Comparison of C-Mod and WEST ICRF Experiments with 3D Full Wave Simulations

Reliable modeling of ICRF antenna performance is essential for interpreting current experiments and designing future ICRF systems. Simulation tools such as Petra-M and COMSOL can now incorporate realistic 3D antenna geometries, plasma profiles, and the sheath boundary condition [Myra 2021 JPP 87 905870504], enabling predictions of ICRF-enhanced potentials and impurity sputtering. This work presents efforts to validate these tools against ICRF experiments on the C-Mod and WEST tokamaks. First, the C-Mod four-strap field-aligned antenna was implemented in Petra-M. The simulated sheath potential on the antenna limiters reproduces the experimental trends observed during power tapering experiments. In scenarios with low single-pass absorption, simulations also predict enhanced sheath potentials on a distant poloidal limiter in the far field of the antenna, consistent with observations. The simulated antenna loading during ELMs follows experimental trends and is driven more by the pedestal density gradient than by proximity to the cutoff. Petra-M further predicts unintended excitation of high k_|| modes during monopole phasing operation, consistent with experimental observations of poor mode conversion efficiency. On WEST, a large database of plasma potential profiles around an active ICRF antenna was assembled using reciprocating emissive probes. Comparisons between these measurements and simulations will be presented.

Supported by US DoE Awards DE-SC0014264 and DE-AC02-09CH1146.