Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session VP14: Poster Session: Magnetic Confinement: Turbulence & Transport (2:00pm  5:00pm)On Demand

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VP14.00001: Study of Electron Heat Transport in Positive and Negative Triangularity Shaped Discharges in DIIID using Perturbative Experiments Ruifeng Xie, Max Austin, Alessandro Marinoni Plasma shaping, in particular triangularity ($\delta$), has been shown to influence turbulence levels and energy confinement in experimental tokamak plasmas. The effects of triangularity on electron heat transport in DIIID have been studied using modulated electron cyclotron heating (ECH) deposited at $\rho\approx 0.35$. The experimental electron temperature data from electron cyclotron emission (ECE) diagnostics are Fourier analyzed. The resulting phase and amplitude from multiple harmonics are compared with an analytical model to infer diffusive and convective transport coefficients. The results are then compared with global transport calculations from ONETWO. It has been observed that, in matched Lmode negative (NT) and positive (PT) trangularity experiments, NT plasmas have on average slower heat pulse propagation and reduced electron thermal energy transport. Consequently, this analysis clearly demonstrates the improved confinement obtained in Lmode NT discharges. [Preview Abstract] 

VP14.00002: A Model For The Poloidal Angle Dependence Of The Saturated Potential Fluctuation Spectrum Of Flux Tube Gyrokinetic Turbulence Simulations Gary Staebler, Jeff Candy, Nicola Bonanomi The time average intensity of electric potential fluctuations from a gyrokinetic turbulence simulation in tokamak geometry is three dimensional in space: the Fourier transform spectrum, of poloidal ($k_y$) and radial ($k_x$) wavenumbers, and the poloidal angle ($\theta$). Examination of the poloidal variation of the intensity spectrum shows that there is always a peak at zero radial wavenumber ($k_x=0$). The spectrum of the zonal potential ($k_y=0$) is found to be almost independent of the poloidal angle and symmetric in $k_x$. Away from the outboard midplane there is a second peak at the zero of the local total radial wavenumber $k_r=k_x+k_y \hat{s} \theta$. The second peak location depends upon the sign of the poloidal angle and is not periodic. A model of both peaks added together provides a reasonable fit to the 3D spectrum if the poloidal variation of the magnetic field and radial gradient metric are taken into account. An overall Gaussian envelope is needed to fit the poloidal variation of the intensity peaks. This envelope is close to the envelope of the most unstable linear eigenmode at each poloidal wavenumber. The application of these results to the TGLF quasilinear transport model will be discussed. [Preview Abstract] 

VP14.00003: On the feasibility of $\mathbf{T_i}$ collisional heating and $\mathbf{T_e/T_i}$ control on DEMO using ECRH Guillermo Suarez Lopez, Emiliano Fable, Emanuele Poli, Giovanni Tardini, Hartmut Zohm We explore the physical feasibility of a DEMO1 scenario supplied uniquely with Electron Cyclotron Resonant Heating (ECRH) as the external heating and currentdrive system. Specifically, we study the ability of ECRH to collisionally heat a deuteriumtritium mixture from Lmode to Hmode, while controlling the $T_e/T_i$ ratio, crucial for the onset of ITG turbulent transport. Simulations with the ASTRA code [1] employing the TGLF code [2] as the turbulent transport model, are used to assess the kinetic profile temporal evolution of such a DEMO1 discharge. Boundary conditions at the plasma edge are applied to model the transition from the initial Lmode to Hmode flat top, including the treatment of the Hmode pedestal. Numerical scans over the position and width of the ECRH deposition layer, ECRH available power and plasma density Greenwald fraction are performed. For each scan, a power balance analysis is made with regards to collisional heating from electrons to ions, electron and ion heat fluxes and $T_e/T_i$ ratio temporal evolution. The results and conclusions drawn from such scans will be presented at the conference.\\ \, [1] G. V. Pereverzev et al. Tech. rep. 5/98. MaxPlanckInstitut fur Plasmaphysik, 2002.\\ \, [2] G. M. Staebler et al., In: Physics of Plasmas 12.10 (2005) [Preview Abstract] 

