mWb, and diamagnetic energy of over 10 kJ. Translation characteristics have been scanned over wide ranges of magnetic fields, including passage through mirror fields of over 0.7 Tesla. Mapping and searching techniques including Optometrist Algorithm [2] stochastic searches have been utilized to determine system functionality and optimal operating settings. A review of achieved initial conditions and experimental observations will be presented. [1] M.W. Binderbauer et al., AIP Conf. Proc. 1721, 030003 (2016). [2] E.A. Baltz et al., Sci. Rep. 7, 6425 (2017) 

PP11.00081: Application of Bayesian inference for reconstruction of FRC plasma state in C2W P. C. Norgaard, E. A. Baltz, M. Dikovsky, I. Langmore, T. Madams, J. Romero, M. C. Thompson, E. Trask, H. Gota Bayesian methods are used to infer Field Reversed Configuration (FRC) plasma properties for the C2W machine at TAE Technologies. The approach starts with a statistical distribution of possible plasma states, where physicallymotivated constraints are imposed through the Bayesian prior. These are processed by a forward model for the relevant instruments to assess agreement with corresponding measured experimental data. The resulting probability distribution, known as the posterior, describes the most likely plasma state and the corresponding statistical confidence. Plasma state reconstruction from multiinstrument Bayesian inference are presented in this study, implemented for the upgraded diagnostics that have come online for C2W. FIR interferometry, Thomson scattering, Bremsstrahlung radiation measurement, and secondary electron emission detection from the neutral beams are used in reconstruction near the FRC midplane. Magnetic probes and imaging from a highspeed camera provide 3D data throughout the main confinement vessel. This study aims to further the understanding of plasma properties and dynamics, such as electron and ion densities, electron temperature, plasma current, and magnetic field topology. Team: Google/TAE 

PP11.00082: The C2W real time inference and plasma control system Jesus Romero, Colin Finucane, Kevin Phung, The TAE Team As Field Reversed Configuration (FRC) discharges in C2W (also known as Norman) last longer than the time constant of the conductive structures external to the plasma, feedback control systems become necessary to maintain the FRC plasma well centered inside the confining vessel. The function of the C2W Plasma Control System (PCS) is both to provide high bandwidth (2.5 MHz) data acquisition of about 400 magnetic signals, and low bandwidth feedback control (40 kHz) of FRC plasma shape and position. In addition, the system capacity allows for future expansion for control of kinetic plasma variables. PCS is a distributed control system built from a set of data acquisition modules and control units from Speedgoat, programmed using Matlab scripts and Simulink models. This allows for fast prototyping and testing of observers and control algorithms, a useful feature for plasma control systems research. Examples of these are a low latency Bayesian observer for plasma equilibrium and advanced control algorithms for plasma shape, position and stability. First operational experience with the system is presented and discussed. 

PP11.00083: 3D neutral distribution in C2W determined from visible imaging and interpretive modeling Erik M. Granstedt, Kan Zhai, Bihe Deng, Deepak K Gupta, Sean Dettrick, Dima Osin, Thomas J. Roche, and the TAE Team The C2W device\footnote{M.~Binderbauer, et~al. AIP Conference Proceedings \textbf{1721}, 030003 (2016)} is equipped with eight 1.6 MW neutral beams which inject largeorbit fast ions to sustain a fieldreversed configuration embedded within an axisymmetric magnetic mirror. Collisional energy transfer from fast ions is intended to be the primary source of heating of the bulk plasma; therefore, the spatial and velocity distribution of fast ions strongly affects the overall power balance and understanding fast ion loss is critical. At typical injected energies (15 keV) and external fields (0.71 kG) fast ions sample the core, scrapeofflayer, and diffuse outeredge plasmas where they can be lost via chargeexchange with neutrals. Careful vacuum practices and titanium gettering successfully reduced neutral recycling from the vessel walls. As a result, warm neutrals generated from beam capture via chargeexchange with bulk plasma ions constitute a large fraction of the remaining neutrals. Balmer$\alpha$ emission measured with a filtered highspeed camera is used with DEGAS2 neutral particle modeling to reconstruct the strongly nonaxisymmetric neutral distribution. This distribution is then used with Monte Carlo modeling to estimate the chargeexchange loss rate of fast ions. 

PP11.00084: Diagnosing the MHD stability of an FRC with neutral beam shine through on C2W James Titus, Richard M Magee, Sergey Korepanov, and the TAE Team Heating, current drive, and partial fueling from neutral beam injection are essential to sustainment of C2W fieldreversed configuration (FRC) plasmas.^{1} Eight beams are injected offaxis, just outside of the axial center of the FRC. After traversing the plasma, the uncaptured components of each beam interface with a secondary electron emission (SEE) detector array installed in the beam dump and the shine through can be measured. Since beam capture is dependent on plasma density, any changes in density within the beam path are reflected in the measurement. Due to the geometry of beam injection, changes outside of the FRC core can be monitored. During the n = 1 and 2 instabilities, the plasma wobbles and the density of the plasma in the beam path changes. Without effective stability control, it has been seen that when beam shine through reaches a minimum, the FRC plasma appears to start shrinking and the n = 1 instability grows, after which the FRC dies out due to the instability or keeps rotating with somewhat reduced/saturated mode growth.
[1] M.W. Binderbauer et al., AIP Conf. Proc. 1721, 030003 (2016). 

