A validation study of a bounce-averaged kinetic electron model in a KSTAR L-mode plasma

Abstract

We extend the bounce-averaged kinetic (BK) electron model to be applicable in general tokamak magnetic geometries and implement it on the global δf particle-in-cell gyrokinetic code gKPSP. We perform a benchmark study of the updated BK model against the gyrokinetic electron model in flux-tube codes, CGYRO and GENE. From the comparisons among the simulations based on the local parameters of a KSTAR L-mode plasma, we confirm a reasonable agreement among the linear results from the different codes. In the nonlinear gKPSP simulation with a narrow plasma gradient region whose width comparable to the mode correlation length, ion and electron heat fluxes are compatible with those calculated by CGYRO. However, with an unstable region sufficiently wider than the mode correlation length, gKPSP predicts 2-3 times larger turbulent heat fluxes. Taking into account the differences between the flux-tube and global simulations, the overall agreement is encouraging for further validation and development of the BK electron model. In global simulations using a wide range of the experimental plasma profiles, we find an intricate coupling of turbulence spreading and a zonal flow in determining the radial profiles of turbulent heat fluxes, which has not been reported to date.