VP14.00004: Effects of plasma parameters on temperature and density pedestals in ITER scenarios T. Rafiq, J. Weiland, E. Schuster ITER temperature and density pedestals are computed using Weiland anomalous transport model. The neoclassical transport is calculated using NCLASS or ChangHinton model. The effects of plasma parameters on electron temperature, electron density and ion temperature pedestal height and width are computed. The current density, magnetic field strength, edge density fueling, neoclassical ion diffusivity, alpha heating, and flow shear are varied. The simulations are started with prescribed sources and a guessed Lmode profile and evolve to LH transition and temperature and density pedestal selfconsistently. There are no assumptions in the simulations that suggest that there will be an LH transition or where the temperature and density barrier should be. An L to H mode transition can be obtained by either stabilization due to pressure gradient driven shear flow or diamagnetic effects. The goal of these integrated ITER simulations is to investigate the sensitivity of fusion power production in ITER to the height of the density and temperature pedestal. [Preview Abstract] 

VP14.00005: Electromagnetic plasma turbulence driven by electrontemperature gradient Toby Adkins, Alexander Schekochihin, Colin Roach, Plamen Ivanov A simplified local model of a tokamak plasma is derived in the lowbeta limit of gyrokinetics in a slab of constant magnetic field curvature and gradient. The ordering adopted was chosen in order to retain Alfv\'{e}nic perturbations to the magnetic field, while ordering out compressive perturbations, in a similar manner to [A. Zocco and A.A. Schekochihin, \textit{Physics of Plasmas }\textbf{18}, 102309 (2011)]. It is shown that in the electromagnetic regime, isobaric KineticAlfv\'{e}n waves can become unstable to the curvaturedriven ETG instability, driving turbulence on scales above the electron skin depth. Assuming critical balance [M. Barnes et al., \textit{Phys. Rev. Lett. }\textbf{107, }115003 (2011)], it is shown that the resultant turbulent heat flux is proportional to the temperature gradient, driving transport that is less stiff than the conventional ETG picture. The structure of the underlying electromagnetic ETG instability is characterized. [Preview Abstract] 

VP14.00006: Compressional Magnetic Fluctuations in Global Gyrokinetics ShuWei Tsao, M.J. Pueschel, Anna Tenerani, David Hatch Compressional magnetic field fluctuations are commonly ignored in gyrokinetic simulations. They tend not to have a large effect in core fusion plasmas, but may affect electromagnetic modes in the tokamak pedestal, the reconnection physics active in the solar corona, or the LAPD high$\beta$ experiments. [Pueschel et al., PoP 22, 062105 (2015)]. The radially global gyrokinetic framework including compressional fluctuations is derived. Its implementation in the gyrokinetic turbulence code \textsc{Gene} is then compared against local fluxtube scenarios of a standard tokamak benchmark case, at LAPD high$\beta$ experimental parameters, and for magnetic reconnection in 3D coronal loop geometry. Due to the usage of finiteelement radial base function, the magnetic potential in the two directions perpendicular to the background magnetic field should be computed separately. This decouples the $B_\parallel$ from its gyroaveraged quantity $\bar{B}_\parallel$, thus a new gyroaverage procedure for the compressional magnetic field is also implemented. [Preview Abstract] 

VP14.00007: A FokkerPlanck collision model for gyrokinetic simulations in stellarators Alexander von Boetticher, Michael Barnes We describe an implementation of the gyrokinetic linearised FokkerPlanck collision operator that satisfies pertinent conservation laws and is valid at arbitrary collisionalities. The differential testparticle component of the operator is exact; the implementation of the integrodifferential fieldparticle component relies on the spherical harmonic and Laguerre polynomial expansion introduced by Hirshman and Sigmar [S. P. Hirshman, D. J. Sigmar, Phys. Fluids $\bf{19}$, 1532 (1976)]. Properties and numerical methods of the implementation in the $\delta f$gyrokinetic code $\texttt{stella}$ [M. Barnes, F. I. Parra, M. Landreman, arXiv:1806.02162] are discussed, and benchmarks against the collision model of the gyrokinetic solver GS2 are provided. Preliminary results of collisional gyrokinetic simulations of microinstabilities in the Wendelstein7X stellarator are also presented. [Preview Abstract] 

