Bulletin of the American Physical Society
59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017; Milwaukee, Wisconsin
Session GP11: Poster Session III: Reconnection; Laserplasma Interactions and Acceleration; Plasma Technology; DIIID I; Hohlraum and XRay Cavity Physics; Computation 
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Room: Exhibit Hall D 

GP11.00001: RECONNECTION 

GP11.00002: Hard Xray Bursts Observed in Association with Magnetic Reconnection in a SolarRelevant Lab Experiment Ryan S. Marshall, Paul M. Bellan Measurements by a plastic scintillator show transient emission of a submicrosecond pulse of 6 keV Xrays by a cold, dense MHDdriven plasma jet having a collision mean free path much shorter than the jet dimensions so that acceleration of any particles to high energy was not expected. The Xray pulse occurs when the jet undergoes a kink instability which accelerates the jet laterally so that a fastgrowing secondary RayleighTaylor instability is triggered that then breaks the jet. It is proposed that despite the short collision mean free path, an inductive electric field associated with this breaking accelerates a certain subgroup of electrons to 6 keV energy without any of these electrons undergoing collisions. It is further proposed that after being accelerated to high energy, the fast electrons are suddenly decelerated via collisions and radiate Xrays. Extrapolation to both the solar corona and chromosphere predicts the acceleration of a small subset of electrons to very large superthermal energies by subDreicer electric fields. [Preview Abstract] 

GP11.00003: Effective Ion Heating in Guide Field Reconnection Xuehan Guo, Ritoku Horiuchi, Shunsuke Usami, Yasushi Ono The energy conversion mechanism for ion perpendicular thermal energy is investigated by means of twodimensional, full particle simulations in an open system. It is shown that ions gain kinetic energy due to the plasma potential drop, which is caused by the charge separation in the one pair of separatrix arms. Based on the force balance in the inflow direction, the strength of the normalized charge density can be expressed by electron Alfv\'{e}n velocity, which is measurable value in the laboratory experiment and/or satellite observation. Meanwhile, we found that the accelerated ions form a ring shape like distribution in $f(v_{1},v_{2})$, as a result, the ion perpendicular temperature $T_{i,perp}$ increases from inflow region. Here, both $v_{1}$ and $v_{2}$ are perpendicular to the magnetic field and $v_{2}$ is parallel to the inplane. The mixing of particle populations is verified by means of tracing ions and it is shown three typical particle orbits and each orbit has different entry angle to the potential drop. This ring shape like distribution consists three different population due to the difference of the entry angles to the potential drop. This mixing process will thermalize ions and produce entropy without collisions. [Preview Abstract] 

GP11.00004: Plasma Transport at the Magnetopause in 3D Kinetic Simulations of MMS Reconnection Site Encounters with Varying Guide Fields Ari Le, William Daughton, Obioma Ohia, LiJen Chen, YiHsin Liu We present 3D fully kinetic simulations of asymmetric reconnection with plasma parameters matching MMS magnetopause diffusion region crossings with varying guide fields of $\sim$0.1 \footnote{Burch et al., Science (2016)}, $\sim$0.4 \footnote{Chen et al. JGR (2017)}, and $\sim$1 \footnote{Burch and Phan, GRL (2016)} of the reconnecting sheath field. For the weakest guide field case, drift turbulence at the magnetospheric separatrix was found to enhance transport and parallel electron heating \footnote{Le et al., GRL (2017)}. Here, we study how varying magnetic shear affects the morphology and plasma transport of the reconnecting magnetopause current sheet. Reconnection rates in 2D and 3D are compared using diagnostics based on particle mixing and on the magnetic field lineintegrated parallel electric field. The role of magnetic shear in altering energization and particle distributions along the turbulent magneospheric separatrix is also studied. The PIC simulation results are compared to MMS observations. [Preview Abstract] 

GP11.00005: Time domain structures in a colliding magnetic flux rope experiment Shawn Wenjie Tang, Walter Gekelman, Timothy DeHaas, Steve Vincena, Patrick Pribyl Electron phasespace holes, regions of positive potential on the scale of the Debye length, have been observed in auroras as well as in laboratory experiments. These potential structures, also known as Time Domain Structures (TDS), are packets of intense electric field spikes that have significant components parallel to the local magnetic field. In an ongoing investigation at UCLA, TDS were observed on the surface of two magnetized flux ropes produced within the Large Plasma Device (LAPD). A barium oxide (BaO) cathode was used to produce an 18~m long magnetized plasma column and a lanthanum hexaboride (LaB$_6$) source was used to create 11~m long kink unstable flux ropes. Using two probes capable of measuring the local electric and magnetic fields, correlation analysis was performed on tens of thousands of these structures and their propagation velocities, probability distribution function and spatial distribution were determined. The TDS became abundant as the flux ropes collided and appear to emanate from the reconnection region in between them. In addition, a preliminary analysis of the permutation entropy and statistical complexity of the data suggests that the TDS signals may be chaotic in nature. [Preview Abstract] 

GP11.00006: Secondary Instabilities in 3D Magnetic Reconnection under a Strong Guide Field Xueyi Wang, Yu Lin, Liu Chen 3D magnetic reconnection is investigated using the gyrokinetic electron and fullykinetic ion (GeFi) particle simulation model. The simulation is carried out for a force free current sheet with a strong guide field $B_G$ as occurring in solar and laboratory plasmas. It is found that secondary instabilities are excited in the separatrix region of the primary reconnection due to the 3D effects associated with the finite $k_z$, where $k_z$ is the wave number along the guide field direction. The instabilities are demonstrated as being of the MHD kink type, which lead to electron heating and acceleration in the parallel direction. The dependence of the growth rate of the secondary instabilities on the electronion resistivity, the iontoelectron mass ratio $m_i/m_e$, and the halfwidth of the current sheet are also investigated. [Preview Abstract] 

GP11.00007: Understanding the dynamics and the energetics of magnetic reconnection in laboratory and space plasmas Masaaki Yamada, Jongsoo Yoo, Hantao Ji, Jon JaraAlmote, Will Fox, Russell Kulsrud We will present recent findings in the research of asymmetric and symmetric magnetic reconnection both in laboratory and space plasmas [1]. In spite of the huge difference ($10^6$$10^7$) in physical scales, we find remarkable commonality between the properties and the dynamics of the reconnection layer in laboratory and space plasmas. The recent significant progress in diagnostics in the both fields made us possible to directly compare the observed physics processes. The experimental results on the energy conversion and partitioning are discussed and compared with quantitative estimates based on twofluid analysis as well as space observations. We observed notable similarity in the energy partitioning in the reconnection layer of the MRX and space observations [1,2]. Furthermore, we have observed whistler waves and lowerhybrid frequency fluctuations at the lower density side of asymmetric reconnection layer on MRX [2]. The experimental results are remarkably consistent with the recent space observations from MMS [3]. We directly compare the data from the MRX and the recent MMS observations which show very similar power spectra. Ref.: [1] M. Yamada, et al, PoP 23, 055402 (2016), [2] J. Yoo et al, Submitted to J. G.R. (2017), [3] L. J. Chen et al, This conf. [Preview Abstract] 

GP11.00008: Studies of waves during asymmetric reconnection in laboratory and space Jongsoo Yoo, Evan Yerger, Jonathan JaraAlmonte, Masaaki Yamada, Hantao Ji, Will Fox, LiJen Chen Wave activities during asymmetric reconnection have been studied by directly comparing data from the Magnetic Reconnection Experiment (MRX) with data from the Magnetospheric Multiscale (MMS). The power spectrum near separatrices on the lowdensity (magnetosphere) side shows remarkable similarities. Regarding fluctuations driven by lower hybrid drift instabilities (LHDI), it shows broad spectrum with the energy concentrated mostly below the lowerhybrid frequency. The free energy source of LHDI is the diamagnetic current by the strong density gradient near the separatrix region. The whistler waves show a power spectrum concentrated around half of the electron cyclotron frequency ($0.5f_{ce}$). In MMS, they propagate mostly parallel to the field line toward the Xline with a relatively high phase velocity ($\sim5\times10^7$ m/s). The whistler waves are also observed in the exhaust region and near the electron diffusion region (EDR). However, they become intermittent and with the frequency higher than $0.5f_{ce}$ in the exhaust region and higher than $0.5f_{ce}$ near the EDR. The dominant wave vector satisfies $kd_e\sim1$ for all cases. Possible excitation mechanisms for the observed whistler waves are discussed. [Preview Abstract] 

GP11.00009: Drift Kinetic Measurements of Plasma Gradients in MMS Data Blake Wetherton, Jan Egedal, Peter Montag, Ari Le, William Daughton, Benoit Lavraud In magnetic reconnection, magnetic stress energy is converted into particle energy through the topological rearrangement of magnetic field lines allowed by the breakdown of ideal MHD on small spatial scales. While many models exist to explain reconnection, the crucial physics lies in a thin current layer $\sim 1$ $d_e$ wide. NASA's Magnetospheric Multiscale (MMS) mission seeks to directly investigate magnetic reconnection in Earth's magnetosphere with a tetrahedral formation of four spacecraft. While gradients in plasma properties can be estimated through spacecraft positions, the spacing between each tends to be $\sim 10$ $d_e$, causing gradients at the crucial scale to be poorly resolved. We present a driftkinetic method for obtaining gradients in the plasma distribution function with data from a single spacecraft. This model is derived from drift kinetics, verified with a VPIC fullykinetic simulation, and applied to MMS data to infer the geometry of the reconnection region and demonstrate gradientscale resolution superior to finite difference methods between the four spacecraft. [Preview Abstract] 

GP11.00010: Observation of Characteristic Reconnection Regime Structures in the Terrestrial Reconnection Experiment (TREX) Samuel Greess, Jan Egedal, Joseph Olson, Alexander MilletAyala, Rachel Myers, John Wallace, Michael Clark, Cary Forest Different regimes of collisionless asymmetric reconnection have different characteristic features and are accessed by varying the plasma parameters of the system [1]. Recently, the Terrestrial Reconnection Experiment (TREX), part of the Wisconsin Plasma Astrophysics Laboratory (WiPAL), used four coils in a 3m spherical vacuum vessel filled with plasma to drive reconnection with an external Helmholtz field. By varying the Helmholtz field, drive field, and plasma species, TREX entered experimentally unexplored reconnection regimes. Using magnetic probes, we observed the characteristic structures of these regimes, including exhaust jets and current layers with widths of only a few d$_{\mathrm{e}}$. These results show better agreement with kinetic simulation than had previously been reported [2] [3]. [1] Le, A. et al. Phys. Rev. Lett., 110, 135004. doi:10.1103/PhysRevLett.110.135004. [2] Le, A. et al. Geophys. Res. Lett., 44, 20962104. doi:10.1002/2017GL072522. [3] Ji, H. et al. Geophys. Res. Lett., 35, L13106. doi:10.1029/2008GL034538. [Preview Abstract] 

GP11.00011: Plasmoid Instability in Evolving Current Sheets and Onset of Fast Reconnection YiMin Huang, Luca Comisso, Amitava Bhattacharjee A proper description for the onset of the plasmoid instability must incorporate the evolving process of the current sheet, as a high Lundquist number current sheet usually breaks apart before it approaches the SweetParker width. We carry out twodimensional simulations and theoretical analysis of the plasmoid instability in an evolving background. The plasmoid instability disrupts the current sheet and enters nonlinear regime when the sizes of plasmoids become comparable to the inner layer width of the tearing mode. The linear growth rate, current sheet width, and dominant wavenumber at current sheet disruption depend on not only the Lundquist number, but also the initial noise amplitude. The scalings obtained from simulations can be reproduced with a phenomenological model, which incorporates the effects of linear growth and advective losses due reconnection outflow. Our model predicts a critical Lundquist number below which disruption does not occur. The critical Lundquist number is not a constant value but has a weak dependence on the noise amplitude. [Preview Abstract] 

GP11.00012: 3D magnetic reconnection studies in the Terrestrial Reconnection Experiment (TREX) Alexander MilletAyala, Jan Egedal, Joseph Olson, Samuel Greess, Rachel Myers, John Wallace, Michael Clark, Cary Forest Recent experimental studies on the Terrestrial Reconnection Experiment (TREX) focus on nominally 2D asymmetric magnetic reconnection configurations. In 3D reconnection, however, regions of zero magnetic fields, called magnetic nulls, become important sites of potential particle acceleration. In order to study 3D nullpoint reconnection in TREX, an adjustable pulsed coil (null coil) is added to the experiment to introduce magnetic nulls. Tilting the null coil relative to the existing reconnection drive and Helmholtz coils forms complex 3D magnetic field geometries, vastly different from other 2D reconnection geometries explored on TREX. To measure the effects of the added nullpoints, a combination of magnetic probes and Langmuir probes are used to characterize the plasma. [Preview Abstract] 

GP11.00013: Endogenous Magnetic Reconnection and Associated High Energy Plasma Processes B. Coppi, B. Basu The existence of an endogenous magnetic reconnection process in weakly collisional plasmas is proposed that relies on the presence of a significant electron temperature gradient [1] and a local current density gradient within the region where a drastic change of magnetic field topology is produced. The newly identified mode involves widths of the layer in which reconnection takes place that remain relevant even when large macroscopic distances are considered, such as those of interest to space and astrophysics. Given that plasmas in the Universe with considerable electron thermal energy contents are ubiquitous, it makes sense to rely on this process to generate, through magnetic field reconnection, high energy particle populations [1], momentum and angular momentum transport and, in any case, new magnetic field configurations. A depletion of magnetic energy is associated with a suppression of the current density gradient.\\ [1] B. Coppi, B. Basu and A. Fletcher, $\il{Nucl. Fusion}$, $\bf{57}$, 7 (2017). [Preview Abstract] 

GP11.00014: Fluxrope distribution function through a Maximum Entropy principle Manasvi Lingam, Luca Comisso, Amitava Bhattacharjee The Principle of Maximum Entropy (MaxEnt) is utilized for inferring the distribution function of flux ropes formed through a resistive instability as a function of their mass, flux and velocity [1]. Our treatment is 3D (flux ropes) in nature, as opposed to previous works that have studied 2D structures (plasmoids) [2,3]. The distributions for the mass, width, flux and helicity are characterized by a powerlaw behavior with exponents of 4/3, 2, 3 and 2 respectively for small values, and display an exponential falloff for large values. The velocity distribution is shown to be flat at small values and becomes a power law for large values with an exponent of 7/3. A preliminary comparison with observational evidence suggests that the predictions of the theoretical model are consistent with the latter.\\ References: [1] M. Lingam, L. Comisso & A. Bhattacharjee, arXiv:1702.05782 (2017) [2] D. A. Uzdensky, N. F. Loureiro & A. A. Schekochihin, Phys. Rev. Lett., 105, 235002 (2010) [3] Y.M. Huang & A. Bhattacharjee, Phys. Rev. Lett., 109, 265002 (2012) [Preview Abstract] 

GP11.00015: Survey of Waves in the Ion Diffusion Region of Asymmetric Reconnection in the Dayside Magnetopause Evan Yerger, Jongsoo Yoo, LiJen Chen, EunHwa Kim, Masaaki Yamada, Hantao Ji, Will Fox Wave modes in the ion diffusion region of an active dayside reconnection site are characterized using high timeresolution data from NASA's Magnetospheric Multiscale (MMS) mission. We observe highamplitude, lowfrequency ($\leq \omega_{LH}$) electrostatic fluctuations near the magnetosphericside separatrices, which are most likely a result of the lower hybrid drift instability (LHDI). In the magnetospheric upstream region we find whistler waves with $\omega\approx \Omega_e/2$ and phase velocity near $5\times 10^7\hspace{2pt}m/s$ propagating toward the Xline. In the exhaust region we find a largely different set of electromagnetic waves, including an obliquelypropagating, highfrequency ($\omega>\omega_{LH}$), lefthandpolarized waves with phase velocities around $1\times 10^6\hspace{2pt}m/s$. Possible relationships between these waves and local distribution functions will be investigated through analysis of data from the fast plasma instrument (FPI). We will also discuss the possibility of mode conversion from electrostatic lower hybrid waves to the electromagnetic waves we observe. [Preview Abstract] 

GP11.00016: FLARE: A New User Facility for Studies of MultipleScale Physics of Magnetic Reconnection and Related Phenomena Through \textbf{\textit{insitu}} Measurements Hantao Ji, A. Bhattacharjee, A. Goodman, S. Prager, W. Daughton, R. Cutler, W. Fox, F. Hoffmann, M. Kalish, T. Kozub, J. JaraAlmonte, C. Myers, Y. Ren, P. Sloboda, M. Yamada, J. Yoo, S.D. Bale, T. Carter, S. Dorfman, J. Drake, J. Egedal, J. Sarff, J. Wallace The FLARE device (Facility for Laboratory Reconnection Experiments; flare.pppl.gov) is a new laboratory experiment under construction at Princeton for the studies of magnetic reconnection in the multiple Xline regimes directly relevant to space, solar, astrophysical, and fusion plasmas, as guided by a reconnection phase diagram [Ji \& Daughton (2011)]. The whole device have been assembled with first plasmas expected in the fall of 2017. The main diagnostics is an extensive set of magnetic probe arrays, currently under construction, to cover multiple scales from local electron scales ($\sim$2 mm), to intermediate ion scales ($\sim$10 cm), and global MHD scales ($\sim$1 m), simultaneously providing {\it insitu} measurements over all these relevant scales. The planned procedures and example topics as a user facility will be discussed. [Preview Abstract] 

GP11.00017: Onset of magnetic reconnection in a weakly collisional, high$\beta$ plasma Andrew Alt, Matthew Kunz In a magnetized, weakly collisional plasma, the magnetic moment of the constituent particles is an adiabatic invariant. An increase of the magneticfield strength in such a plasma thus leads to an increase in the thermal pressure perpendicular to the field lines. Above a $\beta$dependent threshold, this pressure anisotropy drives the mirror instability, which produces strong distortions in the field lines and traps particles on ionLarmor scales. The impact of this instability on magnetic reconnection is investigated using simple analytical and numerical models for the formation of a current sheet and the associated production of pressure anisotropy. The difficulty in maintaining an isotropic, Maxwellian particle distribution during the formation and subsequent thinning of a current sheet in a weakly collisional plasma, coupled with the low threshold for the mirror instability in a high$\beta$ plasma, imply that the topology of reconnecting magnetic fields can radically differ from the standard Harrissheet profile often used in kinetic simulations of collisionless reconnection. Depending on the rate of currentsheet formation, this mirrorinduced disruption may occur before standard tearing modes are able to develop. [Preview Abstract] 

GP11.00018: Experimental Investigation of Magnetic Reconnection in Weakly Ionized Plasmas Jonathan JaraAlmonte, Hantao Ji, Jongsoo Yoo, Masaaki Yamada, Will Fox Magnetic reconnection is a fundamental process in magnetized plasmas wherein stored magnetic energy is rapidly released. While commonly studied in fully ionized plasmas, many important systems (e.g., the chromosphere or interstellar medium) are weakly ionized, which can significantly modify reconnection physics. Recent IRIS observations have enabled detailed studies of chromospheric reconnection, highlighting its in partially ionized systems [1]. Previous experiments on the Magnetic Reconnection Experiment have qualitatively shown that reconnection is slow in partially ionized systems, in contrast to theoretical predictions, although the underlying physics is unclear [2]. Here, new experiments are performed to examine the detailed role of neutrals. An insitu filterscope has been developed to simultaneously measure Helium line emission at 668, 706, and 728 nm from a localized, 1 cm$^3$ volume with high timeresolution. Collisional radiative modeling is used to determine the neutral density, as well as the electron density and temperature. By measuring the neutral density, the detailed neutralplasma coupling during reconnection is studied in detail. [1] De Pontieu, Bart, et al. Solar Physics 289.7 (2014) [2] Lawrence, Eric E., et al. Physical review letters 110.1 (2013) [Preview Abstract] 

GP11.00019: Electron phase space structure of asymmetric reconnecting current sheets with varying guide fields Obioma Ohia, Ari Le, William Daughton Magnetic reconnection in asymmetric current sheets is known to produce highly structured electron velocity distributions, including crescents within the diffusion region [Bessho et al., GRL 2016] and crescents and mixed populations along the separatrices [Egedal et al., PRL (2016), Hesse et al., PRL (2017)]. Using a series of 2D particleincell simulations of asymmetric magnetic reconnection with varying guide magnetic fields, we investigate electron distribution functions in both the upstream and exhaust regions of reconnecting current sheets. Electric fields, especially those parallel to the local magnetic field, play an important role in shaping and producing beams in velocity space. We relate the electron distributions to macroscopic field and plasma structures and compare our PIC results to recent Magnetospheric Multiscale (MMS) Mission measurements during dayside magnetopause reconnection. [Preview Abstract] 

