Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session CO5: Core and Edge Transport 
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Chair: Paul Terry, University of Wisconsin, Madison Room: OCC B113114 
Monday, November 5, 2018 2:00PM  2:12PM 
CO5.00001: Twofluid edgeplasma SOL turbulent transport driven by interchange/tearing instabilities Wendell Horton, Linjin Zheng, Miura Hideaki Twofluid numerical nonlinear simulations of interchange/tearing instabilities in a 2D slab for edge plasma are carried out. The current diffusivity model describes the effects of the stochastic magnetic field linesformedin the simulations. Current diffusivity develops to enforce a lowlevel saturated current profile in the SOL region as well as a current jump across the Last Closed Flux Surface (LCFS). plasma outside theLCFS is on open magnetic fields terminating on the divertor plates. Earlier singlefluid MHD simulations have shown that interchange modes transform into tearing modes forming mixed currentinterchange tearing modes. New simulations show how the steep edge plasma massdensity gradients bring in twocomponent FLRHall MHD effects that limit the turbulence level. We carry out twodimensional simulations with the twofluid (Hall) term and the gyroviscous term. The extended FLRHallMHD model brings about enhanced plasma flows, including diamagnetic flows, and reduces the saturation level of the turbulence while mixing the influence of the currentinterchange tearing modes. H. Miura, L.Zheng, W. Horton,“Numerical simulations of interchange/tearing instabilities in 2D slab with a numerical model for edge plasma”, Phys. of Plasmas 24, 092111 (2017) . 
Monday, November 5, 2018 2:12PM  2:24PM 
CO5.00002: Pedestal Turbulence: Microtearing in the Presence of RMPs M.J. Pueschel, D.R. Hatch, M. Kotschenreuther, X. Liu, S. Mahajan, P.W. Terry, Z.R. Williams One of the key turbulence regimes in presentday tokamak pedestals is driven by the microtearing (MT) instability, allowing density and temperature profiles to evolve independently, thus distinguishing it from MHDlike regimes, where profiles are coupled. Based on the identification of quasicoherent modes on DIIID as signatures of MT turbulence, we investigate by means of nonlinear gyrokinetic simulations the impact of external resonant magnetic perturbations (RMPs) on this regime, applying a constantintime perturbation at the experimentally relevant length scale. We separate the dynamical impact on the MT from the islandinduced flutter. Results are compared to scenarios where RMPs interact with electrostatic modes, in particular trappedelectron mode turbulence. 
(Author Not Attending)

CO5.00003: Theoretical explanations of Imode impurity removal and Hmode poloidal pedestal asymmetries Silvia Espinosa, Peter J Catto Usage of highz wall materials switches the fusion challenge from heat handling to impurity removal. I propose the first method of measuring the radial impurity flux from available diagnostics. Hmode was discovered 35 years ago to quadruple fusion power, and later explained by turbulence reduction by sheared flows. A decade ago, Imode operation was discovered to have the same property, while removing impurities and providing free fueling. Thanks to the measuring method developed, I explain the outward radial impurity flux without invoking a sometimes undetected turbulent mode. This is supported by the observed E×B flow shear, whch also explains the desired energy confinement via turbulence reduction. Stronger poloidal asymmetries than predicted by the most comprehensive neoclassical models have been measured, calling into question the reduction of turbulence in Hmode tokamak pedestals. I have developed the first selfconsistent theoretical model retaining the impurity diamagnetic flow and the twodimensional radial flow features. It successfully explains collisionally the experimental inout asymmetries; thus making them consistent with Hmode pedestal turbulence reduction. 
Monday, November 5, 2018 2:36PM  2:48PM 
CO5.00004: Gyrokinetic Landau collision operator in conservative form Qingjiang Pan, Darin R Ernst A gyrokinetic linearized exact (not model) Landau collision operator is derived by transforming the symmetric and conservative Landau form. The formulation obtains the velocity space current density and preserves the conservative form as the divergence of this current density. The operator contains both testparticle and fieldparticle contributions, and finite gyroradius effects are evaluated in either Bessel function series or gyrophase integrals. While equivalent to the gyrokinetic FokkerPlanck form with the Rosenbluth potentials [B. Li and D. R. Ernst, Phys. Rev. Lett. 106, 195002 (2011)], the gyrokinetic Landau form explicitly preserves the symmetry between testparticle and fieldparticle contributions, thus automatically satisfies the conservation laws and Htheorem. The operator in conservative form is being implemented in the gyrokinetic GENE code with a finitevolume method that preserves the discrete conservation laws. The gyrophase integrals for finite gyroradius effects can be precomputed with an adaptive integration program. While model field terms may conserve the first three velocity moments, their local effects in velocity space have little connection with the exact Landau operator, altering classical transport. 