PP11.00085: Measurements of the Energy Distribution of Ions Lost From the ScrapeOff Layer of C2W Martin E. Griswold, Matthew C. Thompson, Kurt Knapp, Blake Koop, William Thornton, and the TAE Team We report on measurements of the ion energy distribution function (IEDF) of ions lost from the scrapeoff layer (SOL) of the C2W experiment [1] at TAE technologies. C2W consists of a field reversed configuration (FRC) core plasma surrounded by a mirrorconfined SOL on open field lines. The open field lines extend past a mirror at either end of the central vessel and then expand by a factor of B_{max}/B_{min}~30 into large divertor vessels where they terminate on sets of concentric circular electrode plates. The expanding magnetic field in the divertors is designed to impede cold electrons generated at the edge of the machine from flowing back into the central vessel. This should allow an ambipolar potential to develop inside the mirrorconfined region of the SOL and reduce electron heat transport out of the region. We used electrostatic ion energy analyzers mounted on the divertor electrode plates [2] to measure a driftingMaxwellian shaped IEDF. The results show that an ambipolar potential develops in the central vessel and give insight into electron heat transport on the SOL. [1] M. Binderbauer, et. al. AIP Conference Proceedings 1721, 030003 (2016) [2] M. E. Griswold et. al., to be published in Rev. Sci. Instrum. 

PP11.00086: Langmuir Probe Characterization of the C2W ScrapeOffLayer Plasmas Ami M DuBois, Thomas Roche, Kurt Knapp, Ray Michel, and the TAE Team The C2W experiment is a fieldreversed configuration (FRC) which uses neutral beam injection and an edge biasing scheme to suppress turbulence and stabilize the plasma. The FRC core is surrounded by open field lines in the edge region of the confinement vessel (CV), called the scrapeofflayer (SOL), which terminate on electrode plates located in the inner and outer divertors. Therefore, settings in the divertors can significantly affect the plasma conditions and stability in the SOL. A motorized triple Langmuir probe with 24 inches of travel has been installed on the CV, 66 cm from the midplane to make critical measurements of the SOL plasma parameters. Characterization of the electron density (n_{e}), electron temperature (T_{e}), floating potential, plasma potential, and edge fluctuations in the C2W SOL are presented. Initial measurements show SOL T_{e} ~20 eV as the FRC is formed, after which T_{e} gradually decreases, and SOL n_{e} ~10^{18} m^{3}, consistent with Thomson Scattering and FIR diagnostic data measured at the CV midplane. Finally, details of a design for a new insertable probe platform system and initial measurements in the C2W inner divertor will be discussed. 

PP11.00087: Electron temperature and density profiles of C2W FRC plasmas in different experimental configurations Kan Zhai, Tania Schindler, Angelica Ottaviano, Eli Parke, Matthew C Thompson One of the experimental goals of the recently constructed C2W advanced fieldreversed configuration (FRC) [1] experiment is to increase the plasma electron temperature. The unique design of C2W includes additional inner divertors on both sides of the central confinement vessel, each with bias electrodes and flexible field configuration that determines the plasma edge condition. C2W also has increased total neutral beam power, higher pulsed formation fields for creating hotter colliding compact toroids at startup, and the ability to ramp up the equilibrium field during FRC confinement. The C2W Thomson scattering system, built in parallel with the C2W device, plays a critical role in characterizing C2W plasma performance by measuring the electron temperature and density profile evolution for both the FRC core plasma and the open field region jet plasma. The effects of different experimental configuration on plasma electron temperature will be presented and discussed. [1] M.W. Binderbauer et al., AIP Conf. Proc. 1721, 030003 (2016) 

PP11.00088: Open field line region electron temperature and density profiles in C2W via Thomson scattering E. Parke, A. Ottaviano, T. Schindler, K. Zhai, M. C. Thompson, and the TAE Team C2W is a recently constructed fieldreversed configuration (FRC) plasma experiment which aims to increase plasma lifetimes and rampup electron temperatures with respect to its predecessor C2U. A mirrorconfined scrapeofflayer (SOL) encloses the central FRC and collapses into axial plasma jets along open field lines on either side of the central vessel. These connect to biasable electrode plates in the inner and outer divertors allowing for a range of magnetic field configurations and plasma edge conditions to be explored. A new jet Thomson scattering (TS) diagnostic capable of acquiring 4 temporal measurements at a repetition rate of 100 Hz across 5 radial locations of C2W’s south jet region is under construction. Measuring the properties of the plasma jet is important for studying the FRC translation, confinement and sustainment, and for determining the conditions and parameters needed for increasing the FRC lifetimes and electron temperatures. System design, status, and results are reported and discussed. 

PP11.00089: Results of midplane and Jet region interferometry on the C2W FRC experiment Roger J Smith, Eli Parke, Michael Beall, Bihe Deng, John Kinley, and the TAE Team TAE Technology’s C2W experiment has been operational for over 18 months and has produced longlived fieldreversed configuration (FRC) plasmas. Plasmas are sustained by fixed and variable energy neutral beam injection (NBI) ^{ }sources. Multichord FIR interferometry of the FRC at the midplane of the confinement vessel is essential for operations, and interferometry in the mirror region of the confinement vessel quantifies the plasma outside the separatrix (last closed flux surface) which consists of: the plasma outflow through the X points (Jet plasma), the scrape off layer (SOL) plasma, and recycling from the inner and outer divertors. The magnetic field outside the FRC can be shaped and terminated on material limiters in a number of different ways. The plasma along open field lines terminating on the electrodes of the divertors can also be biased providing a wealth of variability for the boundary conditions of the FRC. Interferometry measurements of the distribution of density within and external to the FRC for various C2W operational programs are presented and the implications of the observed behavior on the performance of the plasma is discussed.


PP11.00090: Measurement and Analysis of Z_{eff} in the C2W FieldReversed Configuration Plasma Experiment Marcel Nations, Deepak Gupta, Nathan Bolte, Matthew C. Thompson, and the TAE Team The effective ionic charge (Z_{eff}) is an important parameter which serves as a quantitative proxy for impurity levels in fusion plasmas. A study of the spatial and temporal evolution of Z_{eff} helps elucidate the mechanisms that drive impurity generation and transport. In C2W, Z_{eff} is determined from measurements of visible and nearinfrared bremsstrahlung light. Balmeralpha (D_{α}) neutral detectors are utilized for pollutant removal. In this work, Z_{eff} behavior for different machine settings and wall conditioning experiments are investigated and discussed. 

