A full-wave numerical simulation of fast wave current drive in tokamak plasma with circular cross section

Abstract

A full-wave numerical simulation is presented for the analysis of fast wave current drive (FWCD) in the KSTAR tokamak currently proposed as a superconducting advanced tokamak for the national fusion program in Korea. The wave equation describing the propagation and absorption of fast wave has been derived by the reduced-order expansions and the perturbative treatment of the parallel electric field. To investigate the characteristics of FWCD in shaped tokamak geometries, flux coordinates are adopted for describing the wave equation with the help of a general analytic solution of the Grad-Shafranov equation for arbitrary choice of plasma size, aspect ratio, elongation, and triangularity. Toroidal and poloidal mode expansions and shooting method with a variable step size integrator are employed to solve the wave equation in the flux coordinates. In the simulation, a phase-shifted antenna array is used to give net toroidal momentum to electrons via electron Landau damping and transit time magnetic pumping, and a semi-analytic model for current drive is applied. As a result of the simulation, the characteristics of FWCD for various plasma and antenna parameters are discussed, and the optimum design of a FWCD system is performed for KSTAR.