GP11.00020: How Alfv\'en waves set the large scale structure of magnetic reconnection. Harsha Gurram, Jan Egedal A PIC simulation of antiparallel reconnection shows the formation of the outofplane or Hall magnetic field that extends hundreds of inertial lengths from the Xline.This structure is generated by fieldaligned electron currents that flow outside the magnetic separatrices when ion and electrons decouple on length scales less than $d_{i}$. We observe that this Hall field propagates from the Xpoint to far downstream into the exhaust along the magnetic field lines at Alfv\'enic speed.Thus the propagation of this large scale reconnection structure can be associated with a Alfv\'en wave generated in the inner electron diffusion region, specifically near the Xline. [Preview Abstract] 

GP11.00021: Kubo Resistivity of magnetic flux ropes Walter Gekelman, Tim DeHaas, Pat Pribyl, Stephen Vincena, Bart Van Compernolle, Rick Sydora, Shawn Wenjie Tang Magnetic flux ropes are bundles of twisted magnetic fields and their associated current. They are common on the surface of the sun (and presumably all other stars) and are observed to have a large range of sizes and lifetimes. They can become unstable and resulting in coronal mass ejections that can travel to earth and indeed, have been observed by satellites. Two side by side flux ropes are generated in the LAPD device at UCLA. Using a series of novel diagnostics the following key quantities, \textbf{B,} \textbf{u}, Vp, n, Te have been measured at more than 48,000 spatial locations and 7,000 time steps. Every term in Ohm's law is also evaluated across and along the local magnetic field and the plasma resistivity derived and it is shown that Ohms law is nonlocal. The electron distribution function parallel and antiparallel to the background magnetic field was measured and found to be a drifting Kappa function. The Kubo AC conductivity at the flux rope rotation frequency, a 3X3 tensor, was evaluated using velocity correlations and will be presented. This yields meaningful results for the global resistivity. Frequency spectra and the presence of time domain structures may offer a clue to the enhanced resistivity. [Preview Abstract] 

GP11.00022: Pressure Anisotropy Measurements on the Terrestrial Reconnection Experiment Rachel Myers, Jan Egedal, Joseph Olson, Samuel Greess, Alexander MilletAyala, Michael Clark, Paul Nonn, John Wallace, Cary Forest The Terrestrial Reconnection Experiment (TREX) at the Wisconsin Plasma Astrophysics Laboratory (WiPAL) studies collisionless magnetic reconnection. In this regime, electron pressure anisotropy should develop, deviating from Hall reconnection dynamics and driving largescale current layer formation [1]. A multitip version of the Mprobe of Shadman [2], containing 32 Langmuir probe tips and two magnetic coils, measures this anisotropy. Each tip is biased to a different potential, simultaneously measuring discrete parts of the IV characteristic. Pulsing the coil locally increases the magnetic field near the tips, inducing a magnetic mirror force to reflect electrons with large values of $v_{\perp}/v$. The change in velocity modifies the IV characteristic and can be used to infer $p_{\parallel}/p_{\perp}$. Results and analysis from the probe are presented. [1] J. Egedal \emph{et al.}, Nature Phys. (2012). [2] K. Shadman, Phys. Plasmas (2004). [Preview Abstract] 

GP11.00023: Overview and first results of experiments on magnetic reconnection between colliding magnetized plasmas at the National Ignition Facility W. Fox, M. Rosenberg, D. Schaeffer, G. Fiksel, H.S. Park, D. Kalantar, A. Bhattacharjee, Y.M. Huang, H. Ji, J. Matteucci, L. Gao, D. Uzdensky, A. Birkel, C.K. Li, S.X. Hu, A. Shvydky Expanding laserproduced plasmas naturally selfgenerate magnetic fields by the Biermann battery effect, and the collision of two plumes can drive magnetic reconnection. The National Ignition Facility at LLNL occupies a unique position for laserdriven magnetic reconnection experiments by simultaneously allowing very large plasma temperature, low plasma resistivity, and large system size, which allows observation of secondary instabilities driven during magnetic reconnection and particle acceleration relevant to astrophysical plasmas. Magnetic reconnection experiments have been conducted on the NIF through the NIF Discovery Science program with the first experimental shots conducted in May 2017. We will present the design of the experimental platform and results from the first experimental day. Magnetic reconnection data is obtained from proton radiography based on a DHe3 backlighter, xray selfemission, and a new lowenergy particle spectrometer (NIF EPPS300G) developed by the NIF Facility and Engineering and fielded for the first time on these experiments. [Preview Abstract] 

GP11.00024: The kinetic structure of the electron diffusion region observed by MMS during asymmetric reconnection Egedal Jan, Blake Wetherton, Ari Le, William Daughton During asymmetric magnetic reconnection in the dayside magnetopause in situ spacecraft measurements by NASA's MMS mission provide new detailed information on the electron dynamics within the electron diffusion region. In particular, we report here on observations by MMS4 which traveled the closest on the topological Xline [1] in the event on October 16, 2015, first reported by Burch et al., [2]. In addition to crescent shaped electron distributions [2,3], the measurements include electron beams flowing in toward the diffusion region. These beams of incoming electrons are formed by $E_{\parallel}$ acceleration along the highdensity side separatrices. They penetrate across the electron diffusion region, where their directions are nearly unaffected by the rapid changes in the magnetic field geometry. Matching electron beam features are observed in 2.5D kinetic simulations, revealing their role in breaking the electron frozeninlaw through contributions to the offdiagonal stress in the electron pressure tensor.\\[1ex] [1] Denton et al., Geophys.~Res.~Lett., 43, 5589–5596, (2016).\\[1ex] [2] Burch et al., Science 352, 2939, (2016).\\[1ex] [3] Egedal et al., PRL 117, 185101 (2016).\\[1ex] [Preview Abstract] 

GP11.00025: Impact of compressibility and a guide field on Fermi acceleration during magnetic island coalescence Peter Montag, Jan Egedal, Emily Lichko, Blake Wetherton Previous work has shown that Fermi acceleration can be an effective heating mechanism during magnetic island coalescence, where electrons may undergo repeated reflections as the magnetic field lines contract. This energization has the potential to account for the powerlaw distributions of particle energy inferred from observations of solar flares. Here, we develop a generalized framework for the analysis of Fermi acceleration that can incorporate the effects of compressibility and nonuniformity along field lines, which have commonly been neglected in previous treatments of the problem. Applying this framework to the simplified case of the uniform flux tube allows us to find both the powerlaw scaling of the distribution function and the rate at which the powerlaw behavior develops. We find that a guide magnetic field of order unity effectively suppresses the development of powerlaw distributions. [Preview Abstract] 

GP11.00026: LASERPLASMA INTERACTIONS AND ACCELERATION 

GP11.00027: Deployment of the OSIRIS EMPIC code on the Intel Knights Landing architecture Ricardo Fonseca Electromagnetic particleincell (EMPIC) codes such as OSIRIS [1] have found widespread use in modelling the highly nonlinear and kinetic processes that occur in several relevant plasma physics scenarios, ranging from astrophysical settings to highintensity laser plasma interaction.~Being computationally intensive, these codes require large scale HPC systems, and a continuous effort in adapting the algorithm to new hardware and computing paradigms. In this work, we report on our efforts on deploying the OSIRIS code on the new Intel Knights Landing (KNL) architecture. Unlike the previous generation (Knights Corner), these boards are standalone systems, and introduce several new features, include the new AVX512 instructions and onpackage MCDRAM. We will focus on the parallelization and vectorization strategies followed, as well as memory management, and present a detailed performance evaluation of code performance in comparison with the CPU code. [1] R. A. Fonseca et al., Lecture Notes in Computer Science \textbf{2331}, 342351 (2002) [Preview Abstract] 

GP11.00028: Endtoend plasma bubble PIC simulations on GPUs Kai Germaschewski, William Fox, Jackson Matteucci, Amitava Bhattacharjee Accelerator technologies play a crucial role in eventually achieving exascale computing capabilities. The current and upcoming leadership machines at ORNL (Titan and Summit) employ Nvidia GPUs, which provide vast computational power but also need specifically adapted computational kernels to fully exploit them. In this work, we will show endtoend particleincell simulations of the formation, evolution and coalescence of lasergenerated plasma bubbles. This work showcases the GPU capabilities of the PSC particleincell code, which has been adapted for this problem to support particle injection, a heating operator and a collision operator on GPUs. [Preview Abstract] 

GP11.00029: Simulating The Prompt Electromagnetic Pulse In 3D Using Vector Spherical Harmonics Alex Friedman, Bruce I. Cohen, Chester D. Eng, William A. Farmer, David P. Grote, Hans W. Kruger, David J. Larson We describe a new, efficient code for simulating the prompt electromagnetic pulse. In SHEMP ("Spherical Harmonic EMP"), we extend to 3D the methods pioneered in C. Longmire's CHAP code [1]. The geomagnetic field and air density are consistent with CHAP's assumed spherical symmetry only for narrow domains of influence about the line of sight, limiting validity to very early times. Also, we seek to model inherently 3D situations. In CHAP and our own CHAPlite [2], the independent coordinates are r (the distance from the source) and $\tau =$ tr/c; the pulse varies slowly with r at fixed $\tau $, so a coarse radial grid suffices. We add nonsphericallysymmetric physics via a vector spherical harmonic decomposition. For each (l,m) harmonic, the radial equation is similar to that in CHAP and CHAPlite. We present our methodology [3] and results on model problems. [1] C. L. Longmire, IEEE Trans. Electromag. Compatibility 20 no. 1, 3 (1978). [2] W. A. Farmer, et al., IEEE Trans. Nucl. Sci. 63, 1259 (2016). [3] A. Friedman, et al., submitted to J. Rad. Effects Research and Engr.; also report LLNLJRNL732043 (2017). [Preview Abstract] 

GP11.00030: Reduced 3d modeling on injection schemes for laser wakefield acceleration at plasma scale lengths Anton Helm, Jorge Vieira, Luis Silva, Ricardo Fonseca Current modelling techniques for laser wakefield acceleration (LWFA) are based on particleincell (PIC) codes which are computationally demanding. In PIC simulations the laser wavelength $\lambda_0$, in $\mu$mrange, has to be resolved over the acceleration lengths in meterrange. A promising approach is the ponderomotive guiding center solver (PGC)~[1, 2] by only considering the laser envelope for laser pulse propagation. Therefore only the plasma skin depth $\lambda_p$ has to be resolved, leading to speedups of $(\lambda_p/\lambda_0)^2$. This allows to perform a widerange of parameter studies and use it for $\lambda_0 \ll \lambda_p$ studies. We present the 3d version of a PGC solver in the massively parallel, fully relativistic PIC code OSIRIS~[3]. Further, a discussion and characterization of the validity of the PGC solver for injection schemes on the plasma scale lengths, such as downramp injection, magnetic injection~[4] and ionization injection, through parametric studies, full PIC simulations and theoretical scaling, is presented. References: [1] D. Gordon et. al., IEEE Trans. Plasma Sci. 28, 1135 (2000) [2] A. Helm et. al., submitted (2017) [3] R. A. Fonseca et. al., Lect. Notes Comp. Sci., 2331, 343 (2002) [4] J. Vieira et al., Phys. Rev. Lett. 106, 225001 (2011) [Preview Abstract] 

GP11.00031: Convergence of the Ponderomotive Guiding Center approximation in the LWFA Thales Silva, Jorge Vieira, Anton Helm, Ricardo Fonseca, Luis Silva Plasma accelerators arose as potential candidates for future accelerator technology in the last few decades because of its predicted compactness and low cost. One of the proposed designs for plasma accelerators is based on Laser Wakefield Acceleration (LWFA). However, simulations performed for such systems have to solve the laser wavelength which is orders of magnitude lower than the plasma wavelength. In this context, the Ponderomotive Guiding Center (PGC) algorithm for particleincell (PIC) simulations is a potent tool. The laser is approximated by its envelope which leads to a speedup of around 100 times because the laser wavelength is not solved. The plasma response is well understood, and comparison with the full PIC code show an excellent agreement. However, for LWFA, the convergence of the selfinjected beam parameters, such as energy and charge, was not studied before and has vital importance for the use of the algorithm in predicting the beam parameters. Our goal is to do a thorough investigation of the stability and convergence of the algorithm in situations of experimental relevance for LWFA. To this end, we perform simulations using the PGC algorithm implemented in the PIC code OSIRIS. To verify the PGC predictions, we compare the results with full PIC simulations. [Preview Abstract] 

GP11.00032: Twostage acceleration of externally injected electrons in plasma bubble derived from the combination of DLA and LWFA. Vladimir Khudik, Tianhong Wang, Daniel Vicuna, Xi Zhang, Gennady Shvets Simultaneous interactions of accelerated electrons directly with a laser pulse and with a laser wakefield are studied using a novel quasistatic 3D particleincell code. Relativistic electrons externally injected into the plasma bubble's decelerating phase can gain significant energy through the direct laser acceleration (DLA) mechanism from the driving laser pulse [13], increasing the amplitude of betatron oscillations. With time, the resonant interaction condition is violated, leading to gradual dephasing between electrons and laser wave, and to eventual slipping of the electrons to the back of the plasma bubble. After that, the oscillating electrons experience the second stage of acceleration gaining energy only from the bubble wakefield. We analyze each stage of acceleration and show that electrons undergoing two stages emits much more Xray radiation compared with those accelerated during one wakefield stage. This work was supported by DOE grant DESC0007889 and by AFOSR grant FA95501610013. [1] X. Zhang, V. N. Khudik and G. Shvets, Phys. Rev. Lett. 114, 184801 (2015). [2] X. Zhang, V. N. Khudik, A. Pukhov and G. Shvets, Plasma Phys. Control. Fusion 58 034011 (2016). [3] V. N. Khudik, X. Zhang and G. Shvets, arXiv: 1610.0945 (2015). [Preview Abstract] 

GP11.00033: Ultralow emittance electron beam generation using ionization injection in a plasma beatwave accelerator Carl Schroeder, Carlo Benedetti, Eric Esarey, Wim Leemans Ultralow emittance beams can be generated using ionization injection of electrons into a wakefield excited by a plasma beatwave accelerator. This alloptical method of electron beam generation uses three laser pulses of different colors. Two longwavelength laser pulses, with frequency difference equal to the plasma frequency, resonantly drive a plasma wave without fully ionizing a gas. A shortwavelength injection laser pulse (with a small ponderomotive force and large peak electric field), copropagating and delayed with respect to the beating longwavelength lasers, ionizes a fraction of the remaining bound electrons at a trapped wake phase, generating an electron beam that is accelerated in the wakefield. Using the beating of longwavelength pulses to generate the wakefield enables atomicallybound electrons to remain at low ionization potentials, reducing the required amplitude of the ionization pulse, and, hence, the initial transverse momentum and emittance of the injected electrons. An example is presented using two lines of a CO$_2$ laser to form a plasma beatwave accelerator to drive the wake and a frequencydoubled Ti:Al$_2$O$_3$ laser for ionization injection. [Preview Abstract] 

GP11.00034: Emittance preservation in plasmabased accelerators with ion motion Carlo Benedetti, Carl Schroeder, Eric E. Esarey, Wim Leemans In a plasmaacceleratorbased linear collider, the density of matched, lowemittance, highenergy particle bunches required for collider applications can be orders of magnitude above the background ion density, leading to ion motion, nonlinear focusing fields, and, hence, to beam emittance growth. By analyzing the response of the background ions to an ultrahigh density beam, analytical expressions, valid for nonrelativistic ion motion, are derived for the transverse wakefield and for the final (i.e., after saturation) bunch emittance. Analytical results are validated against numerical modeling. A class of initial beam distributions are derived that are equilibrium solutions, which require headtotail bunch shaping, enabling emittance preservation with ion motion. [Preview Abstract] 

GP11.00035: Plasma Channel Lenses and Plasma Tornadoes for Optical Beam Focusing and Transport R. F. Hubbard, D. Kaganovich, L. A. Johnson, D. F. Gordon, J. R. Penano, B. Hafizi, M. H. Helle, A. A. Mamonau Shaped plasmas offer the possibility of manipulating laser pulses at intensities far above the damage limits for conventional optics. An example is the plasma channel, which is a cylindrical plasma column with an onaxis density minimum. Long plasma channels have been widely used to guide intense laser pulses, particularly in laser wakefield accelerators. A new concept, the ``plasma tornado'', offers the possibility of creating long plasma channels with no nearby structures and at densities lower than can be achieved by capillary discharges. A short plasma channel can focus a laser pulse in much the same manner as a conventional lens or offaxis parabola. When placed in front of the focal point of an intense laser pulse, a plasma channel lens (PCL) can reduce the effective fnumber of conventional focusing optics. When placed beyond the focal point, it can act as a collimator. We will present experimental and modeling results for a new plasma tornado design, review experimental methods for generating short PCLs, and discuss potential applications. [Preview Abstract] 

GP11.00036: Filtering of higherorder laser modes using plasma structures Blagoje Djordjevic, Carlo Benedetti, Carl Schroeder, Eric Esarey, Wim Leemans Plasma structures based on leaky channels are proposed to filter higherorder laser mode content. The evolution and propagation of nonGaussian laser pulses in leaky channels is studied, and it is shown that, for appropriate laserplasma parameters, the higherorder laser mode content may be removed while the fundamental mode remains wellguided. The behavior of the multimode laser pulse is described analytically, including the derivation of the leakage coefficients, and compared to numerical calculations. Gaussian laser pulse propagation, without higherorder mode content, improves guiding in parabolic plasma channels, enabling extended interaction lengths for laserplasma accelerator applications. [Preview Abstract] 
(Author Not Attending)

GP11.00037: Spatial Control of Laser Wakefield Accelerated Electron Beams A. Maksimchuk, K. Behm, T. Zhao, A. S. Joglekar, A. Hussein, J. Nees, A. G. R. Thomas, K. Krushelnick, J. Elle, A. Lucero, G. M. Samarin, G. Sarry, J. Warwick 

GP11.00038: Abstract Withdrawn Plasmabased accelerators can generate about 1000 times stronger acceleration field compared with RFbased conventional accelerators, which can be done by high power laser and plasma. There are many issues in this research and one of them is development of a good plasma source for higher electron beam energy. For this purpose, we are investigating a special type of plasma source, which is a densitytapered gas cell with a mixedgas for easy injection. By this type of special gas cell, we expect higher electron beam energies with easy injection in the wakefield. In this poster, some experimental results for electron beam generation with the densitytapered mixedgas cell are presented. In addition to the experimental results, CFD (ComputationalFluidDynamics) and PIC (ParticleInCell) simulation results are also presented for comparison studies. 