Monday, November 5, 2018 2:48PM  3:00PM 
CO5.00005: Global gyrokinetic simulations of Alfvén modes in ITER plasmas. Alberto Bottino, Thomas HaywardSchneider, Alessandro Biancalani, Roman Hatzky, Alexey Mishchenko, Philipp Lauber The global gyrokinetic code ORB5 [S. Jolliet et al., Comp. Phys. Comm., 177, 409 (2007)] can simultaneously include electromagnetic perturbations, shaped MHD axisymmetric equilibria, zonalflow preserving sources, collisions, and the ability to solve the full core plasma including the magnetic axis. Multiple ion species are described by gyrokinetic equations, while a driftkinetic model is generally used for the electrons. Recently, the algorithm of the electromagnetic solver has been rewritten, based on the socalled mixedvariable formulation of the gyrokinetic theory [A. Mishchenko et al., Phys. Plasmas 21, 052113 (2014)]. The resulting code allows for significantly larger time steps even for experimentally relevant conditions. It has been applied to different Alfénic physics problems and verified against other existing codes. In this work, we focus on the role of Alfvén instabilities, driven unstable by an energetic particle population, in the standard ITER 15MA scenario (highbeta equilibrium) with realistic density and temperature profiles for thermal ions, electrons and energetic particles. The results obtained by those costly global simulations are particularly valuable for the validation of simpler analytical or hybridkinetic models. 
Monday, November 5, 2018 3:00PM  3:12PM 
CO5.00006: Verification and Validation of Integrated Simulation of Energetic Particles in Toroidal Plasmas Zhihong Lin Gyrokinetic simulations of energetic particles (EP) interactions with thermal plasmas focus on the DIIID discharge #159243, which is a NBIheated plasma with many smallamplitude reversed shear Alfven eigenmodes (RSAE) and toroidal Alfven eigenmodes (TAE), significant flattening of the EP profile, and large amplitude microturbulence. GTC linear simulations using EFIT equilibrium and experimental profiles find that the most unstable AE is RSAE with significant growth rate for toroidal mode number n=36. The most unstable RSAE is n=4 and has a radial domain of ⍴=0.3  0.6 (squareroot of normalized toroidal flux function). These results are in good agreement with other gyrokinetic and gyrokinetic MHDhybrid codes, as well as experimental data. Consistent with experimental observation, GTC simulations also find that weaker TAE exists at the outer radial domain of ⍴=0.6  0.9. Finally, GTC simulations find strong driftwave instability excited by thermal plasma pressure gradients in the core. The linear ITGlike mode amplitude peak at ⍴=0.3, but large fluctuations nonlinearly spread to the whole radial domain. These results indicate that RSAE and TAE in this DIIID experiment could interact nonlinear with each other and with the microturbulence. 
Monday, November 5, 2018 3:12PM  3:24PM 
CO5.00007: Investigation of Multiscale Turbulence in DIIID ITER Baseline Discharges Nathan T Howard, Christopher G Holland, Terry L Rhodes, Anne Elisabeth White, Jeff Candy, Martin J Greenwald, George Mckee The role of ionscale (ITG/TEM) and electronscale (highk TEM/ETG) turbulence and their coupling in reactorrelevant conditions has been investigated in DIIID ITER baseline discharges. Dedicated experiments used localized ECH to stimulate conditions exhibiting crossscale coupling and a suite of turbulence diagnostics (BES, DBS, PCI) were employed to provide an ideal test bed for understanding crossscale coupling and for validating gyrokinetic simulation. Changes in profiles which favor crossscale coupling and possible density fluctuation signatures were documented in the wavenumber spectrum of intermediatek (k*rho_{s} ~ 2.55.0) fluctuations measured with DBS. Ion, electron, and multiscale gyrokinetic simulations using the CGYRO code were performed using all experimental inputs. Single scale simulations reveal that lowk turbulence cannot explain experimental electron heat fluxes, but that inclusion of highk will likely resolve this discrepancy. Comparison of simulated and measured spectra, ion and electron heat fluxes, and impurity transport will be presented as part of an ongoing effort to validate the gyrokinetic model and to understand the nature of crossscale coupling in reactor relevant conditions. 
