Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session VI2: MFE: Turbulence & Transport IIInvited

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Sponsoring Units: DPP Chair: Walter Guttenfelder, Princeton Plasma Physics Laboratory Room: 210 CDGH 
Thursday, November 3, 2016 3:00PM  3:30PM 
VI2.00001: New Frontiers In TrappedElectronMode Turbulence Invited Speaker: M.J. Pueschel In tokamak core plasmas, trapped electron modes (TEMs) and their associated turbulence have long been identified as a central driving mechanism of heat and particle flux in electronheated scenarios. Plasma parameters and magnetic geometries very different from such standard cases, however, can showcase new and important aspects of TEM turbulence; here, three examples are discussed. First, the outer radii of improvedconfinement Madison Symmetric Torus reversedfield pinch discharges exhibit strong pressure gradients, which can overcome magnetic shear stabilization to drive TEM turbulence with exceptionally strong zonal flows. The resulting large Dimits shift collapses upon the inclusion of residual tearing fluctuations that short out the zonal flows to a significant degree. Second, on the low end of the magnetic shear spectrum, TEMs are seen in simulations of Helically Symmetric eXperiment stellarator plasmas. As before, zonal flows result from density gradient drive and affect turbulent saturation, despite indications that zonal flow shearing is insufficient, indicating catalyzed energy transfer to stable modes as the dominant process. The latter is furthermore supported by the nonlinear coalescence of a coherent structure comprised of stable eigenmode amplitudes. Third, the steep gradients in tokamak pedestal scenarios are able to bring about new excitation states whereby TEMs can take on tearingparity structures, while remaining clearly distinct from microtearing modes. Such TEMs require a nonzero bounce average perturbation, which can be the result of spatial or temporal decorrelation as well as asymmetric magnetic geometries, all of which are more common in largegradient regions in the plasma edge. An improved understanding of such highly excited TEMs may help understand pedestal microturbulence and predict Hmode performance in future reactors. [Preview Abstract] 
Thursday, November 3, 2016 3:30PM  4:00PM 
VI2.00002: Verification of Gyrokinetic codes: theoretical background and applications. Invited Speaker: Natalia Tronko In fusion plasmas the strong magnetic field allows the fast gyro motion to be systematically removed from the description of the dynamics, resulting in a considerable model simplification and gain of computational time. Nowadays, the gyrokinetic (GK) codes play a major role in the understanding of the development and the saturation of turbulence and in the prediction of the consequent transport. We present a new and generic theoretical framework and specific numerical applications to test the validity and the domain of applicability of existing GK codes. For a sound verification process, the underlying theoretical GK model and the numerical scheme must be considered at the same time, which makes this approach pioneering. At the analytical level, the main novelty consists in using advanced mathematical tools such as variational formulation of dynamics for systematization of basic GK code's equations to access the limits of their applicability. The indirect verification of numerical scheme is proposed via the Benchmark process. In this work, specific examples of code verification are presented for two GK codes: the multispecies electromagnetic ORB5 (PIC), and the radially global version of GENE (Eulerian). The proposed methodology can be applied to any existing GK code. We establish a hierarchy of reduced GK VlasovMaxwell equations using the generic variational formulation. Then, we derive and include the models implemented in ORB5 [1] and GENE inside this hierarchy. At the computational level, detailed verification of global electromagnetic test cases based on the CYCLONE are considered, including a parametric $\beta$scan covering the transition between the ITG to KBM and the spectral properties at the nominal $\beta$ value [2]. Bibliogpraphy: [1] N.Tronko, A.Bottino and E.Sonnendruecker, Second order gyrokinetic theory for ParticleInCell codes, to appear in Phys.Plasma. [2] T.Goerler, N.Tronko, A.Bottino et al, Intercode comparison of gyrokinetic global electromagnetic codes, to appear in Phys.Plasma. [Preview Abstract] 
Thursday, November 3, 2016 4:00PM  4:30PM 
VI2.00003: Impact of electromagnetic stabilization, small scale turbulence and multiscale interactions on heat transport in JET Invited Speaker: Paola Mantica Heat transport experiments in JET, based on ICRH heat flux scans and temperature modulation, have confirmed the importance of two transport mechanisms that are often neglected in modeling experimental results, but are crucial to reach agreement between theory and experiment and may be significant in ITER. The first mechanism is the stabilizing effect of the total pressure gradient (including fast ions) on ITG driven ion heat transport. Such stabilization is found in nonlinear gyrokinetic electromagnetic simulations using GENE and GYRO, and is the explanation for the observed loss of ion stiffness in the core of high NBIpower JET plasmas. The effect was recently observed also in JET plasmas with dominant ICRH heating and small rotation, due to ICRH fast ions, which is promising for ITER. Such mechanism dominates over ExB flow shear in the core and needs to be included in quasilinear models to increase their ability to capture the relevant physics. The second mechanism is the capability of small scale ETG instabilities to carry a significant fraction of electron heat. A decrease in T$_{\mathrm{e}}$ peaking is observed when decreasing Z$_{\mathrm{eff\thinspace }}$T$_{\mathrm{e}}$/T$_{\mathrm{i}}$, which cannot be ascribed to TEMs but is in line with ETGs. Nonlinear GENE singlescale simulations of ETGs and ITG/TEMs show that the ITG/TEM electron heat flux is not enough to match experiment. TEM stiffness is also much lower than measured. In the ETG single scale simulations the external flow shear is used to saturate the ETG streamers. Multiscale simulations are ongoing, in which the ion zonal flows are the main saturating mechanism for ETGs. These costly simulations should provide the final answer on the importance of ETGdriven electron heat flux in JET. [Preview Abstract] 
Thursday, November 3, 2016 4:30PM  5:00PM 
VI2.00004: MultiChannel Validation of Nonlinear Gyrokinetic Simulations in Alcator CMod Imode Plasmas Invited Speaker: A. J. Creely New multichannel validation of nonlinear gyrokinetic simulations (GYRO) is carried out for Imode plasmas on Alcator CMod, utilizing heat fluxes, profile stiffness, and density and temperature fluctuations. Imode plasmas are characterized by high energy confinement, similar to Hmode, but with Lmodelike particle confinement, making them favorable for reactors due to natural absence of ELMs, but without impurity accumulation [Whyte NF 2010]. At CMod, Imode plasmas have been obtained across a wide range of plasma currents (Ip $=$ 0.551.2MA) and magnetic fields (Bt $=$ 2.88.0T). Imode is also actively studied at ASDEX Upgrade, DIIID and other tokamaks [Hubbard NF 2016]. Open questions remain regarding core transport in Imode compared to L and Hmode, making validation studies in Imode of great interest. Previous work at CMod found that ITG/TEMscale GYRO simulations can match both electron and ion heat fluxes within error bars in Imode [White PoP 2015], suggesting that multiscale, crossscale coupling effects [Howard PoP 2016] may be less important in Imode than in Lmode. Adding the constraint of experimental perturbative heat diffusivity, however, revealed that ITG/TEM scale simulations do not adequately capture the high profile stiffness in Imode [Creely NF 2016]. These results motivated more comprehensive comparisons of gyrokinetic simulations with Imode plasmas. This talk expands upon past Imode GYRO validation work to simultaneously constrain nonlinear gyrokinetic simulations with experimental electron and ion heat fluxes, electron temperature fluctuations measured with Correlation ECE, density fluctuations measured with Phase Contrast Imaging and reflectometry, and the temperature profile stiffness measured using partial sawtooth heat pulses. [Preview Abstract] 
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