GP11.00039: Wakefield simulation of solid state plasma Sahel Hakimi, Tam Nguyen, Deano Farinella, Calvin Lau, HsuanYu Wang, Peter Taborek, Toshiki Tajima Although it is known that the accelerating gradient of wakefield increases when laser frequency increases (i.e. critical density), there was no adequate technology to make intense Xray laser until recently. With the advent of the invention of Thin Film Compression, we now see the intense Xray laser technology that fits this need [1]. We have modified the EPOCH PIC code to include the lattice effect [2] of nanomaterials in our simulations. The present results indicate the accelerating gradient \(\sim0.3\frac{TeV}{cm}\) at the plasma density of \(10^{23} cm^{3}\) which agree well with the wakefield theory. This shows the concept of the solid state plasma wakefield in nanomaterials is validated by computation. This result is also consistent with previous findings [3], in which the lattice effect was neglected. [1] Tajima, T. (2014). Eur. Phys. J. \textbf{223}, 1037. [2] Tajima, T. {\&} Ushioda, S. (1978). Phys. Rev. B \textbf{18}, 1892. [3] Zhang, X. et al., (2016). Phys. Rev. Acc. Beams \textbf{19}, 101004. [Preview Abstract] 

GP11.00040: Relativistic Electron Acceleration by Surface Plasma Waves in the High Intensity Regime Xiaoming Zhu, Mirela Cerchez, Marco Swantusch, Bastian Aurand, Rajendra Prasad, Alexander Andreev, Oswald Willi High field plasmonics is one of the new research fields which has synergetically benefited from the advances in laser technology. The availability of radiation fields of intensities exceeding 10$^{\mathrm{18\thinspace }}$W/cm$^{\mathrm{2}}$ brought plasmonics into a new regime where relativistic and nonlinear effects start to dominate the dynamics of the surface plasma waves (SPWs). Moreover, surface plasma waves are a very efficient route to transfer the laser energy to the secondary sources including laser driven particle and radiation beams and to control and optimize the physical properties of these sources. We present here experimental evidence of a novel regime of the SPWs excitation by ultrahigh intensity laser field (I\textgreater 10$^{\mathrm{20\thinspace }}$W/cm$^{\mathrm{2}})$ on grating targets and its effect on high energy surface electron acceleration. The peak of the electron emission was detected at a laser incidence angle of 45\textdegree . The results indicate new conditions for resonant excitation of SPWs since in the limit of the linear regime (moderate intensities of \textasciitilde 10$^{\mathrm{19\thinspace }}$W/cm$^{\mathrm{2}}$ and step preplasma profile), the resonance angle is predicted at 30\textdegree . 2D PIC simulations and a novel analytical model confirm the experimental data and reveal that, at laser intensities above 10$^{\mathrm{20\thinspace }}$W/cm$^{\mathrm{2}}$, nonlinearities induced by the preplasma condition and relativistic effects change the SPWs resonance. [Preview Abstract] 

GP11.00041: An overview of LaserProduced Relativistic Positrons in the Laboratory Brandon Edghill, Gerald Williams, Hui Chen, Farhat Beg The production of relativistic positrons using ultraintense lasers can facilitate studies of fundamental pair plasma science in the relativistic regime and laboratory studies of scaled energetic astrophysical mechanisms such as gamma ray bursts. The positron densities and spatial scales required for these applications, however, are larger than current capabilities. Here, we present an overview of the experimental laserproduced positron results and their respective modeling for both the direct laserirradiated process and the indirect process (laser wakefield accelerated electrons irradiating a highZ converter). Conversion efficiency into positrons and positron beam characteristics are compared, including total pair yield, mean energy, angular divergence, and inferred pair density for various laser and target conditions. Prospects towards increasing positron densities and beam repetition rates will also be discussed. [Preview Abstract] 

GP11.00042: MultiGeV electronpositron pair generation from laserelectron scattering Marija Vranic, Ondrej Klimo, Georg Korn, Stefan Weber Positron generation in the laboratory is of great importance, both for fundamental science and potential applications. For laboratory astrophysics, it is particularly important to produce neutral electronpositron plasma, with properties that allow studying their collective behavior. Electronpositron pairs can be generated by first emitting an energetic photon, that later decays into a pair in an intense background field (BreitWheeler process). Recently, several experiments demonstrated that highfrequency radiation can be generated in laserelectron beam scattering. Here we propose a new scattering configuration that can both generate electronpositron pairs, and later accelerate them to multiGeV energies. This configuration allows obtaining an e+e flow with a higher energy than that of the initial electron beam. We develop an analytical model that predicts the energy cutoff. We discuss the number of pairs expected, the acceleration and the overall quality of the beam. We also study the role of pulse duration and spatiotemporal synchronization for the overall number of pairs. The work is supported by OSIRIS QEDPIC simulations, and these ideas can be tested with a new generation laser system at ELI Beamlines that will provide 10 PW peak power in a 150 fs pulse duration. [Preview Abstract] 

GP11.00043: Plasma diagnosis using the laserplasma terahertz(THz) radiation Keekon Kang, Dogeun Jang, Hyyong Suk There has been growing interest in laserplasma terahertz(THz) radiation as a source for plasma diagnostics for its strong radiation energy and broadband characteristics. Yet, it has not been used in actual diagnostics systems as its validity was not thoroughly investigated. In this work, we measured the plasma density in our inductivelycoupled plasma(ICP) chamber with the laserplasma THz radiation. The THz timedomain spectroscopy(THzTDS) and singleshot detection method were used for the detection of the THz. The diagnosis results from the two different detection methods were consistent with each other, giving a possibility of the realization of the laserplasmaTHzbased plasma diagnostics. [Preview Abstract] 

GP11.00044: Directed highpower THz radiation from transverse laser wakefield excited in an electron density filament Serge Kalmykov, Alexander Englesbe, Jennifer Elle, Matthew Domonkos, Andreas SchmittSody A tightly focused femtosecond, weakly relativistic laser pulse partially ionizes the ambient gas, creating a string (a ``filament'') of electron density, locally reducing the nonlinear index and compensating for the selffocusing effect caused by bound electrons. While maintaining the filament over many Rayleigh lengths, the pulse drives inside it a threedimensional (3D) wave of charge separation  the plasma wake. If the pulse waist size is much smaller than the Langmuir wavelength, electron current in the wake is mostly transverse. Electrons, driven by the wake across the sharp radial boundary of the filament, lose coherence within 23 periods of wakefield oscillations, and the wake decays [J.R. Marques et al., Phys. Plasmas 5, 1162 (1998)]. The laser pulse is thus accompanied by a shortlived, almost aperiodic electron current coupled to the sharp index gradient. The comprehensive 3D hydrodynamic model shows that this structure emits a broadband THz radiation, with the highest power emitted in the nearforward direction. The THz radiation pattern contains information on wake currents surrounding the laser pulse, thus serving as an alloptical diagnostic tool. The results are tested in cylindrical and full 3D PIC simulations using codes WAKE and EPOCH. [Preview Abstract] 

GP11.00045: Terahertz Radiation from Laser Created Plasma by Applying a Transverse Static Electric Field Noboru Yugami, Takuya Fukuda, Zhan Jin, Ryosuke Kodama, Hideo Nagatomo, Yasuhiko Sentoku, Hitoshi Sakagami Terahertz (THz) radiation, which is emitted in narrow cone in the forward direction from femtosecond laser pulse created plasma has been observed by N.Yugami \textit{et al}. [1]. Additionally, T. Loffler \textit{et al}. have observed that a significantly increased THz emission intensity in the forward direction when the transverse static electric field is applied to the plasma [2]. We propose the theoretical model of the THz radiation from laser created plasma by applying the transverse static electric field and conducted both experiments and 2DPIC simulation to compared with our theory.\\ \\$[1]$ N. Yugami \textit{et al}, Jpn. J. Appl. Phys. \textbf{45,} L1051 (2006). [2] T. Loffler \textit{et al}, Appl. Phys. Lett. \textbf{77}, 453 (2000). [Preview Abstract] 
(Author Not Attending)

GP11.00046: Highefficiency gammaray flash generation from multiplelaser scattering Zheng Gong, S. S. Bulanov, A. Arefiev, X. Q. Yan Gammaray flash generation in a nearcriticaldensity target irradiated by four symmetrical colliding laser pulses is numerically investigated. With peak intensities about $10^{23}$ W/cm$^2$, the laser pulses boost electron energy through direct laser acceleration, while pushing them inward with the ponderomotive force. After backscattering with counterpropagating laser, the accelerated electron is trapped in the electromagnetic standing waves of the ponderomotive potential well created by the coherent overlapping of the laser pulses. Electrons emit gamma ray photons in a multiplelaserscattering regime, where the electrons act as a medium transferring energy from the laser to gammarays in the ponderomotive potential valley [Z. Gong et al, PRE 95, 013210 (2017)]. [Preview Abstract] 

GP11.00047: Gammaray Radiation From Plasma Bubble Hosing Bifeng Lei, Sergey Rykovanov The CEPdominated few cycle strong ( \begin{figure}[htbp] \centerline{\includegraphics[width=0.40in,height=0.17in]{100720171.eps}} \label{fig1} \end{figure} ) laser pulse could oscillate in a underdense plasma with a period [1], \begin{figure}[htbp] \centerline{\includegraphics[width=1.03in,height=0.19in]{100720172.eps}} \label{fig2} \end{figure} , where \begin{figure}[htbp] \centerline{\includegraphics[width=0.14in,height=0.17in]{100720173.eps}} \label{fig3} \end{figure} is the laser wavelength, \begin{figure}[htbp] \centerline{\includegraphics[width=0.14in,height=0.17in]{100720174.eps}} \label{fig4} \end{figure} is the laser critical density and \begin{figure}[htbp] \centerline{\includegraphics[width=0.15in,height=0.18in]{100720175.eps}} \label{fig5} \end{figure} is the initial plasma density. This oscillation further leads to the hosinglike oscillation of the formed plasma bubble [2] which, in turn, gives a very strong oscillation strength for the electrons trapped inside. With numbers of selftrapped electrons, this scheme is capable server as a strong and bright gammaray source. A stretched plasma bubble is achieved by firstly injecting a symmetric, moderately long ( \begin{figure}[htbp] \centerline{\includegraphics[width=0.24in,height=0.18in]{100720176.eps}} \label{fig6} \end{figure} ) and strong ( \begin{figure}[htbp] \centerline{\includegraphics[width=0.40in,height=0.17in]{100720177.eps}} \label{fig7} \end{figure} ) laser in to an underdense plasma. Then, many electrons can be selftrapped along with the bubble breaking due to the nonlinear plasma wave. The head erosion produces the few cycle pulse which enables the oscillation. \textbf{References:} [1] A. A. Silaev et al., ResidualCurrent Excitation in Plasmas Produced by FewCycle Laser Pulses, PhysRevLett.102.115005 (2009); [2] M. C. Kaluza et al., Observation of a LongWavelength Hosing Modulation of a HighIntensity Laser Pulse in Underdense Plasma, Phys. Rev. Lett.~\textbf{105}, 095003 (2010). [Preview Abstract] 

GP11.00048: Temporal characterization of the wavebreaking flash in a laser plasma accelerator Bo Miao, Linus Feder, Andrew Goers, George Hine, Fatholah Salehi, Jared Wahlstrand, Daniel Woodbury, Howard Milchberg Wavebreaking injection of electrons into a relativistic plasma wake generated in nearcritical density plasma by subterawatt laser pulses generates an intense ($\sim$1$\mu$J) and ultrabroadband $(\Delta\lambda\sim300nm)$ radiation flash [1]. In this work we demonstrate the spectral coherence of this radiation and measure its temporal width using singleshot supercontinuum spectral interferometry (SSSI). The measured temporal width is limited by measurement resolution to ~50 fs. Spectral coherence is corroborated by PIC simulations which show that the spatial extent of the acceleration trajectory at the trapping region is small compared to the radiation center wavelength. To our knowledge, this is the first temporal and coherence characterization of wavebreaking radiation.\newline [1] Goers, A. J., et al. "MultiMeV electron acceleration by subterawatt laser pulses." Physical review letters 115.19 (2015): 194802. [Preview Abstract] 

GP11.00049: Impact of a plasma channel on the emission of directed highenergy photons in laserplasma interaction Oliver Jansen, Tao Wang, Toma Toncian, David Stark, Emmanuel d'Humieres, Alexey Arefiev \hfill \newline Compact sources of directed highenergy photons are of great interest in current research. Common sources of highenergy photons include synchrotrons and other large and expensive accelerators. Laserplasma interactions promise sources that are significantly smaller and cheaper than conventional ones. However, they come at the cost of producing either only small number of photons or very undirected ones. A recent study[1] shows, that the use of a plasma channel is able to significantly mitigate these problems while producing a large number of high energy, well collimated photons. We provide an analysis on the physical processes, that lead to the formation of strong magnetic fields responsible for this improvement of emission. Furthermore, we investigate the channel properties in relation to a given laser pulse.\\ \hfill \newline References: [1] Stark \textit{et al.} PRL {\bf 116},185003 (2016). [Preview Abstract] 

GP11.00050: XRay and electron beam source characterization from SelfModulated Laser Wakefield Acceleration experiments at Titan Paul King, Nuno Lemos, Felicie Albert, Jessica Shaw, Avi Milder, Ken Marsh, Art Pak, Bjorn Hegelich, Chan Joshi The development of a directional, lowdivergence, and shortduration (ps and subps) xray probes with energies of tens of keV is desirable for the fields of astrophysics, High Energy Density Science and Inertial Confinement Fusion. In this work we focused the Titan laser beam (1 ps and 150 Joules) into a 4mm helium gas jet to produce an electron beam that in turn generates an xray beam. The measured Raman Forward Scattering satellites present in the laser spectrum after the interaction, indicate the generation of a Selfmodulated laser wakefield accelerator. This accelerator produced an electron beam with energies up to 250 MeV, a divergence of 16 x 40 mrad and a total charge of 6 nC. Using this highcharge relativistic electron beam we explored the combination of three mechanisms to produce an xray beam: Betatron, Compton scattering and Bremsstrahlung. We show the generation of a low divergence (~mrad), small source size (~um) broadband (keV to MeV) xray beam that can be used as a backlighter for timeresolved spectroscopy, imaging, and Compton radiography. [Preview Abstract] 
(Author Not Attending)

GP11.00051: Dynamics of multiple interacting ultraintense lasers in a plasma Lucas Sa, Jorge Vieira, Ricardo Fonseca, Luis Silva, Warren Mori Although light beams do not interact in vacuum, two intense lasers can interact with each other in a nonlinear medium, forming spiraling and braiding patterns when they carry angular momentum. Here, we analyse the interaction between $N$ laser filaments. Using a variational approach based on the NonLinear Schr\"odinger Equation with the lowest order relativistic mass correction, we obtained a mechanical analog of an exponential $N$body problem for the beam centroids and spotsizes. We found that the $N$ beams can spiral in a circular motion around the center of mass analog and determined orbital parameters and trapping criteria for this motion. Furthermore, the lasers could form a “solar system”, with $N1$ beams orbiting a highpower one. The predictions for both models were tested in ParticleinCell simulations, in which other effects, namely noninstantaneous spatiotemporal nonlinearities, can be compared to the relativistic mass correction. Finally, the initial configuration of the beams could follow from filamentary processes, with the filamentation of an orbital angular momentum carrying laser originating the spiralling and braiding motions of the filaments. [Preview Abstract] 

GP11.00052: Coupling the photon kinetics of soft photons with high energy photons L. O. Silva, R. Bingham The description of electromagnetic fields based on the generalized photon kinetic theory, which takes advantage of the WignerMoyal description for the corresponding classical field theory, is capable of capturing collective plasma dynamics in the relativistic regime driven by broadband incoherent or partially coherent sources. We explore the possibility to extend this description to include the dynamics of hard photons in the plasma, whose interaction is dominated by single scattering processes. Examples of the modification of classical plasma instabilities due to the presence of hard photons is discussed. [Preview Abstract] 

GP11.00053: XRay Pulse Compression using Stimulated Brillouin Scattering in Plasma Matthew Edwards, Julia Mikhailova, Nathaniel Fisch Stimulated Brillouin scattering may allow cleaning and compression of the output from xray freeelectron lasers, producing coherent subfemtosecond pulses with intensities ordersofmagnitude beyond current sources. In contrast to stimulated Raman scattering, which is limited by damping at short wavelengths, particleincell simulations and analytic models suggest that amplification by Brillouin scattering is possible in soliddensity plasma at the wavelengths and intensities of freeelectron lasers. The nonlinear amplification process is robust to quasiincoherence in the pump beam, permitting beam cleaning in addition to compression.\footnote{M. R. Edwards, J. M. Mikhailova, and N. J. Fisch, ``Xray amplification by stimulated Brillouin scattering," arXiv:1705.08599, to appear in Phys. Rev. E (2017).} [Preview Abstract] 

GP11.00054: Development of PETAL diagnostics: PETAPhys project D. Raffestin, G. Boutoux, J. Baggio, D. Batani, N. Blanchot, D. Bretheau, S. Hulin, E. d'Humieres, F. Granet, Th. Longhi, Ch. Meyer, Q. Moreno, R. Nuter, J. Rault, V. Tikhonchuk Beginning of autumn 2017, PETAL, a Petawatt laser beam, will be operated for experiments on the LMJ facility at the CEA/ Cesta research center. The PETAPhys project provides a support to the qualification phase of the PETAL laser operation. Within the PETAPhys project, we are developing two simple and robust diagnostics permitting both to characterize the focal spot of the PETAL beam and to measure the hard Xray spectrum at each shot. The first diagnostic consists in optical imaging of the PETAL beam focal spot in the spectral range of the second and third harmonic radiation emitted from the target. The second diagnostic is a hard Xray dosimeter consisting in a stack of imaging plates (IP) and filters, either placed inside a reentrant tube or inserted close to target. Numerical simulations as well as experiments on small scale facilities have been performed to design these diagnostics. If available, preliminary results from PETAL experiments will be discussed. [Preview Abstract] 

GP11.00055: LaserBioplasma Interaction: Excitation and Suppression of the Brain Waves by the Multiphoton Pulsedoperated Fiber Lasers in the Ultraviolet Range of Frequencies V. Alexander Stefan The novel study of the laser excitationsuppression of the brain waves\footnote{Tae Kim et. al. Cortically projecting basal forebrain parvalbumin neurons regulate cortical gamma band oscillations, Proceedings of the National Academy of Sciences, vol. 112 no. 11, 35353540, (2015).} is proposed. It is based on the pulsedoperated multiphoton fiberlaser interaction with the brain parvalbumin (PV) neurons.\footnote{Stefan, APSMarch2017, Abstract: M1.00291; V. Alexander Stefan, Neurophysics\textit{, Stem Cell Physics, and Genomic Physics: BeatWaveDrivenFree Electron Laser Beam Interactions with the Living Matter}, (SUPress, La Jolla, CA, 2012); Stefan, APSPPD, 2016, Abstract: JP10.00166; V. Stefan, B. I. Cohen, C. Joshi, \textit{Science}, 243, 4890, (1989).\par } The repetition frequency matches the low frequency brain waves (5100 Hz); enabling the resonancescanning of the wide range of the PV neurons (the generators of the brain wave activity). The tunable fiber laser frequencies are in the ultraviolet frequency range, thus enabling the monitoring of the PV neuronDNA, within the 10s of milliseconds. In medicine, the method can be used as an ``instantaneousonoff anesthetic.'' [Preview Abstract] 

GP11.00056: Thin film compression of a high rep rate laser: towards singlecycle pulse generation Deano Farinella, Sergey Mironov, Tam Nguyen, Matthew Stanfield, Franklin Dollar, Toshiki Tajima Thin Film Compression (TFC) has been proposed [1] as a means of increasing the peak power of ultrashort laser pulses with millijoule and greater energies. As opposed to increasing peak power by increasing the energy of the pulse, TFC instead achieves an amplification in peak power by compressing laser pulse length at a fixed energy. This pulse compression is accomplished by the generation of linearly chirped bandwidth through selfphase modulation, which is then recompressed by dispersive optics. A summary of the results of laser pulse compression experiments towards the production of singlecycle pulses will be presented. Simulations show [1] that laser pulses compressed to the singlecycle regime have the potential to generate singlecycle xray pulses which could be used to generate wakefields in soliddensity plasma with acceleration gradients of up to TeV/cm [2]. [1] G. Mourou et al., Eur. Phys. J. 223, 1181 (2014) \newline [2] T. Tajima, Eur. Phys. J. 223, 1037 (2014); X.M. Zhang et al., Phys. Rev. Accel Beams. 19, 101004 (2016) [Preview Abstract] 

GP11.00057: Narrow bandwidth LaserPlasma Accelerator driven Thomson photon source development C.G.R. Geddes, H.E. Tsai, G. Otero, X. Liu, J. van Tilborg, Cs. Toth, J.L. Vay, R. Lehe, C.B. Schroeder, E. Esarey, A. Friedman, D.P. Grote, W.P. Leemans Compact, highquality photon sources at MeV energies can be provided by Thomson scattering of a laser from the electron beam of a LaserPlasma Accelerator (LPA). Recent experiments and simulations demonstrate controllable LPAs in the energy range appropriate to MeV sources. Simulations indicate that high flux with narrow energy spread can be achieved via control of the scattering laser pulse shape and laser guiding, and that undesired background bremsstrahlung can be mitigated by plasma based deceleration of the electron beam after photon production. Construction of experiments and laser capabilities to combine these elements will be presented, along with initial operations, towards a compact photon source system. Work supported by US DOE NNSA DNN R&D and by Sc. HEP under contract DEAC0205CH11231. [Preview Abstract] 

GP11.00058: PLASMA TECHNOLOGY 

GP11.00059: DIIID 

GP11.00060: Developing DIIID To Prepare For ITER And The Path To Fusion Energy Richard Buttery, David Hill, Wayne Solomon, Houyang Guo DIIID pursues the advancement of fusion energy through scientific understanding and discovery of solutions. Research targets two key goals. First, to prepare for ITER we must resolve how to use its flexible control tools to rapidly reach Q$=$10, and develop the scientific basis to interpret results from ITER for fusion projection. Second, we must determine how to sustain a high performance fusion core in steady state conditions, with minimal actuators and a plasma exhaust solution. DIIID will target these missions with: (i) increased electron heating and balanced torque neutral beams to simulate burning plasma conditions (ii) new 3D coil arrays to resolve control of transients (iii) off axis current drive to study physics in steady state regimes (iv) divertors configurations to promote detachment with low upstream density (v) a reactor relevant wall to qualify materials and resolve physics in reactorlike conditions. With new diagnostics and leading edge simulation, this will position the US for success in ITER and a unique knowledge to accelerate the approach to fusion energy. [Preview Abstract] 

GP11.00061: Parameter exploration for a Compact Advanced Tokamak DEMO D.B. Weisberg, R.J. Buttery, J.R. Ferron, A.M. Garofalo, P.B. Snyder, A.D. Turnbull, C.T. Holcomb, J. McClenaghan, J. Canik, JM Park A new parameter study has explored a range of design points to assess the physics feasibility for a compact 200MWe advanced tokamak DEMO that combines high beta ($\beta_N<4$) and high toroidal field ($B_T=67$T). A unique aspect of this study is the use of a FASTRAN modeling suite that combines integrated transport, pedestal, stability, and heating & current drive calculations to predict steadystate solutions with neutral beam and helicon powered current drive. This study has identified a range of design solutions in a compact ($R_0=4$m), highfield ($B_T=67$T), stronglyshaped ($\kappa=2$, $\delta=0.6$) device. Unlike previous proposals, CAT DEMO takes advantage of highbeta operation as well as emerging advances in magnet technology to demonstrate net electric production in a moderately sized machine. We present results showing that the large bootstrap fraction and low recirculating power enabled by high normalized beta can achieve tolerable heat and neutron load with good Hmode access. The prediction of operating points with simultaneously achieved highconfinement ($H_{98}<1.3$), highdensity ($f_{GW}<1.3$), and highbeta warrants additional assessment of this approach towards a costattractive DEMO device. [Preview Abstract] 