VP14.00008: ETG Turbulence Isotropization Stefan Tirkas, Haotian Chen, Gabriele Merlo, Scott Parker Electron temperature gradient (ETG) instabilities drive electronscale turbulence in tokamak plasmas. This turbulence is characterized in gyrokinetic simulations by anisotropic "streamers" which persist into the saturated turbulent state and produce experimentally relevant energy transport [1]. On the other hand, simple fluid models [2] show that the ExB nonlinearity causes rotation in kspace and results in isotropic spectra. These qualitative features are demonstrated using the gyrokinetic code GENE running in the ETG regime, and in a 2D pseudospectral HasegawaMimatype ETG model initiated with streamers. We plan to compare to nonlinear, toroidal, gyrokinetic theory and analysis of what experimental regimes lead to streamers and substantial electron heat transport. We also provide evidence of spontaneous zonal flow generation in GENE, which will be shown by the aforementioned theory to be a result of a modulation instability involving the unstable ETG modes. [1] W. Dorland, et al., Phys. Rev. Lett. 85 5579 (2000) [2] P. W. Terry, W. Horton, Phys. Fluids 26 106 (1983) [Preview Abstract] 

VP14.00009: Statistical Analysis on Particle Confinement of Hydrogenic Ions in Large Helical Device Naoto IMAGAWA, Hiroshi Yamada, Tatsuya Yokoyama, Katsumi Ida, Ryuichi Sakamoto, Keisuke Fujii, Mikirou Yoshinuma, Gen Motojima, Kenji Tanaka Particle transport in NBI and ECH heated plasmas has been investigated on Large Helical Device (LHD). The control of hydrogenic isotope concentration, i.e, tritium and deuterium (D) is a critical issue to maximize fusion power output. Recently, D plasma experiment has begun in LHD, and measurement separating hydrogen (H) and D density profiles has become available by bulk charge exchange recombination spectroscopy (bCXRS). Global particle confinement time in steady state has been compared for H, D and H/D mixture plasmas in order to characterize the isotope effect on particle transport. It has been found that the global particle confinement time deteriorates from H to D. The transient decay time of H/D ratio after H and D pellet injection has been also analyzed. In contrast to global particle confinement time, significant difference of the decay time between H and D particles has not been recognized. [Preview Abstract] 

VP14.00010: Automated Analysis of Turbulent Electron Temperature Fluctuation Measurements at ASDEX Upgrade Christian Yoo, Rachel Bielajew, Garrard Conway, Pedro Molina Cabrera, Pablo RodriguezFernandez, Anne White Turbulence is known to be responsible for anomalous transport in tokamaks, reducing energy confinement times and limiting reactor performance. The correlation electron cyclotron emission (CECE) diagnostic installed on the ASDEX Upgrade tokamak measures broadband, longwavelength electron temperature fluctuations, yielding insight into turbulencedriven transport. Automated analysis of CECE data is difficult due to the presence of artifacts stemming from various operating conditions that can obscure the turbulent temperature fluctuations. Here we present preliminary results of an automated computational method that accounts for these artifacts. We create a logicbased algorithm to detect artifactcausing factors and flag affected data. We then implement a machinelearning algorithm to quantify the resulting variation of measurements. These capabilities will enhance the versatility of the CECE diagnostic, enabling it to contribute to our understanding of turbulence and transport in a wider range of tokamak operating conditions. [Preview Abstract] 