Monday, November 5, 2018 3:24PM  3:36PM 
CO5.00008: Nonlinear Saturation of Kinetic Ballooning Modes by Zonal Fields in Toroidal Plasmas Ge Dong, Amitava Bhattacharjee, Zhihong Lin, Jian Bao The nonlinear evolution of the kinetic ballooning modes (KBM) has been a subject of great interest for eruptive phenomena in space and fusion plasmas. While the nonlinear evolution of ballooning modes has been proposed as a mechanism for detonation in tokamak plasmas, the role of kinetic effects in such nonlinear dynamics remains largely unexplored. In this work, global gyrokinetic PIC simulation results of nonlinear KBM are presented for the cyclone base case with plasma beta ranging from 1.5% (near KBM marginality) to 2% (strong KBM instability). We find that instead of detonating, the nonlinear KBM continues to grow exponentially in an "intermediate" regime, followed by nonlinear saturation regulated by spontaneously generated zonal fields. The origin of the zonal fields can be attributed to threewave coupling processes. In the intermediate regime, localized current sheets develop that are prone to secondary tearing instabilities, but the growth rate of the resistive tearing instabilities appear to be subdominant to KBM growth. Additional simulation results using DIIID pedestal equilibrium with unstable KBM show the same saturation mechanism. 
Monday, November 5, 2018 3:36PM  3:48PM 
CO5.00009: Roles of turbulence and E×B flow shear during nonlocal transport on the HL2A tokamak Zhongbing Shi In this work, nonlocal experiments with repetitive supersonic molecular beam injection (SMBI) have been carried out on the HL2A tokamak. The plasma rotation and turbulent structures during nonlocal response are reported by a multichannel Doppler backscattering reflectometer. The correlations of the turbulent structures, plasma rotation and their association with the strength of the nonlocal effect are studied. It is found that the plasma rotation has a significant increase at the transient Te transition region (r/a ~0.5). The high frequency fluctuation (~100 kHz) is significantly decreased and the low frequency fluctuation (~10 kHz) is increased. The increase of the plasma rotation and suppression of high frequency fluctuation around the Te transition region suggest that the E×B flow shear may play crucial roles during the nonlocal response. 
Monday, November 5, 2018 3:48PM  4:00PM 
CO5.00010: Different transport regimes by flow control in a magnetized offaxis heated plasma Bart G.P. Van Compernolle, Matthew J Poulos, Suying Jin, George J Morales Results of a basic heat transport experiment^{ }at LAPD involving an offaxis heat source are presented. A ringshaped electron beam source injects low energy electrons (below ionization energy) along a strong magnetic field into a preexisting, large and cold plasma, resulting in a long, hollow, cylindrical region of elevated plasma pressure. Azimuthal sheared flows and axial flows are present as a consequence of the boundary conditions at the ringsource. Previously, two regimes were identified: 1) a regime dominated by avalanches, consisting of sudden intermittent rearrangements of the pressure profile triggered by the rapid growth of driftAlfven waves. 2) A latestage state dominated by sustained driftAlfven wave activity following a global collapse of the density profile. Recently, a new ringsource configuration has been implemented that allows active control of the plasma flows. The experiment now offers control over the size and the frequency of the avalanches, including their full suppression. Another regime has been found that under certain flow conditions generates a single frequency, maserlike mode, that causes enhanced transport. 