GP11.00062: A U.S. Strategy for Timely Fusion Energy Development Mickey Wade Worldwide energy demand is expected to explode in the latter half of this century. In anticipation of this demand, the U.S. DOE recently asked the National Academy of Science to provide guidance on a longterm strategic plan assuming that ``economical fusion energy within the next several decades is a U.S. strategic interest.`` Delivering on such a plan will require an R{\&}D program that delivers key data and understanding on the building blocks of a) burning plasma physics, b) optimization of the coupled coreedge solution, and c) fusion nuclear science to inform the design of a costattractive DEMO reactor in this time frame. Such a program should leverage existing facilities in the U.S. program including ITER, provide substantive motivation for an expanding R{\&}D scope (and funding), and enable timely redirection of resources within the program as appropriate (and endorsed by DOE and the fusion community). This paper will outline a potential strategy that provides worldleading opportunities for the research community in a range of areas while delivering on key milestones required for timely fusion energy development. [Preview Abstract] 

GP11.00063: Creating Hybrid Plasmas With OffAxis ECCD for Radiating Divertor Studies in DIIID C.C. Petty, J.R. Ferron, T.C. Luce, T.H. Osborne, T.W. Petrie, F. Turco, C.T. Holcomb, K.E. Thome A long duration, high density, high power hybrid scenario has been developed for use in radiative divertor studies in DIIID. Using 11.2 MW of coNBI power and 3.4 MW of ECCD, with a total injected energy of up to 56 MJ, high performance hybrid plasmas with $\beta_{\mathrm{N\thinspace }}=$ 3.7 and H$_{\mathrm{98y2\thinspace }}=$ 1.5 were created. The hybrid plasmas were fully noninductive at densities of n $\approx $ 4.2 \texttimes 10$^{\mathrm{19}}$ m$^{\mathrm{3}}$ with central ECCD, but the EC deposition needed to be moved to $\rho \quad =$ 0.45 to avoid the righthand cutoff when the density was raised to n $\approx $ 5.8 \texttimes 10$^{\mathrm{19}}$ m$^{\mathrm{3}}$ for radiative divertor studies. Although moving the EC deposition to $\rho \quad =$ 0.45 had the effect of dropping $\tau_{\mathrm{E}}$ by 10{\%}, the energy confinement time increased with higher density like $\tau_{\mathrm{E\thinspace }}\propto $ n$^{\mathrm{0.4}}$, allowing high beta to be maintained. While the plasma current profile displays the usual selforganizing properties of hybrids  an anomalously broad profile with q$_{\mathrm{min\thinspace }}$\textgreater 1  local current drive can still have a measurable effect on stability, either positively or negatively. For example, hybrid discharges with radial ECH deposited at $\rho \quad =$ 0.45 proved to be more robustly stable to n $=$ 1 modes (can be either a 1/1 or 2/1 mode) than similar discharges with coECCD at the same location. Interestingly, the large 1/1 mode had almost no effect on energy confinement but strongly degraded particle confinement; thus this mode needed to be suppressed to achieve the high pedestal densities required for radiative divertor studies. [Preview Abstract] 

GP11.00064: Energy Confinement Improvement with Density in Gas Puff Fueled High Performance Hybrid Plasmas on DIIID. T.H. Osborne, T.W. Petrie, A.W. Leonard, T.C. Luce, C.C. Petty, F. Turco, M.E. Fenstermacher, C.J. Lasnier, J.G. Watkins In contrast to behavior at moderate NBI heating, an increase in energy confinement is observed in high power, near double null, hybrid discharges in response to D2 gas puff fueling. This difference is tied to how the Hmode pedestal responds to fueling. At low power the pedestal width decreases with gas puff resulting in a strong reduction in the critical pressure gradient for the ballooning branch of the peelingballooning mode. At high power the pedestal width remains fixed and access to high pedestal pressure gradient with increased collisionality along the peeling boundary is maintained, allowing the pedestal pressure to increase with density. Access to the high pressure gradient peeling limited regime is also blocked by the ballooning boundary if the shape departs from near double null or q decreases relative to the favorable conditions: DRSEP $\approx $ 2.5mm, q95 $\approx $ 6. [Preview Abstract] 

GP11.00065: Magnetic Flux Conversion in the DIIID SteadyState Hybrid Scenario* N.Z. Taylor, T.C. Luce, R.J. La Haye, C.C. Petty, R. Nazikian The hybrid is a promising high confinement scenario for ITER. The broader current profile aids discharge sustainment by raising $q_{min} >$ 1 thereby avoiding sawtoothtriggered 2/1 tearing modes. In DIIID hybrid scenario discharges, the rate of poloidal magnetic energy consumption is more than the rate of energy flow from the poloidal field coils. This is evidence that there is a conversion of toroidal flux to poloidal flux, which may be responsible for the anomalous broadening of the current profile known as flux pumping. The rate of poloidal flux being provided and consumed was tracked with coil and kinetic flux states [1]. During long stationary intervals (~1.5 seconds) with constant stored magnetic energy, a significant flux state deficit rate $>$10 mV was observed. The inequality in the evolution of the flux states was observed in hybrids that were 100$\%$ noninductive and with successful RMP ELM suppression.\\ $\ast$Work supported by the US DOE under DEFC0204ER54698 and DEAC0506OR23100. [1] T.C. Luce, Nuclear Fusion {\bf 54}, 093005 (2014) [Preview Abstract] 

GP11.00066: Reduced turbulence and Hmode confinement in Lmode negative triangularity discharges on DIIID A. Marinoni, M.E. Austin, M.L. Walker, A.W. Hyatt, C.C. Petty, K.H. Thome, M. Porkolab, J.C. Rost, E.M. Davis, G.R. Mckee, T.L. Rhodes, C. Sung, O. Sauter DIIID has produced innerwall limited plasmas with an Lmode edge at negative triangularity characterized by confinement and fluctuation levels comparable to those in Hmode plasmas at positive triangularity. On TCV, similar plasmas at low collisionality and with pure electron heating showedimproved energy confinement, as compared to matched discharges at positive triangularity, due to modifications to the toroidal precession drift of trapped electrons. The recent DIIID experiment used both ECH and NBI heating, thus exploring a more reactor relevant regime where Te\textasciitilde Ti. Compared to matched positive triangularity discharges, the intensity of density and temperaturefluctuations is reduced at negative triangularity both in ECH and in NBI dominated phases. Preliminary TGLF runs indicate the discharges are dominated by TEM modes. More detailed analysis will explore the role of the toroidal precession drift in this new regime. [Preview Abstract] 

GP11.00067: Turbulent Ion Fluctuation Measurements in Negative Triangularity Plasmas Dinh Truong, George McKee, Zheng Yan, Raymond Fonck, Max Austin, Alessandro Marinoni A new detector array on the UFCHERS (Ultra Fast CHarge Exchange Recombination Spectroscopy) diagnostic at DIIID has resulted in significantly improved signal to noise ratio and sensitivity to ion thermal fluctuations. UFCHERS measures local, longwavelength Carbon density, ion temperature, and toroidal velocity fluctuations at turbulencerelevant spatiotemporal scales (1 $\mu $s time resolution, \textasciitilde 1 cm spatial resolution which is approximately the turbulence correlation length) from emission of the CVI n$=$8$\to $7 transition. UFCHERS and BES fluctuation measurements were obtained in equivalent positive and negative triangularity ($\delta )$ discharges with an Lmode edge to compare with theoretical models of turbulencedriven transport and elucidate the mechanisms for improved confinement with negative$\delta $. Finite coherence is observed between UFCHERS and colocated BES channels, demonstrating that critical multifield fluctuations such as \textless n*T$_{\mathrm{i}}$\textgreater and \textless n*v$_{\mathrm{tor}}$\textgreater can be measured. Initial analysis shows positive$\delta $ has radially decreasing, low coherency between \textasciitilde 20200 kHz for main ion density (BES) and Carbon density, ion temperature, and toroidal rotation (UFCHERS) fluctuations. [Preview Abstract] 

GP11.00068: A Conformal Conducting Wall for Robust Stability of High $\beta_N$, Fully Noninductive Discharges in DIIID J.R. Ferron, J. Bialek, J. Hanson, G. Navratil, J.M. Park A conducting surface inside the DIIID vacuum vessel, closer to the plasma, can increase the idealwall MHD stability limit above the high normalized beta ($\beta_N$) needed for 100\% noninductivelydriven current at power plant relevant $q_{95}$. In discharges modeled with the planned heating/current drive upgrades, the required $\beta_N$ is as high as 5. This is roughly the calculated limit for n = 1 idealwall stability, even with a broad current density profile designed to couple well to the present conducting wall. Tearing and resistive wall modes will very likely limit $\beta_N$ to a value that is lower, but which is expected to scale with the idealwall limit. Conceptual designs for an axisymmetric wall that better matches the plasma shape raise the idealwall stability limited $\beta_N$ above 7. Analysis with VALEN of a 3D wall model predicts $\beta_N\sim 6.4$. Increased stability margins are also expected for a wide range of DIIID discharge scenarios even without a broad current density profile. [Preview Abstract] 

GP11.00069: Developing on DIIID a QHmode edge solution for Q$=$10 in ITER. A.M. Garofalo, C. PazSoldan, D.B. Weisberg, T.M. Wilks, J.M. Hanson, N.C. Logan, C.M. Samuell Experiments on DIIID are advancing toward a demonstration of access to and control of Q(uiescent)Hmode at normalized performance equivalent to Q$=$10 in plasmas with ITER shape and collisionality, and low NBI torque throughout the pulse length. Earlier experiments had shown that ELMs return at NBI torque magnitude below \textasciitilde 3.5 Nm, which is above the expected level of normalized torque input in ITER. Recent experiments have been able to extend QHmode operation to lower torque \textasciitilde 2 Nm and higher energy confinement by increasing the plasmawall gap at the outboard midplane, and by reducing the input energy of the beaminjected ions. Two hypotheses are being tested: (a) the outer gap affects the scrapeoff layer flows and thus the rotation gradient at the edge of the plasma, known to affect QHmode access; (b) fast ion losses bombarding the wall may release impurities that affect the edge collisionality and stability making QHmode operation more difficult. [Preview Abstract] 

GP11.00070: Mutually Exclusive Relation between High Pedestal and LargeRadius Internal Transport Barrier in High Betap Scenario on DIIID Siye Ding, Jinping Qian, Juan Huang, Xianzu Gong, Tianyang Xia, Chengkang Pan, Guoqiang Li, Qilong Ren, Wenfeng Guo, Andrea Garofalo, Chris Holcomb, Joseph McClenaghan Statistical analysis of experimental data from DIIID high betap plasmas implies that a natural boundary exists hindering the plasma to simultaneously achieve high pedestal (electron temperature and density) and strong largeradius internal transport barrier (ITB) . In the previous study, we revealed a betap threshold about 1.9 for the formation of largeradius ITB in both Te and ne channels. With strong gas puffing, we observed higher betap threshold (about 2.2) for the formation of neITB that may be due to (1) the higher edge density and pedestal height and therefore high local bootstrap current; (2) the penetration of edge inductive current and turbulence. Meanwhile, the betap threshold for the formation of TeITB doesn't change. The observed mutually exclusive relation in experiments is important because sustaining a largeradius ITB is favorable for developing high betap scenario with optimized confinement and stability. [Preview Abstract] 

GP11.00071: Stability analysis of the high poloidal bet scenario on DIIIDtowards operation athigher plasma current W.F. Guo, X.Z. Gong, J. Huang, Q.L. Ren, J.P. Qian, S.Y. Ding, C.K. Pan, G.Q. Li, T.Y. Xia, A.M. Garofalo, L. Lao, A. Hyatt, J. Ferron, O. Meneghini, Y.Q. Liu, J. McClenaghan, C.T. Holcomb The high poloidal beta scenario with plasma current I$^{\mathrm{P}}$\textasciitilde 600 kA and largeradius internal transport barrier (ITB) on DIIID is subject to n$=$1 MHD kink modes when the current profile becomes very broad at internal inductance values li\textasciitilde 0.50.6. It is desirable to extend this scenario to higer plasma current (\textasciitilde 1 MA) for highernormalized fusionperformance. However, higher current at constant normalized beta, ?$^{\mathrm{N}}$\textasciitilde 3, would reducethe poloidal bet, ?$^{\mathrm{P}}$, below the threshold for ITB sustainment, observed at ?$^{\mathrm{P}}$\textasciitilde 1.9. Thus, to avoid loss ofthe IT,?$^{\mathrm{N??}}$ must be increased together with I$^{\mathrm{P}}$ while avoiding the kink instability. MHD analysis is presented that explains possible paths to high?$^{\mathrm{N}}$stability limit for the kink mode in tis scenario. *Work supported by National Magnetic Confinement Fusion Program of Chin under 2015GB110001 and 2015GB102000£¬National Natural Science Foundation of China under Grant No. 1147521 and by US DOE under DEFC0204ER54698. [Preview Abstract] 

GP11.00072: Extension of high poloidal beta scenario in DIIID to lower q95 for steady state fusion reactor J. Huang, X. Gong, J. Qian, S. Ding, Q. Ren, W. Guo, C. Pan, G. Li, T. Xia, A. Garofalo, L. Lao, A. Hyatt, J. Ferron, C. Collins, D. Lin, G. Mckee, T. Rhode, J. McClenaghan, C. Holcomb, L. Cui, W. Heidbrink, Y. Zhu DIIID/EAST joint experiments have improved the high poloidal beta scenario with sustained largeradius internal transport barrier (ITB) extended to high plasma current I$_{\mathrm{p}}$\textasciitilde 1MA with q95\textasciitilde 6.0. Slight offaxis NBCD is applied to obtain broader current density profile, ITBs can now be sustained below the previously observed $\beta_{\mathrm{p}}$ threshold with excellent confinement (H$_{\mathrm{98y2}}$\textasciitilde 1.8). The scenario also exhibits a local negative shear appearing with q increased at rho\textasciitilde 0.4, which helps ITB formation and sustainment. This confirms TGLF prediction that negative magnetic shear can help recover ITB and achieve high confinement with reduced q95. Detailed analysis shows that the Shafranov shift and q profile is critical in the ITB formation at high $\beta _{\mathrm{p\thinspace }}$regime. [Preview Abstract] 

GP11.00073: Central Safety Factor and Normalized Beta Control Under NearZero Input Torque Constraints in DIIID Andres Pajares, William Wehner, Eugenio Schuster, Keith Burrell, John Ferron, Michael Walker, David Humphreys DIIID experiments have assessed the capability of combined central safety factor (q$_{\mathrm{0}})$ and normalized beta ($\beta_{\mathrm{N}})$ control under nearzero net torque to facilitate access to QHmode with reverse I$_{\mathrm{p}}$ and normal B$_{\mathrm{t}}$. Regulation of q$_{\mathrm{0}}$ and $\beta_{\mathrm{N}}$ can prevent magnetohydrodynamic instabilities that deteriorate plasma performance in discharges with a monotonically increasing safetyfactor profile. Zeroinputtorque scenarios are of special interest because future burning plasma tokamaks such as ITER will most likely operate with very low input torque, which makes these scenarios more susceptible to locked modes. To support studies of such scenarios, a controller for simultaneous regulation of q$_{\mathrm{0}}$ and $\beta_{\mathrm{N}}$ has been developed using nearzero net input torque actuators including balanced neutral beam injection (NBI) and electroncyclotron heating {\&} current drive (ECH/ECCD). Experimental results show that in spite of the presence of locked modes the use of feedback control resulted in good tracking of the commanded q$_{\mathrm{0}}$ and $\beta_{\mathrm{N}}$ when both ECCD/ECH and NBI were available. [Preview Abstract] 

GP11.00074: Predictive Rotation Profile Control for the DIIID Tokamak W.P. Wehner, E. Schuster, M.D. Boyer, M.L. Walker, D.A. Humphreys Controloriented modeling and modelbased control of the rotation profile are employed to build a suitable control capability for aiding rotationrelated physics studies at DIIID. To obtain a controloriented model, a simplified version of the momentum balance equation is combined with empirical representations of the momentum sources. The control approach is rooted in a Model Predictive Control (MPC) framework to regulate the rotation profile while satisfying constraints associated with the desired plasma stored energy and/or $\beta_{\mathrm{N\thinspace }}$limit. Simple modifications allow for alternative control objectives, such as maximizing the plasma rotation while maintaining a specified input torque. Because the MPC approach can explicitly incorporate various types of constraints, this approach is well suited to a variety of control objectives, and therefore serves as a valuable tool for experimental physics studies. Closedloop TRANSP simulations are presented to demonstrate the effectiveness of the control approach. [Preview Abstract] 

GP11.00075: Effects of Plasma Shaping on Intrinsic Rotation in DIIID J.S. deGrassie, T.H. Osborne, B.A. Grierson, G.R. McKee, T.L. Rhodes Intrinsic rotation in an axisymmetric tokamak must have its source in a momentum flux that passes through the boundary of the plasma. Since it is wellknown that shaping in diverted discharges modifies the pedestal in Hmode discharges [1], we have performed experiments on DIIID in which the shaping is changed during a discharge and the accompanying change in the intrinsic rotation profile is measured. We see that the change in intrinsic rotation magnitude in the outer plasma region, rho $=$ 0.7, is correlated with the plasma stored energy to a large extent. At the next level of response, there are changes in the rotation profiles related to the pedestal pressure, and in the interior possibly to the q profile. An additional focus of these experiments was to make measurements of the shapeinduced changes in turbulence strength and spectra with Beam Emission Spectroscopy and Doppler Back Scattering. Both show clear changes in frequency with, for example, a change in the major radius of the Xpoint in a single null diverted plasma. [1] R.J. Groebner et al, Nucl. Fusion \textbf{49}, 085037 (2009). [Preview Abstract] 

GP11.00076: Scaling of Intrinsic Rotation with Normalized Gyroradius in DIIID and Comparison to Intrinsic Torque Scaling Colin Chrystal, Shaun Haskey, Brian Grierson, John deGrassie, Cameron Samuell New experiments at DIIID have investigated the scaling of intrinsic rotation with the normalized gyroradius, $\rho $*, by performing a dimensionless parameter scan in electron cyclotron heated Hmode plasmas with no external torque injection. Intrinsic rotation was measured for both the dominant impurity and the mainion species. The main experimental result is that the Mach no. (toroidal velocity normalized to either the sound speed or the Alfven velocity) was nearly constant or slightly increasing with decreasing $\rho $*. These intrinsic rotation results corroborate the previous measurements$^{\mathrm{1}}$ of the intrinsic torque and momentum confinement time scaling with $\rho $*, which indicates that the fastion content from significant neutral beam injection in the previous experiment did not influence those results. The potential effect of neutral particle transport in the pedestal is also investigated. Predictions of the intrinsic rotation in ITER are reviewed. [Preview Abstract] 

GP11.00077: Reynolds StressDriven Edge Momentum Transport in DIIID Jose Boedo, D. Rudakov, J. deGrassie, B. Grierson, A. Ashourvan Tokamak plasma rotate toroidally due to an intrinsic edge source [1]. Reynolds Stress has been proposed $\langle$nv$_\phi$v$_\rho$$\rangle$=$\langle$n$\rangle$$\langle$\tilde{v}$_\phi$ \tilde{v}$_\rho$$\rangle$+$\hspace{0mm}$$\langle$v$_\phi$$\rangle$$\langle$\~n$_\phi$\tilde{v}$_\rho$$\rangle$+$\hspace{0mm}$$\langle$\tilde{n}$\tilde{v}$_\phi$\tilde{v}$_\rho$$\rangle$ as the transport mechanism. The term $\langle$n$\rangle$$\langle$\tilde{v}$_\phi$\tilde{v}$_\rho$$\rangle$ peaking $\sim$1e26m$^\wedge$1s$^\wedge$2 just inside the separatrix, causes a significant inward pinch due to crossphase effects while the outward convection term, $\langle$v$_\phi$$\rangle$$\langle$$\tilde{n}$\tilde{v}$_\rho$$\rangle$, peaking at $\sim$1E26m$^\wedge$1s$^\wedge$2 roughly balances it. Surprisingly, the triple correlation term, $\langle$\tilde{n}$\tilde{v}$_\rho$\tilde{v}$_\phi$$\rangle$ peaking at t$\sim$1E25m$^\wedge$1s$^\wedge$2 becomes important as other terms almost null out. A rough momentum balance finds that the momentum flux from the RS term can explain the observed momentum balance. [Preview Abstract] 