PP11.00091: Correlations between Impurity Ion Tangential Velocities and Electron Density Rotational Modes in the C2W Experiment Michael Beall, Deepak Gupta, and the TAE Team The C2W experiment is a FieldReversed Configuration plasma device directed towards studies of beamdriven, magnetically confined fusion plasmas. As part of the upgrade from the preceding C2U device, new magnetic systems, more powerful neutral beams, internal expansion chambers, and biasing electrodes were added to improve energy confinement times, particles temperatures, plasma stability and control. Many interesting dynamics arise from the rotational modes of the plasma, one of which being the socalled N=2 elliptical mode. This plasma deformation arises nondestructively during many high energy pulses, and is observed on a range of diagnostics. The ability of the new iChers spectrometer to measure temporally and spatially resolved impurity ion velocities and temperatures provides an interesting opportunity to observe the relationship between the plasma rotational velocity and some of its rotational modes. The spectrometer provides a velocity resolution of 4.0 km/s at short wavelengths, such as for 278.1 nm (OV), and 1.5 km/s at longer wavelengths like 656.52 nm (Da). 

PP11.00092: Ion Flow Measurement on the C2W Open Field Line Plasma Daniel Sheftman, Nathan Bolte, Deepak Gupta, Matthew C Thompson, TAE Team Accurate operation and high performance of the open field line plasma surrounding the Field Reversed Configuration (FRC) is crucial to achieving the goals of successful temperature ramp up and confinement improvement on C2W. Of particular importance is the control of the end loss plasma flow from the FRC core towards the divertor plates and mitigation of the flow of impurities back into the FRC plasma. A highresolution Doppler spectrometer was used to measure impurity ion flow in both directions at different locations across the open field line plasma from a position in the mirror region between the central FRC confinement vessel and the inner divertor. Impurity ion velocity profiles are presented for various experimental conditions. 

PP11.00093: Advanced Diagnostics for the Wavenumber Spectrum of Density and Magnetic Field Fluctuations in the C2U and C2W FRCs Lothar W Schmitz, Bihe Deng, Michael Beall, Hiroshi Gota, Matt Thompson, Calvin Lau, Toshi Tajima, Michl Binderbauer An advanced multichannel combined Doppler Backscattering (DBS)/CrossPolarization (CPS)[1] diagnostic for the C2W FieldReversed Configuration (FRC) will be discussed, allowing simultaneous measurements of the wavenumber spectrum of density fluctuation and magnetic fluctuations. Crosscorrelation analysis on ñ and B_{r} should be possible as the backscattered Omode DBS return and the backscattered Xmode CPS signal originate essentially from the same scattering volume. GENRAY ray tracing predicts that magnetic fluctuations with 2 ≤ k_{tor}rho_s ≤ 50 can be accessed in the FRC core and scrapeoff layer (SOL). DBS data from the C2U FRC already show absence of ionscale density turbulence in the FRC core. Global gyrokinetic simulations attribute core stability to Finite Larmor radius effects, short fieldline connection length, and favorable magnetic field gradient. Transport analysis indicates nearclassical core ion thermal diffusivity. In contrast, multiscale turbulence including shortscale electron modes is observed via DBS in the mirrorconfined SOL plasma, in agreement with global gyrokinetic simulations predicting unstable driftinterchange modes for k_{tor}rho_s > 1.5. [1] X.L. Zou et al., Phys. Rev. Lett. 75 109093 (1991); [2] L. Schmitz et al., Nature Comm. 7 13860 (2016). 

PP11.00094: The C2W Experimental Device Fueling Systems Overview Thomas Roche, Tadafumi Matsumota, Ian Allfrey, Dima Osin, Martin Griswold, Tom Hurn, Lloyd Brown, and the TAE Team The experimental goals of the C2W program are to demonstrate the ability to heat and maintain a fieldreversed configuration (FRC) plasma to a total temperature of several keV for a period of up to 30 ms. As energy confinement times are improved, the particle loss rate will become the dominant limiter of plasma lifetime. In order to mitigate this loss channel, several refueling methodologies have been implemented on C2W. They are: compact toroid injection (CTI), pellet injection, and gas puffing. Each of the two CTI systems is capable of injecting up to 5 CTs over the course of a single shot. The pellet injector launches cryogenically frozen pellets of deuterium from one end of the confinement vessel, through the FRC’s Xpoint and into the core. By aiming the pellets such that they miss the beams, ablation of the pellets external to the FRC is minimized. Puff valves placed in strategic locations along the vessel add neutral gas to the scrapeofflayer (SOL). This keeps enough plasma outside of the FRC so good electrical connection with edge divertors is maintained. Each refueling method can provide a sufficient number of particles to overcome the particle loss rate. However, the regions of effective fueling varies between the systems. 

PP11.00095: Initial Results of Multipulse Compact Toroid Refueling in the C2W FieldReversed Configuration Ian A Allfrey, Tadafumi Matsumoto, Thomas Roche, Hiroshi Gota, Tomohiko Asai, fumiyuki Tanaka, and the TAE Team One of the limiting factors in the lifetime of a fieldreversed configuration (FRC) is particle loss. To refuel the longlived FRC plasma in the C2W experiment a multipulse compact toroid injector (CTI) has been developed. Refueling is accomplished with two radially oriented magnetized coaxial plasma guns (MCPG), diametrically opposed on the midplane of the confinement vessel. The MCPG consists of puff valves, a quasiDC ironcore magnet providing the compact toroid’s (CT) stuffing flux, a preionizer system to improve breakdown and decrease jitter, in addition to coaxial electrodes where the CT is formed and accelerated. These systems allow for the creation of a relatively hot spheromaklike CT, while limiting excess neutral gas. The multipulse capability is achieved with individual pulsed power supplies for each CT for a total of 5 CT’s from each of the two injectors at a repetition rate up to 1kHz. Initial results, including CT parameters and effects on the FRC will be presented. 

