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approvedabstract_bao_sherwood2018-1.pdf2018-03-01 16:14:32Jian Bao


Author: Jian Bao
Requested Type: Pre-Selected Invited
Submitted: 2018-03-01 15:54:56


Contact Info:
University of California, Irvine
UC Irvine
Irvine, CA   92697
United States

Abstract Text:
A conservative scheme of drift kinetic electrons for gyrokinetic simulations of kinetic magnetohydrodynamic (MHD) processes in toroidal plasmas has been formulated and verified [1]. Both vector potential and electron perturbed distribution function are decomposed into adiabatic part with accurately analytic solution and non-adiabatic part solved dynamically. Since particles are only used to calculate the non-adiabatic electron response for solving the non-adiabatic vector potential through Ohm’s law, the conservative scheme minimizes the electron particle noise and avoids the cancellation problem.

The consistency between electrostatic potential and vector potential is enforced by using the electron continuity equation in this conservative scheme. This is in contrast to the conventional perturbative simulation of the long wavelength shear Alfvén waves, where both simulation and theory [2] show that an unphysically large parallel electric field is produced if this consistency is not enforced, leading to the well-known numerical difficulties.

The new scheme enables kinetic simulations of nonlinear interactions of kinetic-MHD processes spanning large ranges of temporal-spatial scales in high-β plasmas with realistic electron-to-ion mass ratio. The collisionless tearing mode, kinetic ballooning mode, and toroidal Alfvén eigenmode have been verified in GTC simulations. The grid size can be larger than the electron collisionless skin depth (d_e) for long wavelength modes with k_⊥^2 d_e^2≪1. The dampings of toroidal Alfvén eigenmode in JET and reversed shear Alfvén eigenmode in DIII-D by kinetic electron effects have been measured in GTC simulations using conservative scheme. The nonlinear saturation of Alfvén eigenmodes by self-generated zonal flow and zonal current will be presented. (In collaborations with GTC team and supported by DOE SciDAC ISEP.) [1] J. Bao, D. Liu, Z. Lin, POP 24, 102516(2017); [2] J. Bao, Z. Lin, and Z. X. Lu, POP 25, 022515(2018).