VP14.00011: Global microinstabilities in stellarators with radial electric field Michael Cole, Toseo Moritaka, David Gates, Robert Hager, ChoongSeock Chang Recent experimental results have shown that heat loss in optimized stellarators can be dominated by turbulent transport. The global gyrokinetic code XGC has been extended to model this physics, in analogy to extensive gyrokinetic studies of turbulence in tokamaks. Unlike in tokamaks, the radial electric field, set by neoclassical transport, is a key factor for predicting turbulence. For example, mode localisation, which is observed to be strong in many optimized stellarators, can be drastically altered by the radial electric field. The position of the mode, when combined with geometric properties such as the curvature, can be key in determining linear growth rates and, we suggest, saturated turbulence amplitudes. The XGC code has been extended to include such effects, capable of taking analytical estimates for the radial electric field as well data produced by selfconsistent calculations with neoclassical transport codes. XGC takes stellarator geometry information from the VMEC or HINT3D codes. In this presentation, we show how the inclusion of the radial electric field modifies earlier simulations of microinstabilities in stellarators. Simulations of LHDlike configurations will be compared to a quasiaxisymmetric configuration. [Preview Abstract] 

VP14.00012: End Losses from a Magnetic Mirror: Kinetic Simulations and Guiding Center Theory Ari Le, Jan Egedal, Cary Forest, Bill Daughton, Adam Stanier Recent advances in hightemperature superconducting coil technology and very promising results from an experimental magnetic mirror machine [1] have renewed interest in magnetic mirror confinement concepts, and a new mirror device is being built at the University of WisconsinMadison. Using a set of kinetic simulations in the LANL particleincell code VPIC [2], we study end losses from a magnetic mirror in the GasDynamic Trap (GDT) [3] regime. GDT confinement depends sensitively on plasma collisions, which allow a thermalized population to develop in the GDT’s central cell. We present 2D kinetic simulations including Coulomb collisions and injection of beams highenergy, lowcollisionality “sloshing” fuel ions. The density profiles, electric field, heat losses, and particle distributions produced in the simulations agree favorably with a guiding center theory for the electrons and ions in the GDT exhaust. [1] P.A. Bagryansky et al., Physical review letters, 114, 205001 (2015). [2] K. J. Bowers, et al., Physics of Plasmas, 15, 055703 (2008). [3] V.V. Mirnov and D.D. Ryutov, Pis' ma v Zhurnal Tekhnicheskoj Fiziki, 5, 678682 (1979). [Preview Abstract] 

VP14.00013: Reconstructing NBIdriven rotation profiles with the local gyrokinetic code GS2 N. Christen, M. Barnes, H. Weisen, P. Siren Neutral beam injection (NBI) is used in tokamaks as a heating mechanism and as a drive for toroidal rotation. Previous work established that sheared toroidal flows, such as those produced by NBI, can substantially affect radial turbulent transport \footnote{M Artun and W M Tang \textbf{Phys. Fluids B}, 4(5):11021114, 1992} \footnote{M Barnes et al. \textbf{Phys. Rev. Lett.}, 106:175004, 2011}. Larger experiments like ITER are expected to rely on NBI operating at higher energies, which implies additional engineering challenges, and a lower ratio of torque to beam power. However, there is little work based on first principles to quantify how such beams affect transport. We present a procedure giving insights on how NBI determines the plasma rotation. This method hinges on local, deltaf gyrokinetic simulations, with a novel algorithm for flow shear implemented in the GS2 code \footnote{M Kotschenreuther et al. \textbf{Comput. Phys. Commun.}, 88(2):128140, 1995}. We validate our approach against experiments carried out at the JET facility. Our simulations show that linear instabilities in the presence of flow shear can change significantly when radial wavelengths (typically of the order of the ion gyroradius) also include electron gyroradius scales. [Preview Abstract] 