PP11.00096: Increased ionization efficiency for high performance CT injection Fumiyuki Tanaka, Tomohiko Asai, Thomas Roche, Ian Allfrey, Hiroshi Gota, Tadafumi Matsumoto, Toshiki Tajima, and the TAE Team A magnetized coaxial plasma gun (MCPG) is one of the devices used to generate and accelerate a compact toroid (CT) with a spheromaklike magnetic configuration. A typical MCPG consists of a set of axisymmetric cylindrical electrodes, a bias coil, and gaspuff valves; and it requires excessive neutral gas to obtain breakdown. The excess gas degrades the performance not only of the generated CT but also of the target plasma. By using a preionization (PI) system (a miniature gun that is installed radially at the same cross section as the gaspuffing ports) we have succeeded in reducing the amount of neutral gas required (~40%) for breakdown, which results in improved performance of ejected CTs [1]. For further improvement of the CT performance, we focus on the gas flow and its spatial distribution in the miniature gun as well as MCPG. The breakdown condition of the miniature gun is optimized by changing the distance between electrodes and varying the amount of initial enclosed gas. A simulation of the gas flow is conducted to optimize the geometry of gas inlets on the miniature gun. We will present an updated PI system and effects on the ejected CT. [1] T. Edo et al., J. Plasma Fusion Res. 13, 3405062 (2018). 

PP11.00097: Simulation of FRC Equilibrium and Global Stability Sean A Dettrick, Francesco Ceccherini, Laura Galeotti, Kevin Hubbard, Daniel C Barnes, and the TAE Team A FieldReversed Configuration (FRC) is a high beta selforganized plasma where the current which closes the field lines is carried by the plasma itself. The shape and position of the closed field line region is determined by the external magnetic field pressure and by the profile of plasma pressure inside the separatrix and in the scrapeoff layer. The internal plasma pressure profiles affect the stability of the plasma to global (low order) modes. Three external actuators which also affect the global stability of FRCs include the external magnetic coils, neutralbeam injection which creates a population of fast ions, and concentric electrode biasing. We use optimization techniques to fit an FRC equilibrium code to the experimental diagnostics of typical C2W discharges. We use the generalized Ohm’s law hybrid PIC code, FPIC, to study the global stability of the resulting FRC equilibria, subject to the three external actuators. The results are used to assist with interpretation of C2W experimental results. The simulations were performed at ALCF using computer time provided by the 2018 INCITE program. 

PP11.00098: Simulations of edge biasing and rotation in the C2W FRC experiment using the Q2D code Marco Onofri, Sean Dettrick, Daniel Charles Barnes, Peter Yushmanov, Toshiki Tajima, and the TAE Team We study the effects of end shorting and electrostatic biasing in simulations of the C2W Field Reversed Configuration experiment using the Q2D code. Q2D is a 2D MHD code, which includes a neutral fluid and separate ion and electron temperatures, coupled with a 3D Monte Carlo code, which is used to calculate source terms due to neutral beams. The model includes the Hall term in Ohm’s law. We modified the boundary to impose different conditions on the radial electric field and we studied the effect of end shorting and electrostatic biasing. The shorting of open field lines at the external boundary generates a toroidal magnetic field and the propagation of a torsional Alfven wave. This modifies the radial electric field along the open field lines and makes the SOL plasma rotate in the ion diamagnetic direction. The plasma rotation can also be controlled by applying a finite radial electric field at the boundary to simulate the effect of electrode biasing. We observe the penetration of this rotation across the separatrix into the closed field lines by viscosity. The effect of the neutral beams on the rotation is also investigated. 

PP11.00099: Onset of Tilt Instability in FRC Plasmas Francesco Ceccherini, Laura Galeotti, Sean Dettrick, Daniel Barnes, Kevin Hubbard, and the TAE Team Tilt instability in FRC plasmas is a wellknown MHD phenomenon that has been extensively investigated over the years by different authors and an empirical scaling law of the numerical growth rate versus the plasma E/S* parameter has been discussed in the literature. FPIC, TAE Technologies’ proprietary hybrid code, was also recently deployed to study the n=1 toroidal modes as tilt, radial shift and interchange. In spite of the investigations already carried out what is the exact onset mechanism and what are the plasma structures which characterize the very early phase of the tilt instability remain largely unknown and any possible investigation requires very large computational resources. Thanks to computing resources provided at ALCF by the 2018 INCITE program it has been possible to utilize HPC capabilities and apply FPIC at unprecedented levels of resolution. Detailed plasma structures at tilt onset and subsequent times are presented and discussed. 

PP11.00100: Reconstructing FRC equilibria from experimental data Loren C Steinhauer, Thomas Roche, Joshua Steinhauer, TAE Team The magnetic structure of FRCs cannot be measured directly by existing diagnostics. A new tool finds the structure based on field measurements at the vessel wall. The first step is data conditioning, finding smooth fits to the data, i.e. the excluded flux radius and wall magnetic flux, both as functions of the axial coordinate. Distilled from these are six parameters, three each from the excluded flux and wall flux profiles. The second step is the equilibrium finder, assuming a static equilibrium (GradShafranov, “GS” equation). The inputs to GS system are the pressure vs flux function and the wallflux boundary condition. The pressure is expressed as one function family and the wall flux as another. Both families have three adjustable parameters for a total of six. Finally, a twolevel iteration finds the solution: the inner loop is a standard relaxation algorithm that updates the flux function; the outer loop iterates the six adjustables, targeting the six parameters distilled by data conditioning. The result is the 2D structure of the flux variable. Extracted from this are various properties of interest, e.g. trapped flux, fraction of plasma current flowing inside the separatrix, as well as stability indices for interchange and tearing. 