GP11.00078: Collisionality and temperature dependence of the edge mainion cocurrent rotation profile feature on DIIID Shaun Haskey, Brian Grierson, Arash Ashourvan, Devon Battaglia, Colin Chrystal, Keith Burrell, Richard Groebner, John deGrassie, Luke Stagner, Timothy StoltzfusDueck, Novimir Pablant A new edge mainion (D$^{\mathrm{+}})$ CER system and upgraded edge impurity system are revealing clear differences between the mainion and dominant impurity (C$^{\mathrm{6+}})$ toroidal rotation from the pedestal top to the scrape off layer on DIIID with implications for intrinsic rotation studies. A peaked cocurrent edge toroidal rotation is observed for the main ion species near the outboard midplane separatrix with values up to 140km/s for low collisionality QH modes. In lower power (P$_{\mathrm{NBI}}=$0.8MW) Hmodes the edge rotation is still present but reduced to \textasciitilde 50km/s. D$^{\mathrm{+}}$ and C$^{\mathrm{6+}}$ toroidal rotation differences are presented for a variety of scenarios covering a significant range of edge collisionality and T$_{\mathrm{i}}$. Observations are compared with predictions from several models including collisionless ion orbit loss calculations and more complete modeling using the XGC0 code, which also predicts 140km/s edge rotation for low collisionality QH mode cases. [Preview Abstract] 

GP11.00079: Isotope Mass Scaling of Turbulence and Transport* George McKee, Zheng Yan, Punit Gohil, Tim Luce, Terry Rhodes The dependence of turbulence characteristics and transport scaling on the fuel ion mass has been investigated in a set of hydrogen $(A=1)$ and deuterium $(A=2)$ plasmas on DIIID. Normalized energy confinement time $(B*\tau_{E})$ is two times lower in hydrogen (H) plasmas compare to similar deuterium (D) plasmas. Dimensionless parameters other than ion mass $(A)$, including $\rho^{*}$, $q_{95}$, $T_{e}/T_{i}$, $\beta_{N}$, $\nu^{*}$, and Mach number were maintained nearly fixed. Matched profiles of electron density, electron and ion temperature, and toroidal rotation were well matched. The normalized turbulence amplitude $(\tilde{n}/n)$ is approximately twice as large in H as in D, which may partially explain the increased transport and reduced energy confinement time. Radial correlation lengths of lowwavenumber density turbulence in hydrogen are similar to or slightly larger than correlation lengths in the deuterium plasmas and generally scale with the ion gyroradius, which were maintained nearly fixed in this dimensionless scan. Predicting energy confinement in DT burning plasmas requires an understanding of the large and beneficial isotope scaling of transport. [Preview Abstract] 

GP11.00080: Impact of Magnetic Island  Turbulence MultiScale Interaction on Plasma Confinement and Magnetic Island Stability L. Bardoczi, T.A. Carter, R.J. La Haye, T.L. Rhodes, G.R. McKee Recent measurements$^{1}$ and gyrokinetic simulations$^{2}$ reported the reduction of turbulent density fluctuations (ñ) inside magnetic islands, and ñ increase outside magnetic islands, when the island width (W) exceeds a threshold (W$_{T}$). As the crossfield transport is dominantly driven by ñ, this calls into question the conventional understanding of confinement ($\tau$$_{e}$) degradation and Neoclassical Tearing Mode (NTM) stability physics. We report that the increase in ionscale ñ outside the island correlates with higher heat and particle fluxes, i.e., ñ increases temporarily when $\tau$$_{e}$ is decreasing, while in the following stationary state ñ is comparable to before NTM onset. This indicates that the decrease of the plasma stored energy results from ñNTM interaction. On the other hand, simultaneous ñ reduction at the Opoint has a destabilizing effect on NTMs. These observations suggest that driving ñ at the Opoint could prevent small islands from growing large, allowing better plasma confinement and safer tokamak operation. [1] Bardóczi, L. et al. Phys. Plasmas 24, 056106 (2017) [2] Navarro, A. B. et al. Plasma Phys. Control. Fusion 59, 034004 (2017) [Preview Abstract] 

GP11.00081: Particle transport in DIIID plasmas Peter Kress, Saskia Mordijck By analyzing the plasma opacity and density evolution during the ELM cycle in DIIID Hmode plasmas in which the amount of gas fueling was altered, we find evidence for an inward particle pinch at the plasma edge which seems to become more pronounced at higher density. Furthermore, at the plasma edge we find a correlation between the pedestal density and opacity, which measures neutral penetration depth. The changes in edge opacity during an ELM cycle were calculated by using a detailed time history of measured plasma profiles. At the same time, the density evolution during an ELM cycle was investigated. We find that if the edge density increases through an increase in gas fueling, then opacity increases and neutral fueling penetration depth decreases. We also find that density at the top of the pedestal recovers faster following an ELM when the overall density level is higher, leading to a hollow profile inside of the pedestal top. All these results indicate that there must be an inward particle pinch in the pedestal which will be crucial in the fueling of future burning plasma devices. [Preview Abstract] 

GP11.00082: Microtearing instabilities and resulting electron thermal transport in DIIID discharges A.H. Kritz, T. Rafiq, L. Luo, J. Weiland A reduced transport model for microtearing modes (MTMs), has been developed for use in integrated predictive modeling studies. A unified fluid/kinetic approach is employed in the derivation of the nonlinear MTM dispersion relation. The dependence of the MTMs real frequency and growth rate in DIIID like Lmode and Hmode plasma discharges is examined for a range of plasma parameters. The saturated amplitude of the magnetic fluctuations is calculated utilizing numerically determined MTM eigenvalues in the nonlinear MTM envelope equation. It is found that the electron temperature gradient in the presence of moderate collision frequency is required for MTMs to become unstable. The effects of small and large collisionality and small and large wavenumbers on MTMs are found to be stabilizing, while the effects of density gradient, plasma beta, low current density, and large magnetic shear are found to be destabilizing. The MTM growth rate, magnetic fluctuation strength, as well as electron thermal diffusivity is found to be larger in the Hmode plasma than in the Lmode plasma. [Preview Abstract] 

GP11.00083: Extracting 3D Information from 1D and 2D Diagnostic Systems on the DIIID Tokamak Michael Brookman The interpretation of tokamak data often hinges on assumptions of axisymetry and flux surface equilibria, neglecting 3D effects. This work discusses examples on the DIIID tokamak where this assumption is an insufficient approximation, and explores the diagnostic information available to resolve 3D effects while preserving 1D profiles. Methods for extracting 3D data from the electron cyclotron emission radiometers, density profile reflectometer, and Thomson scattering system are discussed. Coordinating diagnostics around the tokamak shows the significance of 3D features, such as sawteeth[1] and resonant magnetic perturbations. A consequence of imposed 3D perturbations is a shift in major radius of measured profiles between diagnostics at different toroidal locations. Integrating different diagnostics requires a database containing information about their toroidal, poloidal, and radial locations. Through the data analysis framework OMFIT, it is possible to measure the magnitude of the apparent shifts from 3D effects and enforce consistency between diagnostics. Using the existing 1D and 2D diagnostic systems on DIIID, this process allows the effects of the 3D perturbations on 1D profiles to be addressed. [Preview Abstract] 

GP11.00084: Measurement of internal equilibrium and fluctuating magnetic field on DIIID by using Radial PolarimeterInterferometer Jie Chen, Weixing Ding, David Brower, Rejean Boivin A Faradayeffect based Radial InterferometerPolarimeter (RIP) has been implemented on DIIID for measurements of the magnetic equilibrium and the magnetic axis vertical position with fast time response that can be exploited for position and instability control. Furthermore, RIP can also measure internal radial magnetic fluctuations, e.g. internal kink  precursor to sawtooth crash, NTM seeding and plasma disruptions. By utilizing counterrotating circular polarization technique, the diagnostic measures Faraday rotation and lineintegrated electron density simultaneously with time response at microsecond scale and phase noise \textasciitilde 0.01 degree/sqrt(kHz), corresponding to 1 Gs/sqrt(kHz) for typical DIIID plasma conditions. Measurement errors has been assessed and minimized. Systematic comparison between RIP measurement and MSEconstrained EFIT using a synthetic diagnostic shows good agreement, manifesting consistency of internal magnetic field measurement between RIP and other magnetic diagnostics. \textit{*Supported by USDOE grants DEFG0301ER54615 and DEFC0204ER54698.} [Preview Abstract] 

GP11.00085: Synthetic Diagnostic for Doppler Backscattering (DBS) Turbulence Measurements based on Full Wave Simulations D. R. Ernst, T. L. Rhodes, S. Kubota, N. Crocker Plasma fullwave simulations of the DIIID DBS system including its lenses and mirrors are developed using the GPUbased FDTD2D code [1], verified against the GENRAY raytracing code and TORBEAM paraxial beam code. Our semianalytic description of the effective spot size for a synthetic diagnostic reveals new focusing and defocusing effects arising from the combined effects of the curvature of the reflecting surface and that of the Gaussian beam wavefront. We compute the DBS transfer function from fullwave simulations to verify these effects. Using the synthetic diagnostic, nonlinear GYRO simulations closely match DBS fluctuation spectra with and without strong electron heating, without adjustment or change in normalization, while both GYRO and GENE also match fluxes in all transport channels [2]. Density gradient driven TEMs that are observed by the DBS diagnostic on DIIID are reproduced by simulations as a band of discrete toroidal mode numbers which intensify during strong electron heating.\newline [1] B. C. Rose, S. Kubota, and W. A. Peebles, in Proc. 18th Topical HTPD Conference (Wildwood, N.J., 2010). Also J. Hillesheim et al., Rev. Sci. Instrum. 83, 10E331 (2012).\newline [2] D. R. Ernst et al., Phys. Plasmas 23, 056112 (2016). Also 2014 IAEA FEC paper CN221/EX/23. [Preview Abstract] 

GP11.00086: DIIID Neutron Measurement: Status and Plan for Simplification and Upgrade Y.B. Zhu, W.W. Heidbrink, P.L. Taylor, D. Finkenthal Neutron diagnostics play key essential roles on DIIID. Historically an 18channel 2.45MeV DD neutron measurement system based on $^{\mathrm{3}}$He and BF$_{\mathrm{3}}$ proportional counters was inherited from DoubletIII including associated electronics and CAMAC data acquisition. Three fission chambers and two neutron scintillators were added in the 1980s and middle 1990s respectively. For Tritium burnup studies, two 14MeV DT neutron measurement systems were installed in 2009 and 2010. Operation and maintenance experience have led to a plan to simplify and upgrade these aging systems to provide a more economical and reliable solution for future DIIID experiments. On simplification, most conventional expensive NIM and CAMAC modules will be removed. Advanced technologies like ultrafast data acquisition and softwarebased pulse identification have been successfully tested. Significant data reduction and efficiency improvement will be achieved by realtime digital pulse identification with a fieldprogrammable gate array. The partly renewed system will consist of 4 neutron counters for absolute calibration and 4 relatively calibrated neutron scintillators covering a wide measurement range. [Preview Abstract] 

GP11.00087: Observations of highly sheared turbulence in the Hmode pedestal using Phase Contrast Imaging on DIIID J.C. Rost, A. Marinoni, E.M. Davis, M. Porkolab, K.H Burrell Highly sheared turbulence with short radial correlation lengths has been measured near the top of the Hmode pedestal, in addition to the previously measured highlysheared turbulence measured in the $E_r$ well. Turbulence in regions of large velocity shear is characterized by radial correlation lengths shorter than the poloidal wavelength ($L < \lambda\sim 2$ cm) and large Dopplershifted frequencies ($f > 200$ kHz). The phase contrast imaging (PCI) diagnostic on DIIID is ideally suited to measuring this density turbulence due to the measurement geometry and high frequency bandwidth. Radial localization is achieved by optical filtering, varying the ExB profile, and shifting the plasma position. Reconfiguration of the $E_r$ well, such as at the LH transition or the transition to wide pedestal QHmode, shows a nearinstantaneous change ($t < 1$ ms) to the sheared turbulence in the $E_r$ well ($\sim 1$ cm inside the separatrix). In contrast, the sheared turbulence near the top of the pedestal ($\sim 2$ cm inside the separatrix) varies over times scales of tens of ms, consistent with pedestal evolution. [Preview Abstract] 

GP11.00088: Increase in turbulent transport at DIIID pedestal top due to RMPinduced reduction of electric field shear Sam Taimourzadeh, Lei Shi, Ihor Holod, Zhihong Lin, Raffi Nazikian, Donald Spong, Andreas Wingen It has been demonstrated that resonant magnetic perturbations (RMPs), applied with the right conditions, suppress or mitigate edge localized modes (ELMs) in DIIID at low, ITERlike, collisionality. Along with the RMP ELM suppression, observations in DIIID, via BES, DBS, and other fluctuation diagnostics, show an increase in electrostatic turbulence near the top of the pedestal, where the mean radial electric field (Er) shearing rate decreases. The Gyrokinetic Toroidal Code (GTC) simulations show that there is a strong correlation between the reduction of the Er shearing rate and an increase in turbulence and transport near the pedestal top of the DIIID shot 158103 during RMP ELM suppression at 03050 ms. A nonlinear outward spreading of the turbulence is observed, which allows a stronger microturbulence on the pedestal top during ELM suppression by RMP. For comparison, the turbulence and transport near the pedestal top remain at low levels when the plasma is ELMing, i.e. when the Er shearing rate is not decreased in the same shot at 03750 ms (ELMing w/ RMP on) and in another shot 158104 at 1350 ms (ELMing without RMP). Furthermore, GTC simulations show that the kink responses to the 3D RMP has little effects on the growth rate of electromagnetic kineticballooning mode and on the turbulent transport and zonal flow damping in electrostatic turbulence$^{\mathrm{1}}$. [Preview Abstract] 

GP11.00089: Installation and Testing of ITER Integrated Modeling and Analysis Suite (IMAS) on DIIID L. Lao, M. Kostuk, O. Meneghini, S. Smith, G. Staebler, R. Kalling, S. Pinches A critical objective of the ITER Integrated Modeling Program is the development of IMAS to support ITER plasma operation and research activities. An IMAS framework has been established based on the earlier work carried out within the EU. It consists of a physics data model and a workflow engine. The data model is capable of representing both simulation and experimental data and is applicable to ITER and other devices. IMAS has been successfully installed on a local DIIID server using a flexible installer capable of managing the core data access tools (Access Layer and Data Dictionary) and optionally the Kepler workflow engine and coupling tools. A general adaptor for OMFIT (a workflow engine) is being built for adaptation of any analysis code to IMAS using a new IMAS universal access layer (UAL) interface developed from an existing OMFIT EU Integrated Tokamak Modeling UAL. Ongoing work includes development of a general adaptor for EFIT and TGLF based on this new UAL that can be readily extended for other physics codes within OMFIT. [Preview Abstract] 

GP11.00090: Neural Network Based Models for Fusion Applications* Orso Meneghini, Arsene Tema Biwole, Teobaldo Luda, Bailey Zywicki, Cristina Rea, Sterling Smith, Phil Snyder, Emily Belli, Gary Staebler, Jeff Canty Whole device modeling, engineering design, experimental planning and control applications demand models that are simultaneously physically accurate and fast. This poster reports on the ongoing effort towards the development and validation of a series of models that leverage neuralnetwork (NN) multidimensional regression techniques to accelerate some of the most mission critical first principle models for the fusion community, such as: the EPED workflow for prediction of the HMode and Super HMode pedestal structure the TGLF and NEO models for the prediction of the turbulent and neoclassical particle, energy and momentum fluxes; and the NEO model for the driftkinetic solution of the bootstrap current. We also applied NNs on DIIID experimental data for disruption prediction and quantifying the effect of RMPs on the pedestal and ELMs. All of these projects were supported by the infrastructure provided by the OMFIT integrated modeling framework. [Preview Abstract] 

GP11.00091: Coupled corepedestal simulations with selfconsistent transport of impurities G. Snoep, O. Meneghini, B. Grierson, A. Ashourvan, E. Belli, J. Candy, P.B. Snyder, G.M. Staebler, J. Citrin, R.J.E. Jaspers This poster reports on the ongoing development of a production tool that robustly predicts density, temperature and rotation profiles from onaxis to the separatrix. The number of free parameters and assumptions in the simulations are reduced by using physics based models that are selfconsistently coupled to one another. Previous coupled corepedestal simulations were shown to be able to reproduce experimental profiles [Meneghini PoP 2016, NF 2017], but relied on prior knowledge of the plasma Z$_{\text{eff}}$ and pedestal rotation boundary condition. Z$_{\text{eff}}$ is an important parameter since it influences both core performance, through transport and line radiation, and pedestal stability via its effect on the bootstrap current. To selfconsistently account for the effects of impurities the previously mentioned corepedestal workflow is iteratively coupled to the 1D impurity transport code STRAHL [Dux 2006] within the OMFIT framework. In this scheme NEO and TGLF will provide the transport fluxes used to calculate the diffusion and pinch profiles used in STRAHL. The new workflow also implements a boundary condition for the plasma rotation based on first principles [StoltzfusDueck PRL 2015]. [Preview Abstract] 

GP11.00092: Uncertainty Propagation in OMFIT Sterling Smith, Orso Meneghini, Choongki Sung A rigorous comparison of power balance fluxes and turbulent model fluxes requires the propagation of uncertainties in the kinetic profiles and their derivatives. Making extensive use of the python uncertainties package, the OMFIT framework has been used to propagate covariant uncertainties to provide an uncertainty in the power balance calculation from the ONETWO code, as well as through the turbulent fluxes calculated by the TGLF code. The covariant uncertainties arise from fitting 1D (constant on flux surface) density and temperature profiles and associated random errors with parameterized functions such as a modified tanh. The power balance and model fluxes can then be compared with quantification of the uncertainties. No effort is made at propagating systematic errors. A case study will be shown for the effects of resonant magnetic perturbations on the kinetic profiles and fluxes at the top of the pedestal. A separate attempt at modeling the random errors with Monte Carlo sampling will be compared to the method of propagating the fitting function parameter covariant uncertainties. [Preview Abstract] 

GP11.00093: Turbulence and sheared flow dynamics during q95 and density scans across the LH transition on DIIID Zheng Yan, George McKee, Punit Gohil, Lothar Schmitz, David Eldon, Brian Grierson, Matt Kriete, Terry Rhodes, Craig Petty Measurements of long wavelength density fluctuation characteristics have been obtained in the edge of Deuterium (D) plasmas across the LH transition on DIIID during density and q95 scans. The relative density fluctuation amplitude measured by Beam Emission Spectroscopy (BES) increases with higher q95. The power threshold is found to increase with plasma current (i.e., lower q95) but with complex density dependence: the largest increase of P$_{\mathrm{LH}}$ is seen at n$_{\mathrm{e}}$\textasciitilde 3.2e19 m$^{\mathrm{3}}$. Interestingly, a dual counterpropagating mode is observed for cases when P$_{\mathrm{LH}}$ is low. The existence of the dual mode is correlated with increasing flow shear. Estimation of the turbulence kinetic energy transfer from turbulence to the flow increases prior to the transition. The complex behaviors of the turbulence characteristics and dual frequency modes interactions impact the flow shear generation, the transition process and the power threshold scaling. [Preview Abstract] 

GP11.00094: LH Transition Dynamics in ITERSimilar D, He, and H Plasmas L. Schmitz, T.L. Rhodes, T. Neiser, L. Zeng, Z. Yan, G.R. McKee, P. Gohil, L. Bardoczi, D. Eldon, C.C. Petty, B. Grierson Recent work at DIIID has revealed important differences in LH transition trigger dynamics between deuterium (D), helium (He) and hydrogen (H) plasmas. The ion flux/polarization current induced by the Reynolds stress is shown to be decisive for the fast time evolution of the edge electric field across the LH transition at intermediate and low plasma density in the plateau collisionality regime, in D and He plasmas. As the corresponding $j\times B_{\mathrm{\thinspace }}$torque increases, concomitant turbulence suppression occurs within 100200 $\mu $s of the peak Reynolds stress gradient. Hplasmas show lower Reynolds stress and \begin{figure}[htbp] \centerline{\includegraphics[width=0.38in,height=0.22in]{130720171.eps}} \label{fig1} \end{figure} torque, and reduced toroidal correlation, of the selforganized \begin{figure}[htbp] \centerline{\includegraphics[width=0.42in,height=0.17in]{130720172.eps}} \label{fig2} \end{figure} edge flow layer, and longer transition times concomitantly with substantially higher required LH transition threshold power. In Hplasmas, the Reynolds force is comparable in magnitude to the neoclassical bulk ion viscosity and the force due to thermal ion orbit loss, potentially explaining the increased power threshold. Supported by the U.S. DOE under DEFC0204ER54698, DEFG0208ER54984, DEAC0209CH11466 and DEFG0208ER54999. [Preview Abstract] 

GP11.00095: Influence of 3D magnetic fields on turbulence at the LH transition and across magnetic islands in DIIID David Kriete, George McKee, Raymond Fonck, David Smith, Zheng Yan, Lucas Morton, Morgan Shafer, Lothar Schmitz Measurements of longwavelength density fluctuations using beam emission spectroscopy (BES) reveal the significant impact of 3D magnetic fields on turbulence amplitudes and characteristics. Fluctuations are measured across an applied static m,n $=$ 2,1 magnetic island that is rotated toroidally through the BES sightlines, providing quasi3D measurement capability. A single unstable broadband turbulence mode is observed near the Opoint, but near the Xpoint, this mode is accompanied by a second mode propagating in the opposite direction; fluctuation amplitudes are also much higher near the Xpoint than the Opoint. 2D fluctuations are also measured in the Lmode edge leading up to LH transitions with applied resonant and nonresonant magnetic perturbations. Normalized fluctuation amplitudes are \textasciitilde 4 times larger with resonant fields than with nonresonant fields. Additionally, dual counterpropagating modes are observed with resonant fields, while only a single mode is observed with nonresonant fields. These measurements may reveal how magnetic perturbations raise the LH power threshold by altering turbulenceflow dynamics leading up to the transition. [Preview Abstract] 

