Ray Tracing near the Electron Cyclotron Frequency with Application to EBT

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Abstract
The general problem of ray tracing in the electron cyclotron range of frequencies is addressed with the view of applying geometrical optics techniques to microwave heating in ELMO Bumpy Torus (EBT). It is shown that the usual formulation of geometrical optics breaks down at cyclotron resonance due to the large anti-Hermitian part of the dispersion tensor. A consistent eikonal expansion is presented which is valid near cyclotron resonance for cases in which the waves are weakly damped. The geometrical optics code, RAYS, which was developed for the EBT study is described. Ray tracing in plane-stratified plasma geometries is discussed and examples given of the various types of ray paths which occur in plasmas stratified perpendicular to the magnetic field and stratified along magnetic field lines. The application of ray tracing techniques to EBT is discussed and typical results are presented of rays traced in a bumpy cyclinder magnetic-field configuration with plasma parameters characteristic of EBT-I.