PP11.00101: Effects of Rotation on Turbulent Transport in Field Reversed Configuration Jian Bao, Calvin K Lau, Daniel Fulton, Zhihong Lin, Toshiki Tajima The global field reversed configuration (FRC) geometry is incorporated in the gyrokinetic code GTC by using a fieldaligned mesh in cylindrical coordinates, which enables the global simulations coupling the FRC core and scrapeoff layer (SOL) across the separatrix and from divertor to divertor. Magnetic function is used in the cylindrical coordinates to guarantee divergencefree of the magnetic field and to facilitate the construction of the global fieldaligned mesh. This global particle code has been successfully applied for linear drift wave simulation in FRC. Furthermore, a new spacecharge 1D code for sheath simulation is developed, which can provide the boundary condition for the global simulation with sheath effects and divertor biasing voltage. The effects of plasma rotation due to the external applied biasing voltage on the linear drift wave instability and transports are investigated in this work. 

PP11.00102: CrossSeparatrix Simulations of Turbulent Transport in the FieldReversed Configuration Calvin K Lau, Daniel Fulton, Jian Bao, Zhihong Lin, Toshiki Tajima, Lothar W Schmitz, and the TAE Team Experimental progress by TAE Technologies has led to fieldreversed configuration (FRC) plasmas with lifetimes of several milliseconds. Doppler Backscattering (DBS) measurements of C2U show that density fluctuations in the core and scrapeoff layer (SOL) regions are distinct: core fluctuations are consistently low in amplitude while SOL fluctuations have large amplitude at ionscales and decrease towards electronscales. In qualitative agreement, local linear simulations using the Gyrokinetic Toroidal Code (GTC) show the absence of instability in the core and the presence of instability in the SOL. Using the crossseparatrix particleincell A New Code (ANC), we address microturbulence in a global FRC geometry. Global simulations show fluctuations spreading from SOL to core with saturated core fluctuations an order of magnitude lower than the SOL. Simulations, domain limited to the SOL, show saturation at around eφ/T_{e}~O(10^{2}) with an inverse spectral cascade. These features remain present in more realistic global crossseparatrix simulations and contribute to the fluctuation spectra evolving towards the robust SOL and quiescent core spectra, consistent with experimental DBS measurements. 

PP11.00103: Numerical Model Developments of A New Code (ANC) for Fullykinetic Ion Simulation of Turbulence in C2W Daniel Fulton, Calvin K Lau, Jian Bao, Zhihong Lin, Toshiki Tajima, and the TAE Team A principal objective of C2W, the latest device at TAE Technologies, Inc. is to better characterize turbulencedriven particle and energy transport in beamdriven fieldreversed configuration (FRC) plasmas. Doppler Backscattering (DBS) measurements on C2U, the predecessor to C2W, show the absence of low toroidal wavenumber turbulent fluctuations in the FRC core^{[1]}. Gyrokinetic simulations agree qualitatively, and demonstrate stabilization of these core fluctuations via several mechanisms including large ion Larmor radius, negative radial magnetic field gradient, and short fieldline connection length effects^{[2]}. Upgrades to the diagnostic suite of C2W, including an expanded FarInfrared Interferometer system and a planned combination DBS and CrossPolarization Scattering diagnostic, along with refinements to the turbulence code, A New Code (ANC), will enable detailed experimentsimulation crossvalidation. In this work, model developments to ANC’s fullykinetic ion scheme, including a field aligned mesh and a fluxbased density advance are presented with benchmarks. Plans and early progress of validation efforts with C2W experimental data will also be discussed. ^{[1]} L. Schmitz et al, Nat. Commun. 7, 13860 (2016). 

PP11.00104: A BeamFusionTriggered Transmutator; Transparent, Monitored and Controlled Realtime Ales Necas, Toshiki Tajima, Michl Binderbauer, Gerard Mourou, Sydney Gales, Maurice Leroy, Joshua Tanner, Kaleb Hatfield, and the TAE Team We propose a laserdriven [1,2] or electrostatic driven [3] deuteron beam for the purpose of generation of high neutron rate to incinerate minor actinides and transmute fission products. The deuteron beam is generated in the energy range of 150200 keV and is injected into a tank filled with tritium gas or onto a TiT substrate producing DT fusion neutrons. The neutron generating tank (either T gas or TiT foil) is surrounded by a mixture of FLiBe (2LiFBeF_{2}) molten salt eutectic and minor actinides (MA). The FLiBE/MA concentration and machine geometry is optimized to run the transmutator by alternating between subcritical and delayed neutron critical states. Simulation using the MCNP code of the startup phase as well as MA burnup rate and fission product removal will be presented together with passive and active spectroscopy.
[1] Steinke, S., Henig, A., Schnürer, M., Sokollik, T., Nickles, P.V., Jung, D., Kiefer, D., Hörlein, R., Schreiber, J., Tajima, T. and Yan, X.Q., 2010. Laser and Particle Beams, 28(1), pp.215221.
[2] Zhou, M.L., Yan, X.Q., Mourou, G., Wheeler, J.A., Bin, J.H., Schreiber, J. and Tajima, T., 2016. Physics of Plasmas, 23(4), p.043112.
[3] Davydenko, V. I., & Ivanov, A. A. (2004). Review of scientific instruments, 75(5), 18091812.