GP11.00096: PhaseSpace Dependence of FastIon Transport by Neoclassical Tearing Modes W Heidbrink, D.J. Lin, Y.B. Zhu, L. Bardoczi, C.S. Collins, C. Muscatello, M. Van Zeeland, G. Kramer, M. Podesta The fastion transport caused by neoclassical tearing modes (NTM) in Hmode plasmas is investigated in different parts of fastion phase space using the newly developed beam modulation technique and a variety of fastion diagnostics that are sensitive to different parts of the distribution function. As measured by electron cyclotron emission, the $(m,n)=(2,1)$ tearing modes have an island width of $\sim10$~cm and change phase $180^\circ$ at the $q=2$ surface. (Here, $m$ is the poloidal mode number and $n$ is the toroidal mode number.) The fast ions are produced by deuterium neutral beam injection at 7581~keV. To measure fastion transport in different parts of phase space, one neutralbeam source is modulated at 20~Hz. Flows in phase space are obtained through comparisons of measured neutron, solidstate neutral particle analyzer, and fastion Dalpha signals with the expected signals in the absence of waveinduced transport. In order to populate different parts of phase space, beams with six different injection geometries are modulated on successive discharges. Initial analysis indicates that the largest transport occurs for onaxis, tangentiallyinjected ions, while smaller transport occurs for offaxis or perpendicular injection. Simulations show similar trends. [Preview Abstract] 

GP11.00097: Orbit Tomography: A Method for Determining the Population of Individual Fastion Orbits from Experimental Measurements L. Stagner, W.W. Heidbrink Due to the complicated nature of the fastion distribution function, diagnostic velocityspace weight functions are used to analyze experimental data. In a technique known as Velocityspace Tomography (VST), velocityspace weight functions are combined with experimental measurements to create a system of linear equations that can be solved. However, VST (which by definition ignores spatial dependencies) is restricted, both by the accuracy of its forward model and also by the availability of spatially overlapping diagnostics. In this work we extend velocityspace weight functions to a full 6D generalized coordinate system and then show how to reduce them to a 3D orbitspace without loss of generality using an actionangle formulation. Furthermore, we show how diagnostic orbitweight functions can be used to infer the full fastion distribution function, i.e. Orbit Tomography. Examples of orbit weights functions for different diagnostics and reconstructions of fastion distributions are shown for DIIID experiments. This work was supported by the U.S. Department of Energy under DEAC0209CH11466 and DEFC0204ER54698. [Preview Abstract] 

GP11.00098: Using Electron Cyclotron Emission Images to localize the drive and damping of Alfv\'en eigenmodes Gerrit Kramer, Ben Tobias, Alan Turnbull, Calvin Domier, Neville Luhmann Alfv\'en Eigenmodes (AE) are routinely imaged in DIIID with the Electron Cyclotron Emission Imaging system (ECEI). From the ECEI images it was found that the AE wave fronts show a clear radial phase variation, which reflects a radial plasma displacement that is induced by the AEs. We use the measured plasma displacement to extract the fluctuating electric and magnetic fields and use these fields to calculate the Poynting flux to determine radial waveinduced energy flows for saturated AEs. These energy flows arise when the drive of the mode does not coincide with the location of the damping of the mode. We will use the measured curved AE wave fronts to determine the radial energy flow that is induced by the AEs and show that the location of fastion drive of the AEs does not coincide with the location of the strongest damping of the mode. [Preview Abstract] 

GP11.00099: Alfven Eigenmode Control in DIIID. W. Hu, E. Olofsson, A. Welander, M. Van Zeeland, C. Collins, W. Heidbrink Alfven eigenmodes (AE) driven by fast ions from neutral beam and ion cyclotron heating are common in present day tokamak plasmas and are expected to be destabilized by alpha particles in future burning plasma experiments. Because these waves have been shown to cause loss and redistribution of fast ions which can impact plasma performance and potentially device integrity, developing control techniques for AEs is of paramount importance. In the DIIID plasma control system, spectral analysis of realtime ECE data is used as a monitor of AE amplitude, frequency, and location. These values are then used for feedback control of the neutral beam power to control Alfven waves and reduce fast ion loss. This work describes tests of AE control experiments in the current ramp up phase, during which multiple Alfven eigenmodes are typically unstable and fast ion confinement is degraded significantly. Comparisons of neutron emission and confined fast ion profiles with and without active AE control will be made. [Preview Abstract] 

GP11.00100: Optimization of DIIID discharges to avoid AE destabilization Jacobo Varela, Donald Spong, Luis Garcia, Juan Huang, Masanori Murakami The aim of the study is to analyze the stability of Alfven Eigenmodes (AE) perturbed by energetic particles (EP) during DIIID operation. We identify the optimal NBI operational regimes that avoid or minimize the negative effects of AE on the device performance. We use the reduced MHD equations to describe the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particles, including the effect of the acoustic modes. We add the Landau damping and resonant destabilization effects using a closure relation. We perform parametric studies of the MHD and AE stability, taking into account the experimental profiles of the thermal plasma and EP, also using a range of values of the energetic particles $\beta$, density and velocity as well the effect of the toroidal couplings. We reproduce the AE activity observed in high poloidal $\beta$ discharge at the pedestal [J. Huang, 58th APS DP/2016] and reverse shear discharges [W. W. Heidbrink, Nucl. Fusion, 53, 093006, (2013)]. [Preview Abstract] 

GP11.00101: Experimental investigation of stability, frequency and toroidal mode number of compressional Alfv\'{e}n eigenmodes in DIIID S Tang, K Thome, D Pace, W.W. Heidbrink, T.A. Carter, N.A. Crocker An experimental investigation of the stability of Dopplershifted cyclotron resonant compressional Alfv\'{e}n eigenmodes (CAE) using the flexible DIIID neutral beams has begun to validate a theoretical understanding and realize the CAE's diagnostic potential. CAEs are excited by energetic ions from neutral beams [Heidbrink, NF 2006], with frequencies and toroidal mode numbers sensitive to the fastion phase space distribution, making them a potentially powerful passive diagnostic. The experiment also contributes to a predictive capability for spherical tokamak temperature profiles, where CAEs may play a role in energy transport [Crocker, NF 2013]. CAE activity was observed using the recently developed Ion Cyclotron Emission diagnostichigh bandwidth edge magnetic sensors sampled at 200 MS/s. Preliminary results show CAEs become unstable in BT ramp discharges below a critical threshold in the range 1.7  1.9 T, with the exact value increasing as density increases. The experiment will be used to validate simulations from relevant codes such as the Hybrid MHD code [Belova, PRL 2015]. [Preview Abstract] 

GP11.00102: Characteristics of Ion Cyclotron Emission on the DIIID Tokamak K.E. Thome, D.C. Pace, R.I. Pinsker, C. del Castillo, Y.B. Zhu, W.W. Heidbrink Understanding the relationship between Ion Cyclotron Emission (ICE) and the energetic particle distribution is important in modernday tokamaks, since passive measurements of ICE in a reactor environment, such as ITER, could provide information on the alpha particle population and fastion losses. ICE is readily excited in DIIID plasmas by kinetic instabilities resulting from neutral beam injection across a wide operational space, including in both helium and deuterium plasmas. A large set of ICE measurements has been collected over the past two years with multiple receiving antennas digitized at 200 Msamples/sec. The fundamental ICE frequency observed in DIIID plasmas is in the 520 MHz range with typical toroidal magnetic fields of 12 T; harmonics are observed up to the Nyquist limit at 100 MHz. These frequencies correspond to both core and edge locations; however, ICE is more often observed at frequencies correlated with ion cyclotron harmonics at the outboard edge. ICE dependencies on plasma and beam parameters such as beam geometry, injection voltage, beam power, plasma density, toroidal field, neutron rate, and ion species are presented. Rapid changes of ICE during ELMs and sawteeth may provide insight into the fast evolution of the beam ion distribution due to these instabilities.~Correlation of the ICE signals with the results of other fastion diagnostics is essential to compare with modelling of underlying kinetic instabilities. [Preview Abstract] 

GP11.00103: Transport of shattered pellet material during fast shutdown of DIIID plasmas D. Shiraki, J.L. Herfindal, L.R. Baylor, N.W. Eidietis, E.M. Hollmann, R.A. Moyer, C.J. Lasnier A second shattered pellet injection (SPI) system has been installed on DIIID, allowing new measurements of radial and toroidal transport of injected impurities during fast shutdown of the plasma. Toroidally separated injections from the two systems vary the impurity profiles and resulting radiative heat loads, relative to available disruption diagnostics. Infrared imaging and radiometry are used to compare heat loads near the injection port with those located toroidally away, in order to quantify radiation asymmetries. Radial transport mechanisms are studied by directing the SPI trajectory away from the magnetic axis in order to reduce the ballistic transport of solid pellet fragments to the core, which more closely matches the ITER injection geometry. The assimilation of this edge deposited SPI is compared to SPI directed towards the core, and also with massive gas injection whose assimilation is strongly dependent on thermal quench MHD mixing. [Preview Abstract] 

GP11.00104: Variation of Argon Impurity Assimilation with Runaway Electron Current in DIIID Eric Hollmann, I. Bykov, R.A. Moyer, D.L. Rudakov, A. Briesemeister, D. Shiraki, J.L. Herfindal, M.E. Austin, C.J. Lasnier, T.N. Carlstrom, N.W. Eidietis, C. PazSoldan, M. van Zeeland Measurements of the effect of runaway electron (RE) pressure upon argon impurity assimilation in DIIID are reported. Intentionally created postdisruption RE beams are ramped to different plasma currents to vary the RE pressure, while impurity levels are varied by injecting argon gas (in addition to Ar already present from the small pellet used to create the disruption). Based on comparisons of current decay rates and hard xray, spectroscopic, interferometer, and Thomson scattering data, it is found that argon is not mixed uniformly through the plasma radially but appears to be preferentially moved out of the center of the plasma toward the walls, relative to the main species (deuterium). This exclusion appears to be stronger at higher plasma current, indicating that this force originates from the runaway electrons. [Preview Abstract] 

GP11.00105: Investigation of runaway electron dissipation in DIIID using a gamma ray imager. A. Lvovskiy, C. PazSoldan, N. Eidietis, D. Pace, D. Taussig We report the findings of a novel gamma ray imager (GRI) to study runaway electron (RE) dissipation in the quiescent regime on the DIIID tokamak. The GRI measures the bremsstrahlung emission by RE providing information on RE energy spectrum and distribution across a poloidal crosssection. It consists of a lead pinhole camera illuminating a matrix of BGO detectors placed in the DIIID midplane. The number of detectors was recently doubled to provide better spatial resolution and additional detector shielding was implemented to reduce uncollimated gamma flux and increase singletonoise ratio. Under varying loop voltage, toroidal magnetic field and plasma density, a nonmonotonic RE distribution function has been revealed as a result of the interplay between electric field, synchrotron radiation and collisional damping. A fraction of the highenergy RE population grows forming a bump at the RE distribution function while synchrotron radiation decreases. A possible destabilizing effect of ParailPogutse instability on the RE population will be also discussed. [Preview Abstract] 

GP11.00106: Simulation of excitation of whistler waves and momentum diffusion of runaway electrons in DIIID tokamak Chang Liu, Eero Hirvijoki, Dylan Brennan, Amitava Bhattacharjee, Guoyong Fu, Donald Spong In recent quiescent runaway electron experiments (QRE) experiments in DIIID, whistler waves excited by runaway electrons have been observed and are found to be associated with the fluctuation of electron cyclotron emission (ECE) signals. To understand this connection and how the whistler instabilities affect the runaway electron distribution in momentum space, a selfconsistent kinetic simulation of runaway electrons, including both the secondary generation and the quasilinear diffusion effects from the excited modes, is conducted. The results show that three different branches of waves can be excited. The low frequency whistler waves and the high frequency magnetized plasma waves are excited by runaway electrons in high energy and low energy regimes respectively, through anomalous Doppler resonance. Due to the close phase velocities of these two branches, the Landau damping of them happens at the same energy regime. These two branches of waves are not observed directly in experiments due to their high frequencies. In addition, we find a third branch of waves with wavevector almost oblique to the magnetic field direction, excited by the bumpontail distribution of the runaway electrons. These waves are in the 100200 MHz frequency range, which agrees with the experimental observations. The cyclic behavior of excitation and damping of whistler waves associated with the fluctuations of ECE signals are also reproduced. [Preview Abstract] 

GP11.00107: Asymmetric SOL Current in Vertically Displaced Plasma J.D. Cabrera, G.A. Navratil, J.M. Hanson Experiments at the DIIID tokamak demonstrate a nonmonotonic relationship between measured scrapeoff layer (SOL) currents and vertical displacement event (VDE) rates with SOL currents becoming largely n=1 dominant as plasma is displaced by the plasma control system (PCS) at faster rates. The DIIID PCS is used to displace the magnetic axis $\sim$10x slower than the intrinsic growth time of similar instabilities in lower singlenull plasmas. Low order (n$\leq$2) mode decomposition is done on toroidally spaced current monitors to attain measures of asymmetry in SOL current. Normalized to peak n=0 response, a 24x increase is seen in peak n=1 response in plasmas displaced by the PCS versus previous VDE instabilities observed when vertical control is disabled. Previous inquiry shows VDE asymmetry characterized by SOL current fraction and geometric parameters of tokamak plasmas[1]. We note that, of plasmas displaced by the PCS, short displacement time scales near the limit of the PCS temporal control appear to result in larger n=1/n=2 asymmetries. [1] Fitzpatrick 2011 Nucl. Fus. 51 053007. [Preview Abstract] 

GP11.00108: Instability Prediction and Disruption Avoidance. A.D. Turnbull, Y.Q. Liu, J.M. Hanson, F. Turco, N.M. Ferraro Disruption avoidance requires both a prediction of the instability proximity and an estimate of the 'disruptability'  the likelihood that the instability will ultimately result in a disruptive event. MHD spectroscopy is a promising option for obtaining information on the proximity of instabilities. Both the direct response and the antenna impedance provide valuable information on the low frequency global normal modes corresponding to stabilized kink modes. Data from DIIID experiments and available nonlinear simulations are used to define quantitative criteria that signify when instabilities ultimately disrupt and when they saturate or dissipate. The key distinction in this approach is the use of physical characteristics of the modes rather than more accessible operation parameters. Simple characteristics of the linear instability for example include the linear growth or damping rate and the mode spatial extent. Criteria can also involve identifying sources of free energy in the nonlinear evolution. [Preview Abstract] 

GP11.00109: Realtime plasma response control for disruption avoidance Jeremy Hanson, Francesca Turco, Gerald Navratil, Nikolas Logan, Edward Strait DIIID experiments demonstrate the viability of using the plasma response to applied nonaxisymmetric perturbations as a realtime control variable for disruption avoidance in lowtorque ITER baseline demonstration discharges. The response to longwavelength, lowfrequency perturbations like the those used here correlates with plasma stability. Consequently, it is sensitive to key parameters that influence stability, increasing with $\beta_N$ and decreasing with plasma rotation. In the experiments, the plasma response amplitude was used to feedback modulate the neutral beam (NB) power, and thereby the plasma stored energy and stability. While the response was being controlled, the NB torque was slowly ramped down, resulting in a decrease in stored energy as the feedback acted to keep the response constant under the changing conditions. A case where the torque was ramped through zero to $$0.5 Nm while maintaining stability was demonstrated, indicating that control can be maintained in the challenging ITERlike parameter regime. [Preview Abstract] 

GP11.00110: Disruption avoidance and fast rampdown techniques for the DIIID experimental scenarios Jayson Barr, N.W. Eidietis, D.A. Humphreys, B. Sammuli, T. Luce Plasma current rampdown in ITER will continue in Hmode from 15 MA to 10 MA, and will keep a diverted shape until termination. This is in contrast to the limited rampdown scenarios typically used in DIIID operations. Additionally, fast emergency rampdown scenarios for ITER and future reactors are a priority for disruption avoidance. New experiments in DIIID use the rampdown phase of a variety of experiments including in the ITER baseline scenario to survey and identify optimized rampdown scenarios for both scheduled terminations and terminations triggered by offnormal event detection. Systematic scans in current ramprate (15 MA/s), neutral beam power (including $\beta_{\mathrm{N}}$ feedback) and rampdown shaping (limited versus continued diverted) have identified fast rampdown scenarios for Lower Single Null (LSN) and Double Null (DN) plasmas. Scenariospecific methods and their rates of successful termination will be presented and compared relative to a historical dataset of rampdown programming in the limiter configuration. Locked modes are found to be the most significant challenge to disruption avoidance in diverted rampdowns. Results for LSN diverted discharges that begin the rampdown with large lockedmodes will also be presented. If available, results of similar experiments on EAST will be presented. [Preview Abstract] 

GP11.00111: Applications of “3D” Magnetic Diagnostics in DIIID E.J. Strait, S. Munaretto, C. PazSoldan, J.M. Hanson, N.C. Logan Measurements of nonaxisymmetric “3D” magnetic fields have been successfully employed in DIIID to validate models of the plasma response to external magnetic perturbations, to validate predictions of the detailed spatial structure of unstable plasma modes, to measure damping rates of stable MHD modes, and to provide input for feedback control of resistive wall modes and of intrinsic error fields. Other possible applications that are ripe for development will be discussed, including the following. External magnetic data allows a direct measurement of the electromagnetic torque exchanged between the plasma and external coils, potentially an indicator of magnetic island onset. “3D” magnetic data in the absence of plasma may be used for direct measurement of error fields caused by coil asymmetries. Spatially resolved realtime measurements of nonaxisymmetric fields can enable early detection of disruption precursors, independent of whether the instability is rotating or stationary. [Preview Abstract] 

GP11.00112: Optimization of 3D Field Design Nikolas Logan, Caoxiang Zhu Recent progress in 3D tokamak modeling is now leveraged to create a conceptual design of new external 3D field coils for the DIIID tokamak. Using the IPEC dominant mode as a target spectrum, the Finding Optimized Coils Using Spacecurves (FOCUS) code optimizes the currents and 3D geometry of multiple coils to maximize the total set's resonant coupling. The optimized coils are individually distorted in space, creating toroidal ``arrays'' containing a variety of shapes that often wrap around a significant poloidal extent of the machine. The generalized perturbed equilibrium code (GPEC) is used to determine optimally efficient spectra for driving total, core, and edge neoclassical toroidal viscosity (NTV) torque and these too provide targets for the optimization of 3D coil designs. These conceptual designs represent a fundamentally new approach to 3D coil design for tokamaks targeting desired plasma physics phenomena. Optimized coil sets based on plasma response theory will be relevant to designs for future reactors or on any active machine. External coils, in particular, must be optimized for reliable and efficient fusion reactor designs. [Preview Abstract] 

GP11.00113: Unlocking locked tearingmode by applied rotating 3D field M. Okabayashi, N. Logan, Z. Wang, Z. Taylor, E. Strait, R. La Haye, J. Hanson, D. Shiraki, S. Inoue Tokamak reactors require control of locked tearing modes. Preemptive applications of a rotating 3D field controlled with (M. Okabayashi: IAEA2016) or without (D. Shiraki: APS/ DPP13/PO4.15) feedback have demonstrated promising paths for recovering Hmode operation even in n$=$1 3D perturbed equilibria. Once a tearing mode becomes deeply locked with nearzero rotation across the radial profile, it is challenging to unlock before disruption. Preliminary observations suggest that the deeply locked state is a configuration with multiple instances of torque bifurcation and internal locking between multiple rational surfaces. Full rotation recovery was found in a narrow range of applied 3D field frequency or after one event of forced reconnection, reflecting the complex transient process of replacing the uncorrected error field with another 3D field. Initial comparison with a nonlinear reduced MHD code (AEOLUSIT) shows qualitative agreement. This work is supported in part by the US Department of Energy under DEAC0209CH11466, DEFG0299ER54531, DESC0003913, and DEFC0204ER54698. [Preview Abstract] 

GP11.00114: Poloidal structure of the plasma response to n=2 perturbations S Munaretto, E.J. Strait, S.R. Haskey, N.C. Logan, C. PazSoldan A study of the plasma response to n=2 resonant magnetic perturbations (RMP) in DIIID plasmas highlights the presence of two dominant modes, in good agreement with predictions from the MHD code MARSQ. The use of RMPs offers potential benefits for nuclear fusion, for example ELM suppression or the correction of error fields, although their effect on the plasma needs to be better understood to predict how best to apply these fields. RMPs with n=2 and variable poloidal spectra are applied in plasma discharges with $q_{95}\sim~4.1$ and $\beta_N \sim 2.2$. Singular value decomposition (SVD) analysis was found to decouple the poloidal structure of the plasma response from the dependence on the spectrum of the perturbation applied. This analysis highlighted the presence of two modes, with the dominant mode peaking at the lowfieldside midplane and the secondary one offmidplane, with indications of the latter being correlated with ELM suppression. The experimental observations are in good agreement with predictions of a dualmode response from MARSQ, improving prospects for projecting optimization of ELM control without triggering deleterious instabilities in future reactors. [Preview Abstract] 