VP14.00014: Substance of neoclassical transport under resonant magnetic perturbations in tokamaks JongKyu Park, SangKyeun Kim, Nikolas Logan, Stanislas Pamela, Marina Becoulet, SeongMoo Yang, YongSu Na A resonant magnetic perturbation (RMP) offers a promising pathway to control MHD instabilities in tokamaks. A difficulty in addressing underlying RMP transport is due to the potential mixture of integrable and nonintegrable field lines across which the neoclassical framework becomes incompatible. It is shown, in various alternative approaches, that it is critical to take both radial and insurface displacements of the field lines into account to precisely quantify the nonambipolar (NA) transport contributions. An example is the coupling between a nonlinear JOREK MHD response and GPEC transport simulations, which has been recently successful in improving the prediction of RMPdriven torque as well as particle pumping in KSTAR to some degree. The neoclassical part of particle or heat transport is predicted to be small in this study as typically expected but should not be generally ignored in RMP applications. The NA particle transport can reach to an anomalous level locally in the region where particle and collisional rates are both low. The rapid diffusion of the hot and collisionless particles can also elevate the NA heat transport to an alarming level, pointing to the importance of the predictive RMP optimization in highperformance tokamak scenarios. [Preview Abstract] 

VP14.00015: Transport studies using general parallel moment equations in NIMROD Hankyu Lee, J.Andrew Spencer, Eric Held, JeongYoung Ji The general parallel moment equations are obtained by taking velocity moments of the first order drift kinetic equation. The infinite set is then truncated at a certain number of equations to be solved. By including more moments in the set of equations, obtained closure relations become more accurate at lower collisionality. In this work, the parallel moment equations, as implemented in NIMROD code, are solved to calculate closures for axisymmetric, neoclassical transport. These closures may also be used in general fluid simulations. The bootstrap current and plasma flows are calculated from the closures for various tokamak equilibria. Results are compared with continuum kinetic calculations in NIMROD. [Preview Abstract] 

VP14.00016: Transport comparison of ASDEX Upgrade and Wendelstein 7X ECRH hydrogen plasmas Evan Scott, Benedikt Geiger, Marc Beurskens, Gregor Birkenmeier, Emiliano Fable, Golo Fuchert, Joachim Geiger, Ulrich Stroth, Yuriy Turkin, Gavin Weir Turbulenceinduced heat transport is a challenging field of study in fusion energy science due to inherently complex and nonlinear behavior. Here, the heat transport in electron cyclotronheated hydrogen plasmas has been compared between the ASDEX Upgrade (AUG) tokamak and the Wendelstein 7X (W7X) stellarator using the ASTRA code to shed light on the effect of magnetic configuration on transport. While the electron heat diffusivity $\chi_e$ is comparable between AUG Lmode and W7X plasmas when the input heating power is scaled to the plasma surface area, the ion heat diffusivity $\chi_i$ is lower in W7X at midradius by a factor of 3 or greater. This is also seen when the analysis is performed using matched AUG and W7X density and temperature profiles. This may be indicative of the $1/R$ dependence of interchange turbulence or reduced turbulent transport in the 3D magnetic field structure of W7X. [Preview Abstract] 

VP14.00017: Regimes of weak ITG/TEM for transport barriers without velocity shear Michael Kotschenreuther, X. Liu, D. R. Hatch, S. M. Mahajan, M. J. Pueschel, M. Halfmoon, M. Zarnstorff, A. Garofalo, J. McClenaghan, I. J. McKinney, J. Qian, S. Ding, C. Giroud, J. C. Hillesheim, C. F. Maggi, S. Saarelma, X. Chen We show there exists a regime where coupled ITG/TEM modes are hugely weakened enabling Transport Barriers (TB). The passage to this regime has arisen in TBs in multiple experimental contexts: ITB in DIIID, JET, W7X and EAST, Hmode pedestals on DIIID and JET, and likely very many others. We examine representative cases of these. A distinguishing and crucial feature of the analysis is that the regime is understood in terms of general concepts of nonequilibrium thermodynamics. A constraint founded in momentum conservation limits fluctuations that try to maximize entropy production, and so enables steep gradients in TBs. A very large number of linear and nonlinear gyrokinetic simulations with GENE are used, in controlled scans, and for experimental cases, with novel analytic tools to understand this regime and its underlying cause. The proposed National Compact Stellarator device gives especially favorable results. [Preview Abstract] 

