RF models for plasma-surface interactions: Sheath boundary conditions with dielectrics

Abstract

Computational models for DC and oscillatory (RF-driven) sheath potentials, arising at metal or dielectric-coated surfaces in contact with plasma, are developed from first principles using particle-in-cell modeling in the VSim FDTD code. These results are used to formulate a subgrid kinetic sheath boundary condition [1], applicable in both fluid [2] and particle VSim modeling scenarios, wherein sub-grid models for sheaths or dielectric-modified sheaths retain self-consistency in modeling salient physical properties (e.g. sheath-modified particle and heat fluxes) at material surfaces. In this manner, sheath potentials, EEDF evolution, and sputtering physics associated with sheath formation can be included in macroscopic simulations which need not resolve the spatial scales of the sheath explicitly. Ultimately, the developed models will be used to simulate plasma-facing ICRF antenna structures in existing and future magnetic fusion experiments (e.g. Alcator C-Mod, ITER), assessing the efficacy of dielectric-coated antenna surfaces in reducing sputtering-induced high-Z impurity contamination of the fusion reaction. They may also have applications for industrial plasma modeling scenarios.