GP11.00115: Demonstration of ECCD Stabilization of m/n$=$\textbf{2/1 NTMs in the Equivalent LowTorque ITER Baseline Scenario in DIIID} Robert La Haye, Edward Strait, KEJ Olofsson, Anders Welander, Jeremy Hanson, Olivier Sauter Experiments in DIIID are studying how best to minimize the average Electron Cyclotron Current Drive power directed at q$=$2 for stabilization of neoclassical tearing modes in discharges with the ITER shape and equivalent lowtorque, low q95\textasciitilde 3.1 and low betaN\textasciitilde 1.8. ITER relies on localized ECCD to stabilize NTMs that would otherwise walllock and lead to disruption. The work contrasts the control strategies of preemption by continuous ECCD at the rational surface (``Active Tracking'') vs. suppression by a pulse of ECCD whenever a growing mode is detected (``Catch {\&} Subdue''). The large rho\textasciitilde 0.75 for q$=$2 and concomitant low Te make the EC current drive relatively weak per MW so that the EC power from 4\textasciitilde 5 wellaligned gyrotrons of 2.5\textasciitilde 2.8 MW, is just marginal for stabilization at about 70{\%} of the neutral beam injection power. The lowtorque makes early mode detection and good initial alignment imperative for prompt suppression before walllocking. Requirements for stabilization will be presented. [Preview Abstract] 

GP11.00116: Ideal kink and neoclassical tearing mode identification in DIIID with ECE Hailin Zhao, Max Austin, Michale Brookman, William Rowan, R.J. La Haye Detection of neoclassical tearing modes (NTMs), which can degrade plasma confinement or cause disruptions, is important in tokamaks. We have developed a code to crosscorrelate ECE/magnetics data to get the amplitude and phase profiles of the electron temperature (Te) oscillation caused by the rotating magnetic island and/or a kink. It has been observed that the $\Delta $Te amplitude on the two sides of the island center can be very different in some discharges. Also, a discrepancy often exists between the location of the rational q surface according to MSEconstrained EFIT and the location of island center according to ECE; this can be an issue for ECCD suppression of NTMs. We explore the possible causes of these two phenomena in terms of ECE location and calibration accuracy. By analyzing the Te fluctuation phase evolution after a large sawtooth crash which triggers an NTM, the presence of a kinklike mode before the onset of NTM can be discerned. Work supported by the US DOE under DEFG0297ER54415 and DEFC0204ER54698. [Preview Abstract] 

GP11.00117: Plasma stability analysis using Consistent Automatic Kinetic Equilibrium reconstruction (CAKE) Matthijs Roelofs, Egemen Kolemen, David Eldon, Alex Glasser, Orso Meneghini, Sterling P. Smith Presented here is the Consistent Automatic Kinetic Equilibrium (CAKE) code. CAKE is being developed to perform realtime kinetic equilibrium reconstruction, aiming to do a reconstruction in less than 100ms. This is achieved by taking, next to realtime Motional Stark Effect (MSE) and magnetics data, realtime Thomson Scattering (TS) and realtime Charge Exchange Recombination (CER, still in development) data in to account. Electron densities and temperature are determined by TS, while ion density and pressures are determined using CER. These form, together with the temperature and density of neutrals, the additional pressure constraints. Extra current constraints are imposed in the core by the MSE diagnostics. The pedestal current density is estimated using Sauters equation for the bootstrap current density. By comparing the behaviour of the ideal MHD perturbed potential energy ($\delta $W) and the linear stability index ($\Delta $') of CAKE to magneticsonly reconstruction, it can be seen that the use of diagnostics to reconstruct the pedestal have a large effect on stability. [Preview Abstract] 

GP11.00118: Detection of plasma stability on DIIID, using the experimentally extracted plasma transfer function based on 3D MHD spectroscopy Zhirui Wang, Nikolas Logan, JongKyu Park, Jonathan Menard, Raffi Nazikian, Stefano Munaretto, Yueqiang Liu, Jeremy Hanson Threedimensional (3D) magnetohydrodynamic (MHD) spectroscopy is successfully applied to extract the plasma transfer function from DIIID experiments. The method uses upper and lower internal coils to perform scans of frequency and poloidal mode spectrum, and measure the corresponding n$=$1 plasma response on 3D magnetic sensors. The transfer function is extracted, based on Pad\'{e} approximation, by fitting the measured signals on different sensors simultaneously. The experimental transfer function not only points out the multimode plasma response but also shows the number of dominant modes and the contribution of each mode to the plasma response. The extracted damping rate of the least stable mode can be a new index indicating plasma stability quantitatively. This method has the potential to optimize ELM suppression and monitor the plasma stability in future fusion reactors. Results and analysis of 3D MHD spectroscopy experiments will be presented. [Preview Abstract] 

GP11.00119: HOHLRAUM AND XRAY CAVITY PHYSICS 

GP11.00120: Development of the Pushered Single Shell Experimental Platform on NIF Jay Salmonson, Eduard Dewald, Frank Graziani, Stephan Maclaren, Jesse Pino, Joseph Ralph, Ryan Sacks, Vladimir Smalyuk, Robert Tipton The goal of the Pushered Single Shell (PSS) experimental campaign is to study mix of partially ionized ablator material into the hotspot. To do this we use a uniformly Si doped plastic capsule, the inner few microns of which can be doped with a few percent Ge. To diagnose mix, we use separated reactants [1]; deuterating the inner Gedoped layer, CD/Ge, while putting Tritium into the Hydrogen capsule fill gas. Mix is then inferred by measuring the neutron yields from DD, DT, and TT reactions. In order to accentuate the cooling of the hotspot due to Bremsstrahlung radiation when Ge is present, we required high hotspot ion temperatures: \textasciitilde 3 keV. This, in turn, requires a fast, symmetric implosion. Using the TwoShock campaign [2] as a starting point, we increased the capsule radius by \textasciitilde 25{\%} to 844 $\mu $m and the peak laser power by over 10{\%} to 475 TW. We also used a low, 0.3 mg/cc, He fill in the hohlraum to maintain control over implosion symmetry. This paper will describe the sequence of keyhole, 1DConA, 2DConA, and Symcap experiments we performed over the last year to tune the PSS implosions. We were successful in achieving our design goals; the PSS is the fastest CH capsule implosion in the laboratory, with peak velocity \textasciitilde 400 $\mu $m, a round hotspot, with hotspot P2 $=$ 0 within errors, and a hotspot ion temperature \textasciitilde 3.5 keV. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DEAC5207NA27344 [1] D.C. Wilson et al. Physics of Plasmas~\textbf{18}, 112707 (2011) [2] S.F. Khan et al. Physics of Plasmas \textbf{23}, 042708 (2016) [Preview Abstract] 

GP11.00121: Rugby and ellipticalshaped hohlraums experiments on the OMEGA laser facility. Veronique Tassin, MarieChristine Monteil, Sylvie Depierreux, PaulEdouard MassonLaborde, Franck Philippe, Patricia Seytor, Pascale Fremerye, Bruno Villette We are pursuing on the OMEGA laser facility indirect drive implosions experiments in gasfilled rugbyshaped hohlraums in preparation for implosion plateforms on LMJ. The question of the precise wall shape of rugby hohlraum has been addressed as part of future megajoulescale ignition designs [1]. Calculations show that ellipticalshaped holhraum is more efficient than sphericalshaped hohlraum. There is less wall hydrodynamics and less absorption for the inner cone, provided a better control of timedependent symmetry swings. In this context, we have conducted a series of experiments on the OMEGA laser facility. The goal of these experiments was therefore to characterize energetics with a complete set of laserplasma interaction measurements and capsule implosion in gasfilled ellipticalshaped hohlraum with comparison with sphericalshaped hohlraum. Experiments results are discussed and compared to FCI2 radiation hydrodynamics simulations. [1] S. Laffite, Physics of Plasmas 17, 102704 (2010). [Preview Abstract] 

GP11.00122: 3D integrated HYDRA simulations of hohlraums including fill tubes* M. M. Marinak, J. Milovich, B. A. Hammel, A. G. MacPhee, V. A. Smalyuk, G. D. Kerbel, S. Sepke, M. V. Patel Measurements of fill tube perturbations from hydro growth radiography (HGR) experiments on the National Ignition Facility show spoke perturbations in the ablator radiating from the base of the tube.$^{\mathrm{1}}$ These correspond to the shadow of the 10 $\mu $m diameter glass fill tube cast by hot spots at early time. We present 3D integrated HYDRA simulations of these experiments which include the fill tube. Meshing techniques are described which were employed to resolve the fill tube structure and associated perturbations in the simulations. We examine the extent to which the specific illumination geometry necessary to accommodate a backlighter in the HGR experiment contributes to the spoke pattern. Simulations presented include high resolution calculations run on the Trinity machine operated by the Alliance for Computing at Extreme Scale (ACES) partnership. 1. A. G. MacPhee, et al., Phys. Rev. E~\textbf{95}, 031204(R) (2017) *This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DEAC5207NA27344 [Preview Abstract] 

GP11.00123: COMPUTATION 

GP11.00124: Abstract Withdrawn We transform the stateofthe art of plasma modeling by taking advantage of novel computational techniques for fast and robust integration of multiscale hybrid (full particle ions, fluid electrons, no displacement current) and fullPIC models. These models are implemented in 3D HYPERS [1] and axisymmetric fullPIC CONPIC [2] codes. HYPERS is a massively parallel, asynchronous code. The HYPERS solver does not step fields and particles synchronously in time but instead executes local variable updates (events) at their selfadaptive rates while preserving fundamental conservation laws. The chargeconserving CONPIC code has a matrixfree explicit finiteelement (FE) solver based on a sparseapproximate inverse (SPAI) algorithm. This explicit solver approximates the inverse FE system matrix (``mass'' matrix) using successive sparsity pattern orders of the original matrix. It does not reduce the set of Maxwell's equations to a vectorwave (curlcurl) equation of second order but instead utilizes the standard coupled firstorder Maxwell's system. We discuss the ability of our codes to accurately and efficiently account for multiscale physical phenomena in 3D magnetized space and laboratory plasmas and axisymmetric vacuum electronic devices. 1. Y.A. Omelchenko and H. Karimabadi, \textit{J. Comp. Phys}. 231,17661780, 2012. 2. DY. Na, Y.A. Omelchenko, H. Moon, BH. Borges, F.L. Teixeira, \textit{J. Comp. Phys}. 346, 295317, 2017. 

GP11.00125: Numerical and experimental analysis of plasma generated on a solid target by a multiMeV electron beam Thierry d'Almeida, Maxime Ribiere, Rémi Maisonny We quantitatively investigate the interaction of a high energy, high flux electron beam with a solid target based on an approach that combines numerical and experimental characterization. The experimental study is carried out diagnosing the interaction of a multiMeV electron beam, delivered by the CEA ASTERIX highpulsed power driver, with an aluminumtantalum target. The numerical analysis builds upon results from ParticleInCell simulations, to reproduce the electron beam dynamics and characteristics, and MonteCarlo simulations, to simulate the interaction of the electron beam with the solid target. The main plasma features emerging from this analysis are analyzed using a 1D radiative transfer model which enabled the experimental spectra to be reproduced numerically with a good consistency. From the numerical integration of the 1D radiative transfer equation, plasma characteristics such as electron temperature and density profiles, as well as ion densities of constitutive species, are determined. [Preview Abstract] 

GP11.00126: On the use of compatible discretizations with the multifluid plasma model Sean Miller, Eric Cyr, John Shadid, Edward Phillips In this presentation, we discuss the advantages and disadvantages of using compatible discretizations in continuous and discontinuous finite element methods for solving the multifluid plasma model. Maxwell’s equations, core components to the multifluid plasma model, are difficult to accurately represent due to the divergence involutions governed by Gauss’ laws. Many methods have been developed to deal with these ‘divergence errors’, notably the generalized Lagrange multiplier methods discussed in Munz et al 2000 and the vector basis discretization approach in Nedelec 1980. While the Lagrange multiplier cleaning schemes are effective and simple to implement, over long time scales the residual errors can have a large influence on the plasma. Compatible discretizations, such as those that represent the electric and magnetic fields on mixed HCurl ‘edge’ elements and HDiv ‘face’ elements, have been shown to be especially useful in the PIC community, however, their implementation can be complex. The goal of this research is to understand the benefits of using some of these divergence handling schemes and compare them in application to finite element methods with both implicit and explicit time integration. [Preview Abstract] 

GP11.00127: Efficient Implicit Plasma Simulation Using Quadrature Moment Inverson David Larson Quadrature moment inversion algorithms [13] are one route to reducing the computational effort required for fully implicit PIC plasma simulation. These algorithms compute a sparse quadrature representation of the velocity distribution from a set of velocity moments. A Jacobianfree Newton Krylov (JFNK) solver can then be used to concurrently solve Maxwell’s equations and the quadrature node equations of motion implicitly differenced in time using the midpoint rule [4], retaining the fully kinetic character of the overall system. The results of several test problems will be presented along with an exploration of routes to achieving convergence of the complete set of PIC particles and field equations. [1] R.O. Fox, J. Comp. Phys. 227 (2008) [2] O. Desjardins, et. al., J. Comp. Phys. 227 (2008) [3] Yuan, C., and R. O. Fox, J. Comp. Phys. 230 (2011) [4] S. Markidis and G. Lapenta, J. Comp. Phys. 230.18 (2011) [Preview Abstract] 

GP11.00128: Reduction of collisionalradiative models for transient, atomic plasmas Richard June Abrantes, Ann Karagozian, David Bilyeu, Hai Le Interactions between plasmas and any radiation field, whether by lasers or plasma emissions, introduce many computational challenges. One of these computational challenges involves resolving the atomic physics, which can influence other physical phenomena in the radiated system. In this work, a collisionalradiative (CR) model with reduction capabilities is developed to capture the atomic physics at a reduced computational cost. Although the model is made with any element in mind, the model is currently supplemented by LANL's argon database\footnote{Argon Atomic Data Sets. https://wwwamdis.iaea.org/LANL/argon/}, which includes the relevant collisional and radiative processes for all of the ionic stages. Using the detailed data set as the true solution, reduction mechanisms in the form of Boltzmann grouping\footnote{Le et al. \textit{Phys. Plasmas} 20, 119 (2013).}, uniform grouping, and quasisteadystate (QSS), are implemented to compare against the true solution. Effects on the transient plasma stemming from the grouping methods are compared. \\ \\ Distribution A: Approved for public release; unlimited distribution, PA (Public Affairs) Clearance Number 17449 [Preview Abstract] 

GP11.00129: A fully implicit, conservative, hybrid kineticion fluidelectron algorithm Adam Stanier, Luis Chacon, Guangye Chen The hybrid model with fullorbit kinetic ions and fluid electrons is a promising approach to describe a wide range of space and laboratory plasmas [e.g. 1]. Explicit hybrid algorithms typically use a predictorcorrector method with subcycling or a semiimplicit field solve to deal with the strict Whistlerwave CFL condition. However, these do not conserve momentum or energy, and are susceptible to numerical instability. While fully implicit methods have been recently explored [2,3] to step over such timescales in a stable manner, these studies have not considered conservation properties. Here, we present a novel particlebased nonlinear hybrid algorithm that features discrete conservation of mass, momentum, energy and the solenoidal condition of the magnetic field. The scheme combines fully implicit time advance with orbitaveraging of the ion particles and the flexibility of conservative smoothing to reduce numerical noise. We verify the algorithm for a number of test problems and demonstrate the unique conservation properties. \\\\ 1. A. Stanier, et. al., {\it Phys. Plasmas} {\bf 24}, 022124 (2017).\\ 2. B. Sturdevant, et. al., {\it J. Comput. Phys.} {\bf 316}, 519 (2016). \\ 3. J. Cheng, et. al., {\it J. Comput. Phys.} {\bf 245}, 364 (2013). [Preview Abstract] 

GP11.00130: Metriplectic Gyrokinetics and Discretization Methods for the Landau Collision Integral Eero Hirvijoki, Joshua W. Burby, Michael Kraus We present two important results for the kinetic theory and numerical simulation of warm plasmas: 1) We provide a metriplectic formulation of collisional electrostatic gyrokinetics that is fully consistent with the First and Second Laws of Thermodynamics. 2) We provide a metriplectic temporal and velocityspace discretization for the particle phasespace Landau collision integral that satisfies the conservation of energy, momentum, and particle densities to machine precision, as well as guarantees the existence of numerical Htheorem. The properties are demonstrated algebraically. These two result have important implications: 1) Numerical methods addressing the VlasovMaxwellLandau system of equations, or its reduced gyrokinetic versions, should start from a metriplectic formulation to preserve the fundamental physical principles also at the discrete level. 2) The plasma physics community should search for a metriplectic reduction theory that would serve a similar purpose as the existing Lagrangian and Hamiltonian reduction theories do in gyrokinetics. The discovery of metriplectic formulation of collisional electrostatic gyrokinetics is strong evidence in favor of such theory and, if uncovered, the theory would be invaluable in constructing reduced plasma models. [Preview Abstract] 

GP11.00131: Variational principle for the parallelsymplectic representation of electromagnetic gyrokinetic theory Alain Brizard The nonlinear (full$f$) electromagnetic gyrokinetic VlasovMaxwell equations are derived in the parallelsymplectic representation from an Eulerian gyrokinetic variational principle. The gyrokinetic VlasovMaxwell equations are shown to possess an exact energy conservation law, which is derived by Noether method from the gyrokinetic variational principle. Here, the gyrocenter Poisson bracket and the gyrocenter Jacobian contain contributions from the perturbed magnetic field. In the full$f$ formulation of the gyrokinetic VlasovMaxwell theory presented here, the gyrocenter parallelAmp\`{e}re equation contains a secondorder contribution to the gyrocenter current density that is derived from the secondorder gyrocenter ponderomotive Hamiltonian. [Preview Abstract] 

GP11.00132: A domaindecomposed multimodel plasma simulation of collisionless magnetic reconnection I. A. M. Datta, U. Shumlak, A. Ho, S. T. Miller Collisionless magnetic reconnection is a process relevant to many areas of plasma physics in which energy stored in magnetic fields within highly conductive plasmas is rapidly converted into kinetic and thermal energy. Both in natural phenomena such as solar flares and terrestrial aurora as well as in magnetic confinement fusion experiments, the reconnection process is observed on timescales much shorter than those predicted by a resistive MHD model. As a result, this topic is an active area of research in which plasma models with varying fidelity have been tested in order to understand the proper physics explaining the reconnection process. In this research, a hybrid multimodel simulation employing the HallMHD and twofluid plasma models on a decomposed domain is used to study this problem. The simulation is set up using the WARPXM code developed at the University of Washington, which uses a discontinuous Galerkin RungeKutta finite element algorithm and implements boundary conditions between models in the domain to couple their variable sets. The goal of the current work is to determine the parameter regimes most appropriate for each model to maintain sufficient physical fidelity over the whole domain while minimizing computational expense. [Preview Abstract] 

GP11.00133: Hybrid plasma model simulations of a plasma opening switch Andrew Ho, U. Shumlak, I. A. M. Datta 
(Author Not Attending)

GP11.00134: Abstract Withdrawn Numerical studies of the validity of the guidingcenter approximation are performed with the code {\sf ASCOT} [1] through a careful analysis of the fullorbit and guidingcenterorbit trajectories of nonrelativistic and relativistic charged particles moving in axisymmetric and nonaxisymmetric magneticfield geometries. The validity of the guidingcenter approximation is also investigated through the exact analytical solution for the motion of a charged particle in a straight nonuniform magnetic field with a constant field gradient [2]. \newline \noindent [1] E.~Hirvijoki, {\it et al.}, Comput.~Phys.~Commun.~{\bf 185}, 1310 (2014). \newline \noindent [2] A.~J.~Brizard, Phys.~Plasmas {\bf 24}, 042115 (2017). 

