Analytical, numerical, and experimental investigation of nonlinear radio-frequency sheaths

Recent progress made toward the development, implementation, and benchmarking of a self-consistent radio-frequency (RF) sheath model [1] is presented. RF sheaths form on plasma facing components during the injection of RF power in the ion-cyclotron range of frequencies (ICRF). Plasma ions are accelerated across the sheath potential where they impact the material surface causing several deleterious effects such as erosion of the wall material and the sputtering of impurities which contaminate the plasma. Sheath rectification in the WEST tokamak due to ICRF is modeled using the three-dimensional finite element code Petra-M, which includes realistic antenna, limiter, and wall geometry [2]. In simplified geometries, analytical results are leveraged to demonstrate that self-consistent RF sheath—plasma interactions host a rich set of nonlinear features such as multivaluedness, instability, hysteresis and spontaneous symmetry breaking [3]. Finally, a basic RF sheath-plasma experiment is performed on the Large Plasma Device (LAPD) which qualitatively demonstrates the existence of a nonlinear hysteresis associated with sheath-plasma interactions.