Coupling Analysis for the ICRF Resonant Cavity Launcher on DIII-D

The coupling properties of the ion-cyclotron range of frequencies (ICRF) resonant cavity launcher for DIII-D were investigated with a two-dimensional (2-D) model. In the context of the magnetostatic approximation, Poisson's equation was solved for the vector potential with a self-consistent antenna current distribution. The tool of analysis is a fast 2-D Poisson solver which takes into account the plasma medium and the shape of the cavity wall and antenna cross section. This permits the design of the optimum configuration for such a launcher to be used on the DIII-D tokamak. Extensive parametric studies of the launcher loading impedance were carried out. It was found that the antenna-plasma distance and the edge density gradient are the two most critical parameters determining the coupling. Criteria were also established to optimize the power-handling properties of the cavity coupler.