Global Gyrokinetic Simulations of Kinetic Ballooning Mode in NSTX-U Plasmas

Linear, local gyrokinetic simulations predict that the Kinetic Ballooning Mode (KBM) instability occurs at the plasma profile threshold and could contribute to the turbulence-driven ion thermal transport in the core and pedestal of NSTX-U plasma [1]. This work reports the first-ever global gyrokinetic simulations of KBM in projected discharges of NSTX-U using realistic magnetic geometry and plasma profiles. The Gyrokinetic Toroidal Code (GTC) [2] is employed to carry out linear and nonlinear simulations without ExB flow shear. Simulations are performed using both adiabatic and kinetic electrons. Linear simulations show that the KBM is present in both the core and pedestal regions of NSTX-U. The kinetic electrons reduce the linear growth rate of the KBM instability compared to that of the adiabatic electrons. Nonlinear simulations illustrate that the KBM saturates via nonlinear mode coupling, where the self-generated zonal flow is also found to play an essential role in regulating turbulence and transport.

[1] C. F. Clauser et al. Phys. Plasmas 29, 102303 (2022).

[2] Z. Lin et al. Science 281, 5384 (1998).