Monday, November 5, 2018 4:00PM  4:12PM 
CO5.00011: On the Transport Physics of the Density Limit Patrick H. Diamond, Rima J. Hajjar, Mikhail A. Malkov, Zhibin B. Guo Proximity to the density limit is characterized by degraded particle confinement, rise in edge turbulence and collapse of zonal flows. We present extensive theoretical work (Hajjar et al. 2018, Phys. Plasmas 25, 062306) which shows that the key parameter governing the flow collapse transition is electron adiabaticity. We show that zonal flow production drops precipitously in the hydrodynamic electron regime, as the nondiffusive vorticity flux (i.e. residual stress) declines in proportion to adiabaticity. A simple physical argument establishes that the familiar cartoon of zonal flow production by eddy tilting fails in the hydrodynamic regime, as there causality and Reynolds stress tend to decouple. We show that reduced zonal flow production is the mechanism for particle confinement degradation in Lmode, and present a feedback loop mechanism for the cooling front. Several associated experimental studies are suggested. We also discuss the density limit in Hmode and its relation to the H to L back transition. A key element here is the invasion of the edge by turbulence, which spreads from the SOL. 
Monday, November 5, 2018 4:12PM  4:24PM 
CO5.00012: A new, fluxbalanced HasegawaWakatani model Andrew J Majda, Di Qi, Antoine Cerfon The modified HasegawaWakatani (mHW) model [1] is the simplest twofield fluid model for the study of the interplay between drift waves and zonal flows. Unlike the HasegawaMima (HM) model [2], the mHW model contains a drift wave instability, and unlike the original HW model, the mHW model describes the formation of robust zonal structures. However, a limitation of the mHW model is its treatment of the electron dynamics parallel to the magnetic field, which prevents it from converging to the modified HM (mHM) model [3] in the appropriate collisionless limit. We present a new HW model with an improved treatment of the electron parallel dynamics to address this limitation, which we call fluxbalanced HW (bHW) model. We demonstrate that the bHW model converges to the mHM model in the collisionless limit as desired, and has additional attractive properties, such as the development of uniformly stronger and more turbulent zonal jets than in the mHW model, and an enhanced variability in the turbulent fluctuations. [1] R. Numata, R. Ball, and R. L. Dewar, Phys. Plasmas, 14, 102312 (2007) [2] A. Hasegawa and K. Mima, Phys. Fluids, 21, 87 (1978) [3] W. Dorland and G. W. Hammett, Phys. Fluids B 5, 812 (1993) 
Monday, November 5, 2018 4:24PM  4:36PM 
CO5.00013: Onset of anomalousresistivityfacilitated magnetic reconnection in an evolving current sheet. Ryan L White, Nuno F Loureiro, Boris Breizman, Giannandrea Inchingolo, Lucio M Milanese Reconnection in hightemperature plasmas is associated with the large values of current density. The electronion friction in this context is traditionally modeled with the classical Spitzer resistivity, which is very small in most laboratory and astrophysical plasmas. We present a theory of the onset of magnetic reconnection in a current sheet through the development of anomalous resistivity in a kinetically unstable current profile. It is found that for sufficiently low aspect ratio current sheets (L/a not too large), kinetic instabilities are triggered prior to the system becoming plasmoid unstable. The resulting reconnection rate is determined by a marginal stability model of anomalous resistivity, balancing flux convection and diffusion. For typical parameters in an Ohmically heated tokamak, we find a reconnection rate in a sawtooth crash which is consistent with observations. 
Monday, November 5, 2018 4:36PM  4:48PM 
CO5.00014: Conservative treatment of curvilinear perfectconductor boundaries in the energyconserving implicit DarwinPIC algorithm. Luis Chacon, Guangye Chen We discuss the extension of the recently developed fully implicit, curvilinear Darwin particleincell algorithm^{1} to deal with arbitrary curvilinear perfectconductor boundaries. Unlike standard explicit PIC schemes, fully implicit PIC algorithms allow exact discrete energy and charge conservation, and feature superior stability properties.^{1,2,3,4} However, DarwinPIC formulations are notoriously brittle when dealing with realistic boundaries in multiple dimensions, as they often require artificial boundary conditions.^{5} Here, we extend the implicit DarwinPIC algorithm to deal with arbitrary curvilinear perfectconductor boundaries while retaining its exact conservation properties.^{6} We will introduce the formulation and demonstrate its accuracy and efficiency properties with various numerical experiments. 1. Chacon and Chen, JCP, 316 (2016) 2. Chen, Chacon, and Barnes, JCP 230 (2011) 3. Chen and Chacon, CPC, 185 (2014) 4. Chen and Chacon, CPC 197 (2015) 5. Hewett, CPC 84 (1994) 6. Chacon and Chen, JCP, submitted (2018)

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