Ray Tracing Analyses of Current-Free ECRH Plasmas in Heliotron E

Abstract

Ray tracing calculation of both the ordinary (O) mode and the extraordinary (X) mode using the cold plasma dispersion relation were carried out for the fundamental resonance (ω=ω_ce) and the second harmonic resonance (ω=2ω_ce) in a straight-heliotron configuration, where ω_ce denotes electron cyclotron frequency. Absorption coefficients are evaluated by the optical thickness along the ray trajectories without relativistic effects. In Heliotron E, dominant contribution to the heating by electromagnetic waves launched from the low field side is the O-mode for ω=ω_ce and the X-mode for ω=2ω_ce, when single path absorption is significant and mode mixing at wall reflection is negligible. Good heating efficiency requires adjustment of the cylotron resonance at the magnetic axis, which is consistent with the experimental data.