VP14.00018: Influence of plasma turbulence on tokamak selfdriven current Weixing Wang, E. Startsev, M. G. Yoo, S. Ethier, J. Chen, T. S. Hahm Steady state tokamak operation relies on fully noninductive current for generating the poloidal magnetic field needed for plasma confinement, the majority of which is from plasma selfdriven current. The selfdriven current also strongly affects key MHD instabilities, such as NTM and ELM. Plasma turbulence due to various ubiquitous microinstabilities can drive substantial macroscopic plasma current which presents a new pathway to affect tokamak confinement and global stability. The underlying process closely links to turbulence driven momentum transport and flow generation. This study focuses on the quantitative identification of distinct effects, namely, turbulence acceleration, parallel Reynolds stress and fluctuationinduced scattering and detrapping, on current generation at different regimes. It is showed that the size and amplitude of residual stress driven current profile corrugation sensitively depend on qprofile structure. The strong current corrugation at weak magnetic share can drive a seed island for NTM at rational magnetic surfaces. On the other hand, fluctuationinduced effective collisions may considerably reduce the plasma selfdriven current in low collisionality regime relevant to high temperature burning plasmas. [Preview Abstract] 

VP14.00019: The Coreedge Coupling of the ParticleinCell Gyrokinetic Codes GEM and XGC Junyi Cheng, Julien Dominski, Yang Chen, ChoongSeock Chang, SeungHoe Ku, Robert Hager, Scott Parker Within the Exascale Computing Program (ECP), the HighFidelity Whole Device Modeling (WDM) project aims at delivering a firstprinciplebased computational tool that simulates the plasma neoclassical and turbulence plasma dynamics from the core to the edge of a tokamak. To permit such simulations, the two existing particleincell (PIC) gyrokinetic codes GEM and XGC are coupled together, where GEM is optimized for the core and XGC is optimized for the edge plasma. Due to the different grids, a mapping technique is developed for transferring the information between GEM's structured and XGC's unstructured meshes. Coupling with adiabatic electrons has been achieved with a spatial coupling scheme [1], and tested for the cyclonebasedcase (CBC) equilibrium and for a DIIID like plasma. A new coupling scheme with kinetic electrons, in which the particle distribution function is exchanged on a 5D grid, is being developed and progress will be reported. [1] J. Dominski, et al. Physics of Plasmas 25 (7), 072308 [Preview Abstract] 

VP14.00020: Gyrokinetic analysis of global highbeta MHD eqiulibria Rahul Gaur, William Dorland, I. G. Abel, Dylan Langone, Pierre Gourdain To build high power density, compact, fusion devices one possibility is to use very high beta equilibria. These have previously been studied in the context of MHD stability (Hsu, Artun and Cowley PoP 3,266 (1996)). We wish to look at their transport and confinement properties. To this end, we present a linear gyrokinetic stability analysis of highbeta, updownsymmetric, global MHD equilibria. These equilibria were obtained using the asymptotic methods of Hsu et al. We investigate the effects of the five good properties of these equilibria mentioned by Hsu et al: reduced trapped particle fraction, strongly stabilising average curvature, short connection lengths in the bad curvature region, intense local magnetic shear and locallyfavourable gradB drifts. [Preview Abstract] 

VP14.00021: Totalf extension of an electromagnetic gyrokinetic algorithm in mixedvariable formulation Robert Hager, SeungHoe Ku, M. D. J. Cole, Amil Sharma, Alexey Mishchenko, C.S. Chang Numerical studies [e.g. D. Hatch et al., Nuclear Fusion 57, 036020 (2017)] suggest that electromagnetic effects on microturbulent transport could be relevant in tokamak edge plasma and impact the height and shape of the Hmode pedestal. For simulation of these phenomena in realistic geometry including the pedestal, scrapeoff layer and divertor plates, we extend the deltaf electromagnetic gyrokinetic algorithm in mixedvariable formulation [A. Mishchenko et al., Phys. Plasmas 21, 052113 (2014)] implemented in XGC to a totalf formulation. We discuss the numerical implementation, performance, and scalability of this algorithm as well as results of verification exercises. Results of studies applying this new algorithm are presented separately by S. Ku (for EM effect on divertor heatload width), and A. Sharma (for highbeta, highly shaped NSTX plasma). [Preview Abstract] 

