HHFW Heating Antenna Design and Modeling for WHAM*

A major objective of the Wisconsin HTS Axisymmetric Mirror (WHAM) experiment is to apply High Harmonic Fast Wave (HHFW) heating to sloshing ion populations created by neutral beam injection (NBI) in a collisionless mirror trap. Various antenna designs were evaluated with a full wave Finite Element Method (FEM) model based on COMSOL Multiphysics' RF module, primarily utilizing a cold plasma dielectric tensor with artificial damping. A single half turn, dual half turn and single full turn antenna of various widths and radii were compared on the basis of their antenna loading impedance and the wave field profile in the plasma. Several Faraday cage and back plane designs have also been evaluated in full 3D simulations, and the predicted parasitic losses and maximum electric fields will be reported. We will also provide updates on the latest progress to include hot plasma spatial dispersion and finite Larmor radius effects into the FEM simulation via an iterative calculation with the orbit-tracing Kinetic-J code [1] in 2D geometry. Finally, we will give an overview of the installation of a 1 MW, 3.9-26.1 MHz continuous-wave RF transmitter on site, along with the transmission lines, dummy load, matching network and control system required for HHFW experiments on WHAM.

[1] D. Green, L. Berry “Iterative addition of parallel temperature effects to finite-difference simulation of radio-frequency wave propagation in plasmas” Computer Physics Communications 185 (2014) 736–743