Ray Tracing Analyses of Lower Hybrid Waves in Heliotron/Torsatron

Abstract

Lower hybrid (LH) wave propagation and absorption caused by ion Landau damping and electron Landau damping in the heliotron/torsatron were studied for ion heating, electron heating and current drive. The analyses are based on the ray tracing method using the electromagnetic plasma dispersion relation, including warm plasma effects. In the heliotron/torsatron, the magnetic field has large ripples along the magnetic field line produced by external helical coils. This property changes the cross-sectional shape of the LH resonance layer from a circular shape in tokamaks. The refractive indices N_⊥ and N_⁄⁄, perpendicular and parallel to the magnetic field line, respectively, also change in oscillation along the ray trajectory. LH waves are absorbed at the places where the refractive index is large or at the high-field side near the helical coils.