PP11.00105: Fusion Enhancement from Bunched Ion Beams Bradley Nicks, Toshiki Tajima, Ales Necas, and the TAE Team Using a 1D PIC simulation, the potential for fusion enhancement through injection of an ion beam with density modulation (“bunching”) is demonstrated. The beam is composed of protons, and the background is composed of homogeneous deuterons and electrons in a uniform magnetic field, approximating the scrapeofflayer (β ≈ 0.1) in the FRC (fieldreversed configuration) of the C2U experiment. First, nearperpendicular angles of beam injection and wave propagation are identified as best for producing fast ions. This fastion tail is created by beamdriven IonBernstein (IB) modes through a coherent TajimaDawson wakefieldlike mechanism. The DD fusion reactivity is calculated from the deuteron velocity distribution and normalized with respect to the initial thermonuclear value to quantify fusion enhancement. Next, the fusion enhancement is calculated for an array of beam energies, revealing a powerlaw relationship. Finally, the beam is initialized with density bunching with wavelength matching that of the fastestgrowing IB mode, and the scan over beam energies is repeated. The resulting fusion enhancement is found to exceed that of the unbunched case by as much as a factor of ≈ 30 for roughly v_{b} < 32v_{th}, beyond which the mode structure evolves away from IB modes. 

PP11.00106: Effect of discharge polarity reversal on the selfexcited dust density waves Surabhi Jaiswal, Mikhail Pustylnik, Sergey Zhdanov, Hubertus Thomas We report on the observation of the self excited dust density waves in dc discharge plasma using the PK4 facility. In the experiment, the trapped microparticles cloud was released to drift in a dc discharge of negative and, after some seconds, positive polarity. A DC plasma containing a drifting microparticle cloud was found to be asymmetric with respect to discharge polarity reversal in terms of microparticle drift velocity and plasma emission in accord with [Zobnin et.al., Phys. Plasmas 25, 033702 (2018)]. In addition to that, asymmetry in the selfexcited wave pattern was observed. Also, after the polarity reversal, the wave pattern exhibited several bifurcations. These bifurcations are mainly observed in the head of the microparticle cloud. We show that spatial variations of electric field inside the drifting cloud play an important role in the formation of the wave pattern. 

PP11.00107: Measuring the particle charge in the bulk of a complex plasma Uwe Konopka, Edward E Thomas, Dylan Funk, Brandon D Doyle, Jeremiah D Williams, Christina Knapek, Hubertus Thomas A complex plasma consists beside electrons, ions and neutrals also of a more massive, often purposely introduced component, the charged dust (nano/microparticles). Its acquired charge is a result of the dust—plasma interaction. Due to the relative high dust particle mass, the dynamics of the combined (complex) plasma system, is governed by the dust inertia. This allows to study the complex plasma at the level of the motion and positions of the individual dust particles. A major factor also plays the dust charge. It is often estimated theoretically using orbit motion limited (OML) or similar theories that rely on a background plasma model as well as several crucial assumptions. Experimental determination of the charge is difficult and thus rare, especially for particles in the bulk plasma. In this paper we will discuss an approach to determine an effective dust particle charge in the discharge bulk by analyzing the individual particle motion. We will utilize a freefall experiment facility for complex plasma, such as the international space station experiment PK4, to get access to particle motion in the bulk of the discharge. 

PP11.00108: Useful plasma instabilities for plasma energetics? Aleksandr Mustafaev, Artem Grabovskiy, Vladimir Sukhomlinov, Boris Klimenkov, Victor Kuznetsov Nowadays, thermionic plasma devices based on CsBa filling are promising for cosmic and earthbased nuclear power industry. The results of the research into plasma’s electro kinetic parameters of Knudsen highcurrent diode and triode switching devices are presented in this talk: It has been established, that current modulation in both devices is formed as result of plasma structure generation in the electrode gap without applying any external forces. Such structures develop due to electron instabilities in plasma. Unique regimes for effective grid discharge quenching were attained: the increase in the modulated power is accompanied by the decrease in the power consumption for controlling the current in the triode switching devices. Unprecedented energy parameters were obtained: stable frequency modulation in the range from 1 to10 kHz, an anode potential of 50 V, the electric power density of 5 kW/cm^{2 }and the efficiency more than 95%. The experiments on the CsBa Knudsen diode demonstrate the feasibility of creating a full current modulation at an ignition voltage of 5…6 V and a discharge current density of ~10 A/cm^{2}. At a gap of 0.2…2 mm, a stable current and voltage modulation of 5…20 kHz frequency exists in a Cspressure range from 1.5·10^{3} to 3.5·10^{3 }Torr. 

PP11.00109: Modeling of an argon fluoride single pass amplifier Tzvetelina B Petrova, Matthew Wolford, George M Petrov, Matthew Myers, John L Giuliani, Andrew J Schmitt, Steve Obenschain The US Naval Research Laboratory is developing a repetitively pumped electronbeam ArF* laser based on Electra, which could be the ideal driver for direct and indirect drive for inertial confinement fusion. A kinetics model for the ebeam pumped ArF* laser has been initiated based on the existing Orestes model, initially developed for the KrF* laser at NRL [1]. Uncertainties in many reaction rates and unknown lasing efficiency motivate our basic research program. Here, the existing model was modified to include the ArF2 plasma chemistry and rates from a Boltzmann kinetics model [2]. We report on the results for a single pass amplifier with an external laser source with different intensities. The small signal gain, nonsaturable absorption, and saturation intensity of ArF* as a function of applied ebeam power, gas pressure and composition were calculated and compared with the results from experiments. This research enables understanding of power and particle balances, evaluates the extracted laser intensity and intrinsic efficiency as a function of the ebeam power deposition, and further develops the ebeam technologies. 

