COMSOL Modeling for the DIII-D Helicon Antenna Test Stand Experiment*

A program integrating COMSOL modeling of the 1 MW helicon antenna has explored design parameters such as RF coupling between modules, multipactor analysis, heat dissipation and mitigation of disruption forces. A 30-module comb-line antenna is being designed for driving off-axis non-inductive current in the DIII-D tokamak using electromagnetic waves at 476 MHz and 2.1 T of magnetic field. In order to validate design criteria, an experimental module is built using a segmented version of an antenna module. This test module is fed with 7 kW of RF power (450-525 MHz), with up to 0.1 T of background magnetic field. In addition the planned 1MW stripline power feed is explored using a high-Q RF resonator designed to replicate the electromagnetic field values of the stripline and stripline-to-module connection interface using the available 7 kW of power. COMSOL was used to simulate the RF characteristics of the segmented module and to design and optimize the RF performance of the resonator. Data on the scaled module: magnetic field, electric field, temperatures and RF resonator performance are presented.