Full Wave Modeling of ICRF Heating in the Bounded, Hot, Non-Maxwellian WHAM Plasma

A 1 MW, 3-26 MHz ICRF heating system is being commissioned for the Wisconsin HTS Axisymmetric Mirror (WHAM) for resonant heating of ions at the 2nd and 3rd harmonic. The high heating power density of 25 kW/L, small plasma diameter, non-Maxwellian ion distribution due to NBI and the loss cone present a difficult modeling challenge. We start by deriving the propagation and cut-off characteristics of the fast wave within a bounded plasma column, which is complemented with 2D axisymmetric finite-element method (FEM) full-wave simulations in COMSOL Multiphysics utilizing the full anisotropic cold plasma dielectric tensor. The launch antenna design for the ICRF system was optimized in both 2D and 3D simulations.

Three different methods were used to include kinetic effects in the full wave simulations. First, the Bi-Maxwellian hot plasma tensor is used with wave vectors obtained from cold plasma bounded dispersion relations. This model demonstrates strong damping of the fast wave in the presence of sloshing fast ion populations. Second, the fully non-local, integral-differential wave equation including the contribution of the hot plasma dielectric kernel is solved, but computational challenges limit the fidelity of such a model. Finally, a time-domain, fully kinetic Particle-in-Cell simulation was performed with WarpX, and the results are compared against the frequency-domain solutions.