PP11.00110: A repetitive nanosecond pulse generator with photoconductive semiconductor and application for atmospheric plasma jets Jinshui Xiao, Chongbiao Luan, Xun Ma, Chuanwei Wang, Hongtao Li In this paper, a compact repetitive nanosecond pulse generator is designed for exciting the atmospheric pressure plasma jets (APPJ) in noble gases. To realize the ultrashort pulse output, a novel Si photoconductive semiconductor switch (PCSS) with reflected cavity and two pulsed formed lines were used. Based on the Blumlein topology, the nanosecond pulse generator can produce repetitive pulses with output voltages of up to 15kV, pulse width of ~7ns, and pulse repetition frequencies of 1Hz~1kHz. Using the designed repetitive nanosecond pulse generator, the characteristics of the APPJ are investigated by measuring the voltages and currents and obtaining images of the discharges. Experimental results show that the nanosecnod pulsegenerator has been successfully used to sustain stable APPJs in helium. The length of plasma plume is over 2cm. Furthermore, the effects of flow rate, the applied voltage, and the pulse frequencies on the He APPJs are investigated. 

PP11.00111: Adaptive Level Grouping for ComplexityReduced, CollisionalRadiative Models Richard J E Abrantes, Robert S Martin, Eder Sousa Accurate timedependent modeling of atomic kinetics may require many atomic levels and transitions that can exacerbate computational times. Complexityreduction algorithms were therefore applied to ameliorate the compute times associated with solving the atomic levels' coupled rate equations. However, recent analysis of these reduction algorithms show that adaptive levelgrouping strategies are needed to capture the atomic kinetics evolution with limited user intervention in the construction of atomic groups.^{1} In this work, a complexityreduced, collisionalradiative model was improved by incorporating clustering algorithms to automate the levelgrouping process. The grouped levels were then utilized in the CR model through Boltzmann group descriptions developed by Le et al.^{2} Preliminary results will show the ability of clustering algorithms to construct atomic groups that lend well to the use of the Boltzmann grouping technique. ^{1 }Abrantes et al. JQSRT 216, 4755 (2018) Distribution A: Approved for public release; unlimited distribution, PA (Public Affairs) Clearance Number 18366 

PP11.00112: Probe measurements at higher pressure Vladimir I. Demidov, Mark E. Koepke, Iya Kurlyandskaya, Mikhail Malkov Existing theories and previous probe measurements of electron distribution functions (EDF) at higher gas pressure are reviewed. An explanation of whether or not the measurements are realizable and reliable, an enumeration of the most common sources of measurement error, and an outline of proper probeexperiment design elements that inherently limit or avoid error are presented. Recent EDFmeasurement developments in higherpressure plasma conditions, including electron spectroscopy analysis with a large wall probe, are discussed. A short (without positive column) dc discharge with cold cathode and conducting walls was used in experiments at gas pressures of a few Torrs. For the investigated conditions, the plasma is collisional. It is experimentally shown that the EDF is proportional to the second derivative of electron current with respect to the probe potentials (as in collisionless theory). EDF measurements conducted in HeliumArgon gas mixtures with percent composition of Argon from 0.002% to 5% will be presented, as will the demonstration of currentvoltage calibration. 

PP11.00113: Time dependent metastable dynamics in low temperature argon plasmas. Ivan Arnold, Stuart Loch, Connor Ballance, Edward E Thomas In the development of optical emission spectroscopy (OES) based plasma diagnostics, it is critical to have a detailed understanding of the atomic processes that give rise to the emission of light. It is known that relative metastable population abundances in a plasma (the socalled “metastable fractions”) play an important role in the population of excited states. Typical rate coefficients for excitation from metastable states are large compared to coefficients for ground state excitation. Thus, metastable excitation can play a large role in the spectral emission of a plasma, even when the relative population of these states is small. We report on recent discoveries with regards to the evolution of metastable states in low temperature argon plasmas, using atomic data from a BreitPauli RMatrix with PseudoStates (BPRMPS) calculation and a Generalized Collisional Radiative (GCR) model. We show that the time dependent evolution of metastable populations can impact relative line heights from spectral emission, and discuss the impact this effect can have on line ratio diagnostics using OES. Finally, we discuss when metastable fractions can be well approximated by their equilibrium values. 

PP11.00114: Collisionalradiative modeling on optical emission spectroscopy for argon plasmas DuckHee Kwon, KilByoung Chai, Min Park Optical emission spectroscopy (OES) which is comparatively simple, versatile, and nonintrusive, has been widely used in diagnostics to lowtemperature plasmas such as capacitivelycoupled plasma (CCP) and inductivelycoupled plasma (ICP) for their numerous applications in analytical chemistry and microelectronic processing. The plasma parameters such as electron temperature and density can be determined by the OES combined with collisionalradiative modeling (CRM) for the population kinetics taking into account all possible collisional and radiative processes of atoms and ions in plasma. We have carried out OES and CRM for CCP and ICP systems and the spectroscopic results for Ar plasma depending on gas pressure, applied rf power, and electron temperature/density are presented and analyzed. The electron temperature and density determined by our OES and CRM have been compared with those by a Langmuir probe. The sensitivity of the CRM to the underlying atomic data, optical trapping, and electron energy distribution function is discussed in detail. 

PP11.00115: Implementation of Optical Emission Diagnostics for EEDFs on a Helicon Plasma Jessica L Pachicano, John B Boffard, Chun C Lin, Amy E Wendt Optical emission spectroscopy (OES) is attractive as a noninvasive approach for measuring electron energy distribution functions (EEDF) in lowtemperature plasmas. Adaptation of an approach successfully developed and implemented on an argon inductivelycoupled plasma (ICP) to a helicon plasma system is the focus of this study. Trial EEDFs are an input to model calculations of excitation rates for select electronic transitions using known collision cross sections, and yielding the system EEDF as the trial that results in a best match to a set of measured emission intensities. Preliminary helicon OES data show regimes with much stronger argon ion emissions than observed in the ICP, where argon ion lines were so weak that they could not be productively included along with neutral lines in the OES analysis. Because of the high threshold energy for excitation of argon ion emissions, they signify the presence of energetic electrons, providing an opportunity to extend testing of the diagnostic to a new regime. Potential for improvements in the OES diagnostic for plasmas with a significant population of relatively high energy electrons, through the addition of argon ion lines to the emission model, will also be discussed. 

