A high-power helicon antenna for the DIII-D tokamak and its electromagnetic aspects

A comb-line antenna to demonstrate efficient off-axis non-inductive current drive from the absorption of toroidally directed very high harmonic fast waves is being designed and built for DIII-D. The antenna consists of a toroidal array of 30 modules, spanning 1.7 m on the outer vessel wall just above the tokamak midplane. This antenna will be fed with 1 MW of RF power at 476 MHz through a stripline (SL) feed on both sides inside the vacuum vessel. COMSOL Multiphysics, a commercial finite element analysis software, was used to perform the RF analysis and the induced force analysis due to plasma disruption events on the whole antenna system. Results on the RF performance of the SL and the RF coupling into and between the modules, and the SL and modules' RF losses will be presented. In addition, the disruption induced current and forces are shown, and a method to mitigate them is presented.