Modeling of nonlinear electron cyclotron resonance heating and current drive in a tokamak

Abstract

Electron cyclotron resonance heating and current drive are modeled in tokamak geometry taking into account nonlinear wave-particle interaction and the inhomogeneity of the distribution function on magnetic surfaces. The model includes self-consistently coupled beam tracing and Monte Carlo computations of the electron distribution function. The method of Green’s function for the computation of the generated current is described. For the Axisymmetric Divertor Experiment Upgrade [Leuterer et al., Fusion Eng. Des. 53, 485 (2001)] parameters and high beam focusing, nonlinear wave-particle interaction effects appear to be important for perpendicular launch of the microwave beam and not important for oblique launches where they stay below the “threshold.” With defocusing the beam two to three times along the direction of the magnetic field nonlinear effects of wave-particle interaction start to be important also for oblique launches. The effect of decreased current in case of increasing the microwave beamwidth is demonstrated. The decrease of both power absorption and generated current around low-order rational magnetic surfaces is found. Its possible effect on the tearing mode stability index is discussed.