NUMERICAL STUDY OF NONLINEAR COUPLING OF A LOWER-HYBRID WAVE IN KSTAR

Abstract

The nonlinear coupling to the tokamak plasma of the slow wave launched by the 5.0 GHz Lower-Hybrid (LH) system, which will be used for the non-inductive current drive in the Korea Superconducting Tokamak Advanced Research (KSTAR), has been studied by using a numerical computation. The numerical analysis is based on a nonlinear equation for an electric field, with a linear plasma density profile and a linear electron temperature profile near the grill. The radiated high-power density of the LH-wave perturbs the edge plasma density and even heats the plasma in front of the grill because of ponderomotive forces resulting from the RF pressure. This paper describes the nonlinear effect of the ponderomotive force on the coupling of the slow wave at the grill edge by considering only the axial component of the ponderomotive force along the waveguide grill and the associated perturbed plasma density given by the Boltzmann relation.