An efficient numerical method for gyrokinetic δ f Vlasov simulations in helical plasmas

Three-dimensional configurations of helical plasmas bring numerical difficulties to gyrokinetic simulations of plasma turbulent transport in toroidal fusion devices. Watanabe et l.have investigated the ion-temperature-gradient (ITG)-driven turbulence in helical plasmas by means of the gyrokinetic Vlasov simulation code GVK [1]. Because of a large number of grid points along a magnetic field line for resolving particle motions in helical ripples, however, the CourantFriedrichs-Lewy (CFL) condition on the parallel advection term as well as the perpendicular magnetic drift term severely restricts time steps in the linear limit. To address this problem, we propose an efficient numerical method for linear analysis of instabilities in helical plasmas by means of gyrokineticδ f Vlasov simulations, employing semi-Lagrangian and additive semiimplicit Runge-Kutta schemes. The new scheme is free from the CFL restrictions for the linear terms.