GP11.00135: The UPSF code: a metaprogrammingbased highperformance automatically parallelized plasma simulation framework Xiatian Gao, Xiaogang Wang, Binhao Jiang UPSF (Universal Plasma Simulation Framework) is a new plasma simulation code designed for maximum flexibility by using edgecutting techniques supported by C++17 standard. Through use of metaprogramming technique, UPSF provides arbitrary dimensional data structures and methods to support various kinds of plasma simulation models, like, Vlasov, particle in cell (PIC), fluid, FokkerPlanck, and their variants and hybrid methods. Through C++ metaprogramming technique, a single code can be used to arbitrary dimensional systems with no loss of performance. UPSF can also automatically parallelize the distributed data structure and accelerate matrix and tensor operations by BLAS. A threedimensional particle in cell code is developed based on UPSF. Two test cases, Landau damping and Weibel instability for electrostatic and electromagnetic situation respectively, are presented to show the validation and performance of the UPSF code. [Preview Abstract] 

GP11.00136: Exact collisional moments for plasma fluid theories David Pfefferle, Eero Hirvijoki, Manasvi Lingam The velocityspace moments of the often troublesome nonlinear Landau collision operator are expressed exactly in terms of multiindex Hermitepolynomial moments of the distribution functions. The collisional moments are shown to be generated by derivatives of two wellknown functions, namely the RosenbluthMacDonaldJuddTrubnikov potentials for a Gaussian distribution. The resulting formula has a nonlinear dependency on the relative mean flow of the colliding species normalised to the rootmeansquare of the corresponding thermal velocities, and a bilinear dependency on densities and higherorder velocity moments of the distribution functions, with no restriction on temperature, flow or mass ratio of the species. The result can be applied to both the classic transport theory of plasmas, that relies on the ChapmanEnskog method, as well as to deriving collisional fluid equations that follow Grad's moment approach. As an illustrative example, we provide the collisional tenmoment equations with exact conservation laws for momentum and energytransfer rate. [Preview Abstract] 

GP11.00137: Finding the crossover from phase mixing to collisions with an integral transform. J. M. Heninger, P. J. Morrison The onedimensional linearized VlasovPoisson system can be exactly solved using the ``G transform'' [1], an integral transform based on the Hilbert transform. This transform removes the electric field, leaving a simple advection equation. We investigate how this integral transform interacts with the FokkerPlanck collision operator. The commutator of this collision operator with the G transform (the ``shielding term'') is shown to be negligible. We exactly solve the advectiondiffusion equation without the shielding term. This solution determines when collisions dominate and when advection (i.e. Landau damping) dominates. Introducing an energy source term that balances the energy lost to dissipation allows for the creation of a steady state distribution function that transfers energy from larger to smaller velocity scales via Landau damping. Unlike the Kolmogorov cascade, this is an energy cascade that occurs completely in velocity space: there is no nonlinearity and the spatial dependence is trivial. We hope that the G transform will be used to simplify gyrokinetic codes or other kinetic models. [1] P. Morrison and D. Pfirsch, Phys Fluids B 4, 3038 (1992); P. Morrison Trans. Theo. Stat. Phys. 29, 397 (2000). [Preview Abstract] 

GP11.00138: Implementation of parallel moment equations in NIMROD Hankyu Q. Lee, Eric D. Held, JeongYoung Ji As collisionality is low (the Knudsen number is large) in many plasma applications, kinetic effects become important, particularly in parallel dynamics for magnetized plasmas. Fluid models can capture some kinetic effects when integral parallel closures are adopted. The adiabatic and linear approximations are used in solving general moment equations\footnote{J.Y. Ji and E. D. Held, Phys. Plasmas 15, 102101 (2008).} to obtain the integral closures. In this work, we present an effort to incorporate nonadiabatic (timedependent) and nonlinear effects into parallel closures. Instead of analytically solving the approximate moment system, we implement exact parallel moment equations in the NIMROD fluid code. The moment code is expected to provide a natural convergence scheme by increasing the number of moments. [Preview Abstract] 

GP11.00139: Generalized approach to variational and Hamiltonian kineticMaxwell plasma theory. Cesare Tronci, Alexander Close Hamiltonian and variational techniques have proved particularly helpful for constructing new kinetic and hybrid plasma models. Here, we present a geometric construction that relates these approaches for a generalized kineticMaxwell theory, producing Lagrangian and Eulerian variants. We then present a particular specialization, in which the wellknown MaxwellVlasov theory is shown to emerge under appropriate choices of symplectic form and energy function. [Preview Abstract] 

GP11.00140: Hybrid driftkinetic pressure coupling scheme from a variational principle. Alexander Close, Cesare Tronci A hybridkinetic pressure coupling scheme (PCS) model is presented in the lowgyrofrequency approximation. This fully energyconserving model is derived from variations of a Lagrangian over a semidirect product manifold, and produces important terms in the Vlasov equation that correct models previously appearing in the literature. [Preview Abstract] 

GP11.00141: Beatification: Flattening Poisson brackets for plasma theory and computation P. J. Morrison, T. F. Viscondi, I. Caldas A perturbative method called beatification$^{\dagger}$ is presented for producing nonlinear Hamiltonian fluid and plasma theories. Plasma Hamiltonian theories, fluid and kinetic, are naturally described in terms of noncanonical variables. The beatification procedure amounts to finding a transformation that removes the explicit variable dependence from a noncanonical Poisson bracket and replaces it with a fixed dependence on a chosen state in the phase space. As such, beatification is a major step toward casting the Hamiltonian system in its canonical form, thus enabling or facilitating the use of analytical and numerical techniques that require or favor a representation in terms of canonical, or beatified, Hamiltonian variables. Examples will be given. \\ $\dagger$ P.~J.~Morrison and J.~Vanneste, Ann.~Phys.~{\bf 368}, 117 (2016); T.~F.~Viscondi, I.~L.~Caldas, and P.~J.~Morrison, Phys.~Plasmas {\bf24}, 032102 (2017); J.\ Phys.~A {\bf49}, 165501 (2016). [Preview Abstract] 

GP11.00142: Nonlinear saturation of the ITG instability with fully kinetic ions Matthew Miecnikowski, Benjamin Sturdevant, Yang Chen, Scott Parker We study the growth and saturation of the iontemperaturegradient (ITG) instability in simulations with fully kinetic ions and adiabatic electrons. The ion trajectories are integrated using the full Lorentz force, fully resolving the cyclotron motion and capturing the corresponding finite Larmor radius effects. In slab geometry, the linear growth and nonlinear saturation characteristics show good agreement with analogous gyrokinetic simulations across a wide range of parameters, and the fully kinetic simulation correctly reproduces the nonlinearly generated zonal flow. We discuss our progress on the extension of this model to toroidal geometry to study more realistic turbulence. This work represents an important step towards the extension of kinetic modeling of plasma turbulence to regimes where the gyrokinetic ordering is violated or the gyrokinetic equations are questioned. [Preview Abstract] 

GP11.00143: Stabilization approach for an explicit hybrid particleincell method for bridging multiple timescales Rinat Khaziev, Shane Keniley, Davide Curreli Fullykinetic ParticleinCell (PiC) simulations of magnetized plasma sheaths including electrons, plasma ions, and heavy material impurities remain a big challenge because of the large discrepancy between the mass of the light species and that of the heavy species. The timescales required for such simulations span over multiple orders of magnitude, from picoseconds for the electron dynamics, to microseconds for heavyion transport across the sheath. In this work, we analyze a numerical approach applicable to explicit PiC schemes that iterates between a fullykinetic representation of the electrons and a reduced electron model; the method allows to capture fullykinetic effects at time scales relevant to heavyion transport. A frequency analysis of the approach reveals the strategy required for stable operation of the method and prevent unstable driftlike behavior in the phase space. The method has been applied to plasma sheath simulations with oblique magnetic fields. In order to highlight the benefits of the method, the moments of the distribution function are compared to both longtime fullykinetic PiC simulations, and to PiC simulations with only a reduced electron model. Finally, comparisons with a continuum BoltzmannPoisson code solving the same problem are reported. [Preview Abstract] 

GP11.00144: Opensource Framework for Storing and Manipulation of Plasma Chemical Reaction Data T. G. Jenkins, S. N. Averkin, J. R. Cary, S. E. Kruger We present a new opensource framework for storage and manipulation of plasma chemical reaction data that has emerged from our inhouse project MUNCHKIN. This framework consists of python scripts and C$++$ programs. It stores data in an SQL data base for fast retrieval and manipulation. For example, it is possible to fit crosssection data into most widely used analytical expressions, calculate reaction rates for Maxwellian distribution functions of colliding particles, and fit them into different analytical expressions. Another important feature of this framework is the ability to calculate transport properties based on the crosssection data and supplied distribution functions. In addition, this framework allows the export of chemical reaction descriptions in LaTeX format for ease of inclusion in scientific papers. With the help of this framework it is possible to generate corresponding VSim (ParticleInCell simulation code) and USim (unstructured multifluid code) input blocks with appropriate crosssections. [Preview Abstract] 

GP11.00145: A OneStep Variational Guiding Center Integrator using Toroidal Regularization C Leland Ellison, Joshua Burby Guiding center and gyrocenter particle advances  central to test particle, driftkinetic, and gyrokinetic simulations  stand to benefit from symplectic integration techniques, which have had a profound impact in other physics disciplines. The noncanonical Hamiltonian formulation of these systems has kept such symplectic integration thus far elusive, except for in restricted magnetic geometries or by using computationally expensive transformations to canonical coordinates. In this work, we perform a nearidentity Lie transformation to the guiding center coordinates to obtain a ``toroidally regularized'' Lagrangian for which symplectic integration can be more readily achieved. This transformation also eliminates the effective magnetic field appearing in the denominator of the guiding center equations and correspondingly eliminates the large parallel velocity singularities from the equations. The recently developed technique of degenerate variational integration is then applied to the regularized Lagrangian to obtain a onestep variational integrator valid for any magnetic geometry with nonzero toroidal magnetic field. [Preview Abstract] 

GP11.00146: A PICKSC Science Gateway for enabling the common plasma physicist to run kinetic software Q. Hu, B. J. Winjum, A. Zonca, C. Youn, F. S. Tsung, W. B. Mori Computer simulations offer tremendous opportunities for studying plasmas, ranging from simulations for students that illuminate fundamental educational concepts to researchlevel simulations that advance scientific knowledge. Nevertheless, there is a significant hurdle to using simulation tools. Users must navigate codes and software libraries, determine how to wrangle output into meaningful plots, and oftentimes confront a significant cyberinfrastructure with powerful computational resources. Science gateways offer a Webbased environment to run simulations without needing to learn or manage the underlying software and computing cyberinfrastructure. We discuss our progress on creating a Science Gateway for the ParticleinCell and Kinetic Simulation Software Center that enables users to easily run and analyze kinetic simulations with our software. We envision that this technology could benefit a wide range of plasma physicists, both in the use of our simulation tools as well as in its adaptation for running other plasma simulation software. [Preview Abstract] 

GP11.00147: The ParticleinCell and Kinetic Simulation Software Center W. B. Mori, V. K. Decyk, A. Tableman, R. A. Fonseca, F. S. Tsung, Q. Hu, B. J. Winjum, W. An, T. N. Dalichaouch, A. Davidson, L. Hildebrand, A. Joglekar, J. May, K. Miller, M. Touati, X. L. Xu The UCLA ParticleinCell and Kinetic Simulation Software Center (PICKSC) aims to support an international community of PIC and plasma kinetic software developers, users, and educators; to increase the use of this software for accelerating the rate of scientific discovery; and to be a repository of knowledge and history for PIC. We discuss progress towards making available and documenting illustrative opensource software programs and distinct production programs; developing and comparing different PIC algorithms; coordinating the development of resources for the educational use of kinetic software; and the outcomes of our first sponsored OSIRIS users workshop. We also welcome input and discussion from anyone interested in using or developing kinetic software, in obtaining access to our codes, in collaborating, in sharing their own software, or in commenting on how PICKSC can better serve the DPP community. [Preview Abstract] 

GP11.00148: PlasmaPy: initial development of a Python package for plasma physics Nicholas Murphy, Andrew Leonard, YiMin Huang, Colby Haggerty We report on initial development of PlasmaPy: an open source communitydriven Python package for plasma physics [1]. PlasmaPy seeks to provide core functionality that is needed for the formation of a fully open source Python ecosystem for plasma physics. PlasmaPy prioritizes code readability, consistency, and maintainability while using best practices for scientific computing such as version control, continuous integration testing, embedding documentation in code, and code review. We discuss our current and planned capabilities, including features presently under development. The development roadmap includes features such as fluid and particle simulation capabilities, a GradShafranov solver, a dispersion relation solver, atomic data retrieval methods, and tools to analyze simulations and experiments. We describe several ways to contribute to PlasmaPy. PlasmaPy has a code of conduct and is being developed under a BSD license, with a version 0.1 release planned for 2018. The success of PlasmaPy depends on active community involvement, so anyone interested in contributing to this project should contact the authors. [1] The code repository is at https://github.com/PlasmaPy/PlasmaPy [Preview Abstract] 

GP11.00149: Exact Energy and Momentum Conservation in Variational MacroParticle Plasma Models B. A. Shadwick, Timothy Kawamoto, M. Perin We consider a class of variational macroparticle plasma models that exhibit simultaneous conservation of energy and momentum. These models retain translation invariance by using a Fourier representation of the electromagnetic fields in place of a spatial grid. That is, the Fourier amplitudes of the fields are the fundamental quantities. From the discrete Lagrangian, a canonical Hamiltonian system is obtained in the usual way, for which we introduce a symplectic integrator. We present a general formulation of the method with examples drawn from 11/2D studies of intense laserplasma interactions. We comment on the relative merits of the Lagrangian vs. Hamiltonian formulations and discuss efficiency and practicality of using this technique in three dimensions. [Preview Abstract] 

GP11.00150: A Computational Model for Predicting Gas Breakdown Zachary Gill Pulsedinductive discharges are a common method of producing a plasma. They provide a mechanism for quickly and efficiently generating a large volume of plasma for rapid use and are seen in applications including propulsion, fusion power, and highpower lasers. However, some common designs see a delayed response time due to the plasma forming when the magnitude of the magnetic field in the thruster is at a minimum. New designs are difficult to evaluate due to the amount of time needed to construct a new geometry and the high monetary cost of changing the power generation circuit. To more quickly evaluate new designs and better understand the shortcomings of existing designs, a computational model is developed. This model uses a modified singleelectron model as the basis for a Mathematica code to determine how the energy distribution in a system changes with regards to time and location. By analyzing this energy distribution, the approximate time and location of initial plasma breakdown can be predicted. The results from this code are then compared to existing data to show its validity and shortcomings. [Preview Abstract] 

GP11.00151: GPU Acceleration of ParticleInCell Methods Benjamin Cowan, Sergey Averkin, John Cary, Jarrod Leddy, Scott Sides, Gregory Werner Graphics processing units (GPUs) have become key components in many supercomputing systems, as they can provide more computations relative to their cost and power consumption than conventional processors. However, to take full advantage of this capability, they require a strict programming model which involves singleinstruction multipledata execution as well as significant constraints on memory access. To bring the full power of GPUs to bear on plasma physics problems, we must adapt the computational methods to this new programming model. We have developed a GPU implementation of the particleincell (PIC) method, one of the mainstays of plasma physics simulation. This framework is highly general and enables advanced PIC features such as high order particles and absorbing boundary conditions. The main elements of the PIC loop, including field interpolation and particle deposition, are designed to optimize memory access. We describe recent progress in these algorithms, including arbitrary grid types and multiple GPUs per node. [Preview Abstract] 

GP11.00152: Recent Performance Results of VPIC on Trinity W. D. Nystrom, B. Bergen, R. F. Bird, K. J. Bowers, W. S. Daughton, F. Guo, A. Le, H. Li, H. Nam, X. Pang, D. J. Stark, W. N. Rust III, L. Yin, B. J. Albright Trinity is a new DOE compute resource now in production at Los Alamos National Laboratory. Trinity has several new and unique features including two compute partitions, one with dual socket Intel Haswell Xeon compute nodes and one with Intel Knights Landing (KNL) Xeon Phi compute nodes, use of on package high bandwidth memory (HBM) for KNL nodes, ability to configure KNL nodes with respect to HBM model and on die network topology in a variety of operational modes at run time, and use of solid state storage via burst buffer technology to reduce time required to perform I/O. An effort is in progress to optimize VPIC\footnote{K. J. Bowers, B. J. Albright, L. Yin, B. Bergen, and T. J. T. Kwan, Phys. Plasmas 15, 055703 (2008)} on Trinity by taking advantage of these new architectural features. Results of work will be presented on performance of VPIC on Haswell and KNL partitions for single node runs and runs at scale. Results include use of burst buffers at scale to optimize I/O, comparison of strategies for using MPI and threads, performance benefits using HBM and effectiveness of using intrinsics for vectorization. [Preview Abstract] 

GP11.00153: A threedimensional particleincell simulation of the diocotron instability for cylindrical geometry Young Hyun Jo, Vladimir V. Mikhailenko, Vladimir S. Mikhailenko, Hae June Lee In a nonneutral plasma like an electron beam under a magnetic field, the diocotron instability can occur with a shear in the flow velocity of surface waves, which is a type of KelvinHelmholtz instability in principle. Recently, there has been advanced theories that explain the evolution of the diocotron instability using nonmodal analysis considering shearing modes. In a previous study, a twodimensional particleincell simulation was performed for verification of the theory with an initially loaded cylindrical annular plasma column surrounded by a conducting boundary. The growth rates of the diocotron instability measured in the simulation agree well with the theory. As an extension of the previous work, we have extended the model to a threedimensional cylindrical particleincell simulation and compared the results with those of the twodimensional simulation. In addition, the effect of the particle flows in the axial direction has been investigated. [Preview Abstract] 

GP11.00154: An Approach to Radiation Hydrodynamics Within a Generalized Continuum Mixture Theory Jim Reynolds, Gabrielle Miller, Melvin Baer, Shane Schumacher Mixed material cells have long posed challenges for radiation hydrodynamic treatments in multiphysics codes. Baer and Nunziato [1] developed a twophase mixture formulation which is recently expanded by Baer and Schumacher to a generalized model. We present an extension to this generalized continuum mixture theory by this model incorporating energybased\sout{ }gray\sout{ }radiation diffusion in a multicomponent fluid. The extended model is presented along with a numerical approach including verification examples. [1] Baer, M.R. and Nunziato, J.W., Int. J. Multiphase Flow, Volume 12, No. 6 1986 [Preview Abstract] 

GP11.00155: KEEN Wave Simulations: Comparing various PIC to various fixed grid Vlasov to PhaseSpace Adaptive Sparse Tiling {\&} Effective Lagrangian (PASTEL) Techniques Bedros Afeyan, David Larson, Bradley Shadwick, Richard Sydora We compare various ways of solving the VlasovPoisson and VlasovMaxwell equations on rather demanding nonlinear kinetic phenomena associated with KEEN and KEEPN waves. KEEN stands for Kinetic, Electrostatic, Electron Nonlinear, and KEEPN, for electronpositron or pair plasmas analogs. Because these selforganized phase space structures are not steadystate, or single mode, or fluid or low order moment equation limited, typical techniques with low resolution or too much noise will distort the answer too much, too soon, and fail. This will be shown via Penrose criteria triggers for instability at the formation stage as well as particle orbit statistics in fully formed KEEN waves and KEENKEEN and KEENEPW interacting states. We will argue that PASTEL is a viable alternative to traditional methods with reasonable chances of success in higher dimensions. [Preview Abstract] 

GP11.00156: Code Modernization of VPIC Robert Bird, David Nystrom, Brian Albright The ability of scientific simulations to effectively deliver performant computation is increasingly being challenged by successive generations of highperformance computing architectures. Code development to support efficient computation on these modern architectures is both expensive, and highly complex; if it is approached without due care, it may also not be directly transferable between subsequent hardware generations. Previous works have discussed techniques to support the process of adapting a legacy code for modern hardware generations, but despite the breakthroughs in the areas of miniapp development, portableperformance, and cache oblivious algorithms the problem still remains largely unsolved. In this work we demonstrate how a focus on platform agnostic modern codedevelopment can be applied to ParticleinCell (PIC) simulations to facilitate effective scientific delivery. This work builds directly on our previous work optimizing VPIC, in which we replaced intrinsic based vectorisation with compile generated autovectorization to improve the performance and portability of VPIC. In this work we present the use of a specialized SIMD queue for processing some particle operations, and also preview a GPU capable OpenMP variant of VPIC. Finally we include a lessons learnt s [Preview Abstract] 

GP11.00157: Evaluation of tungsten effect on CFETR phase I performance Shengyu Shi, Xiang Jian, Vincent S. Chan, Nan Shi, Guoqiang LI, Xiang Gao An integrated modeling workflow using OMFIT/TGYRO is constructed to evaluate Tungsten (W) impurity effects on China Fusion Engineering Test Reactor (CFETR) performance. Selfconsistent modeling of W core density profile, accounting for both turbulence and neoclassical transport contribution, is performed based on the CFETR steadystate scenario developed by D.Zhao (ZhaoDeng, APS, 2016). It's found that the fusion performance degraded in a limited level with increasing W concentration. The main challenge arises in sustainment of Hmode with significant W radiation. Assuming the power threshold of HL back transition is approximately the same as that of LH transition; it is found that the W concentration is not allowed to exceed 3e5 to stay in Hmode for CFETR phase I according to the scaling law found by Takizuka (Takizuka etc, Plasma Phys. Control Fusion, 2004). In addition, it's found that the tolerance of W concentration decreases with increasing pedestal density by tradeoff study of pedestal density and temperature. A future step is to connect this requirement to W wall erosion modeling. [Preview Abstract] 
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