Ray-tracing analysis of electron-cyclotron-resonance heating in straight stellarators

A ray tracing computer code is developed and implemented to simulate electron cyclotron resonance heating (FCRH) in stellarators. A straight stellarator model is developed to simulate the confinement geometry. Following a review of FCRH, a cold plasma model is used to define the dispersion relation. To calculate the wave power deposition, a finite temperature damping approximation is used. 3-D ray equations in cylindrical coordinates are derived and put into suitable forms or computation. The three computer codes, MAC, HEFA, and GROUT, developed for this research, are described next. FCRH simulation is then carried out for three models including Heliotron E and Wendelstein VII A. Investigated aspects include launching position and mode scan, frequency detuning, helical effects, start-up, and toroidal effects. Results indicate: (1) an elliptical waveguide radiation pattern, with its long axis oriented half-way between the toroidal axis and the saddle point line, is more efficient than a circular one; and (2) mid-plane, high field side launch is favored for both O- and X-waves.