Three-Dimensional Ray Tracing in Toroidal Stellarators

We have applied a fully three-dimensional ray-tracing code to stellarators to examine the propagation of electromagnetic radiation near the electron cyclotron frequency in straight stellarators, toroidal stellarators, and tokamaks. The stellarators are simulated by using numerically computed vacuum magnetic fields and are assumed to have temperatures and densities which are constant on the flux surfaces. A comparison of the topology shows that, even for large aspect ratios, the 1/R B-dependence is the dominant effect on the location of the resonance and cutoff layers in the toroidal devices. Hence, straight stellarator geometry is not appropriate for ray-tracing purposes in this parameter regime.