PP11.00116: Kinetic Simulations of High Power Impulse Magnetron Sputtering Process Ihor Holod, Anthony J. Link, Andrea Elizabeth Schmidt, Dale R Welch, David V Rose, Dustin Offermann HiPIMS is the magnetron sputtering regime which utilizes short high voltage pulses of tens of microseconds, as an alternative to the DC operation regime. HiPIMS is characterized by high density of plasma accumulated over the target, high energy of sputtered atoms, and a high ionization fraction of sputter products. Until now, optimization of magnetron devices has been done empirically or using reduced models. Reduced models, for example, may represent densities 10100x lower than actual experimental densities. We present fully kinetic 3D simulation of HiPIMS discharge using particleincell code Chicago from the developers of LSP [D. Welch, et.al, Phys. Plasmas 13, 063105 (2006)]. The model is validated with experimental measurements showing good agreement in terms of current and sputtering efficiency. Presented simulations capture the plasma formation, sputtering and transport of the sputtered material. 

PP11.00117: Kinetic and Fluid Simulations of Collisional Plasma Shock Samuel Jun Araki, Robert S Martin, David L Bilyeu Thermophysics Universal Research Framework (TURF) is an inhouse framework developed at the InSpace Propulsion Branch of the Air Force Research Laboratory (AFRL/RQRS). Cross verification between PIC, Vlasov, and fluid plasma models within the framework was conducted on the 1D electrostatic collisionless shock, and it was confirmed that the PIC and Vlasov models produced the same result while the fluid model did not capture the important kinetic features. This work will extend the previous work by including a collisional effect between charged species using Nanbu's method for the PIC model and solving the FokkerPlanck equation. The three models (PIC with Coulomb collision, VlasovFokkerPlanck, and fluid models) will be used to simulate a 1D collisional plasma shock within the same framework. 

PP11.00118: Numerical simulation of nonlinear behavior in plasma based photonic crystals and metamaterials using a multifluid plasma model W R Thomas, U Shumlak, F Righetti Plasma photonic crystals and metamaterials (PC/MMs) have the potential to significantly expand the capabilities of current microwave filtering and switching technologies by providing high speed (μs) control of energy bandgap/pass characteristics in the GHz through low THz range. While photonic crystals consisting of dielectric, semiconductor, and metallic matrices have been thoroughly investigated over the last several decades, plasmabased PC/MMs remain a relatively unexplored field. Numerical modeling efforts so far have largely used the standard methods of analysis for photonic crystals (the Plane Wave Expansion Method, Finite Difference Time Domain, and Drude model simulations), which do not capture nonlinear plasmaradiation interactions. In this study, a fully coupled Maxwell 5Nmoment multifluid plasma model is implemented within the WARPXM finite element code to investigate the nonlinear deformation of plasma structures under intense radiation. Transmission spectra of the deformed structures are compared with experimental data and ANSYS HFSS calculations. It is proposed that observed bandgap broadening could be harnessed for plasmabased adjustable power modulators. 

PP11.00119: Generation of DeuteriumRich Plasma by a Pulsed Vacuum Arc with Scandium Deuteride Film Cathode Tao Wang, Le Zhen, Pan Dong, Zhen Yang, Jidong Long Vacuum arc discharges provide simple and efficient methods for plasma formation. The cathode material is vaporized and ionized at cathode spotstiny plasma sites of very high current density. Plasma rich in hydrogen ions, especially for pulse, intense current hydrogen ion, are of interest for a wild range of plasma technologies, e.g., for the neutron generators. This paper reports on a study of the properties of the plasma produced in a vacuum arc discharge with scandium deuteride thin film cathode. It was shown that the electron temperature was about 3ev to 5.5ev, the electron density of 5.5×10^{12}cm^{2} to 9.5×10^{12}cm^{12} within 80A to 120A arc current and 5us pulse duration. The ion masstocharge spectrum of the plasma was investigated by magnetic mass spectrometry. For all arc parameters considered, there is one arc parameter for plasma most rich in hydrogen ions. This is determined by the structure of the discharge channel and the cathode material. After plasma diffusion, we found that the various ion components have different spatial distributions due to the initial momentum distribution and Ion stiffness. This will help us continue to increase the purity of deuterium ions in pulsed vacuum arc discharge. 

PP11.00120: Langmuir Probe Measurement Approach for Capturing the Electron Drift Velocity in a Halleffect Thruster Kimberly R Trent, Alec D Gallimore, John E Foster Langmuir probes (LP) are used to obtain electron temperature, density, and electron velocity distribution function (EVDF) in the plumes of Halleffect Thrusters (HETs). Confounding straightforward implementation of the EVDF measurement and subsequent analysis of IV traces from cylindrical probes is the flowing plasma. The usual simplifying assumption is that the EVDF is Maxwellian, which requires the probes to be aligned with the flow. There is evidence to suggest that the electrons are actually nonMaxwellian. In this regard, it’s critical to measure EVDF without simplifying assumptions. The true energetics of the electrons may yield a great deal of insight into the socalled anomalous electron diffusion problem in Hall thrusters. Here, we present an approach to obtaining the EVDF where the probe’s axis is oriented perpendicular to the plasma flow. The resulting characterization of the EVDF revealed that the distribution is best described by a drifting Maxwellian. The implications of the drift velocity value are discussed. 
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