Numerical simulation of ion cyclotron heating of hot tokamak plasmas

Abstract

The authors have written a code for the solution of the integro-differential equations describing coupling, propagation and absorption of high frequency waves in the ion cyclotron frequency range in tokamak plasmas, taking into account finite Larmor radius effects and parallel dispersion. The wave equations are discretized by a semi-spectral approach, using cubic Hermite finite elements in the radial direction and an expansion in Fourier modes in the poloidal direction. The latter permits analytic evaluation of the orbit integrals along magnetic field lines in the presence of a poloidal component of the static magnetic field. Thus, the code describes mode conversion to ion Bernstein waves, ion cyclotron damping at the fundamental and at the first harmonic, and electron transit time and Landau damping in full toroidal geometry. A few simulations of ion cyclotron heating of the ASDEX tokamak are presented. They show generally good agreement with the predictions of simpler models, namely plane layered models and ray tracing. Furthermore, the simulations can be used to identify a few interesting toroidal effects, particularly regarding the efficiency of mode conversion and the propagation of ion Bernstein waves.