A new hybrid simulation model for tokamak plasma turbulence

Abstract

A novel kinetic-fluid hybrid model is developed for electromagnetic plasma turbulence in tokamak geometry. In this model, by combining kinetic and fluid approaches, ions are treated with the conventional gyrokinetic particle-in-cell method, while the bounce averaged drift-kinetic method is used for trapped electrons, and passing electrons are modeled as a massless fluid to avoid numerical instabilities due to fast parallel motions of electrons. The new model is implemented in a global gyrokinetic code gKPSP (Kwon et al., 2012). In benchmark tests for linear electromagnetic instabilities, this model shows good agreement with the global gyrokinetic codes GENE and GTC. By combining kinetic and fluid approaches, it is demonstrated that electromagnetic simulations can be reliably performed with only a modest increase of numerical costs. The new model is employed to study the effects of plasma elongation on kinetic ballooning mode (KBM). It is found that the elongation has a stabilizing effect on KBM, which is consistent with the broadened parallel wave number spectrum of KBM instabilities.