Vorpal Modeling of RF Plasma Sheaths in Fusion Devices

The development of robust radiofrequency (RF) actuators for plasma heating and current drive will be critical in sustaining steady-state operation of future magnetic fusion devices. As part of this development, we explore via numerical simulation how applied RF power interacts with plasma sheaths which form near antenna hardware and other plasma-facing material surfaces. These interactions are modeled using Vorpal, a high-performance PIC/finite-difference time-domain code. Efforts include (a) PIC modeling of sheath rectification in time-varying RF sheaths near antenna surfaces, and the benchmarking of these results with other RF-SciDAC codes; (b) comparison of experimentally measured RF sheath electric fields with Vorpal models; and (c) implementation of a capacitive/resistive sheath model [Kohno & Myra, CPC 220, 129 (2017)] as a sub-grid boundary condition for macroscopic-scale time-domain modeling of RF wave propagation in a tokamak. Ongoing progress in these areas will be presented. Eventual couplings of Vorpal with materials, turbulence, and transport codes are anticipated as part of ongoing RF-SciDAC work; future efforts in these areas will also be discussed.