VP14.00022: Improved Forward Modeling of Impurity Transport With Integration of STRAHL and EMC3EIRENE Colin Swee, Thomas Wegner, Fernando Castillo, Heinke Frerichs, Benedikt Geiger Understanding of impurity transport properties in fusion plasmas is important since accumulation of heavy impurities can lead to radiation losses and thus,degradation of plasma conditions. One common method for studying impurity transport utilizes the controlled injection of impurities using laser ablation. Upon injection, these impurities emit characteristic line radiation in the UV and XRay spectra. Measured emissivities are then compared with synthetic data from modeling tools such as the 1D impurity transport code, STRAHL. However, when using the currently utilized codes, complications arise when trying to consider stellarators featuring complicated 3D ﬁeld structures. Particularly, the scrapeoﬀlayer, often featuring island structures and open ﬁeld lines, cannot be modeled by a 1D code. Thus, improved forward modeling requires more careful consideration in the SOL region. This work describes the initial results from a combination of STRAHL with the 3D transport code EMC3Eirene. EMC3Eirene provides the analysis with information on the SOL impurity transport and neutral density, while also providing self consistent proﬁles for the electron and ion temperatures. The impact of coupling these two codes is presented for selected HSX and W7X experiments. [Preview Abstract] 

VP14.00023: Saturation of Pedestal Electron Temperature Gradient Turbulence Justin Walker, David Hatch In Hmode tokamak plasmas, edge transport barriers facilitate better plasma confinement. A key question is the nature of the residual turbulent transport at play in the steep gradient region of the pedestal. Electron temperature gradient (ETG) driven turbulence is a major mechanism for electron heat transport in the pedestal. Here we present a study of these instabilities and their basic saturation properties in the nonlinear regime. Results from gyrokinetic simulations of electron temperature gradient instability (ETG) will be presented. Several branches of ETG modes coexist in the pedestal, often at the same wavenumbers. The role of these mode branches in the nonlinear turbulence will be discussed. In contrast to core plasmas, the nonlinear phase of the system has fewer characteristics of the most unstable linear mode and saturates via an inverse cascade of energy. Implications for quasilinear transport modeling will be discussed. [Preview Abstract] 

VP14.00024: Electromagnetic simulation of stronglyshaped, highbeta NSTX plasma with the gyrokinetic code XGC A. Y. Sharma, M. D. J. Cole, B. J. Sturdevant, A. Mishchenko, S. Ku, R. Hager, C. S. Chang, W. Guttenfelder, S. M. Kaye The explicit electromagnetic (EM) version [Cole et al., in preparation] of the global gyrokinetic particleincell code XGC is used to study global electromagnetic instabilities in NSTX shot 132588, which features strong shaping at high plasma beta. We identify the dominant modes that are present under these conditions and investigate their effect on plasma transport and, in particular, the electron thermal transport. The explicit EM gyrokinetic implementation uses the Hamiltonian formulation of EM gyrokinetics, and has thus far successfully mitigated an associated numerical cancellation problem via a combination of the pullback scheme [Mishchenko et al., PoP, 2014] and an adjustable control variate method, even for the extreme case of NSTX shot 132588, despite the severity of this problem increasing with plasma beta and with the complexity of the magnetic geometry. A fullyimplicit EM gyrokinetic scheme is also implemented in XGC. This scheme uses the symplectic formulation of EM gyrokinetics, for which the cancellation problem is absent, and accelerates the implicit numerical scheme with a fluid preconditioner [Chen and Chacon, CPC, 2015]. Basic verification results are presented for this scheme, including the wellknown global intercode benchmark of [Gorler et al., PoP, 2016]. [Preview Abstract] 
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