Calculation of RF sheath properties from surface wave-fields: a post-processing method

It is important to understand and quantitatively model the RF sheaths that form on material surfaces when intense ICRF waves are present. A method, outlined in [1], enables calculation of the RF sheath voltage by post-processing surface RF quantities, such as the normal plasma current into the surface, from codes which employ conducting wall, rather than sheath boundary conditions (BCs). Essentially, the method recalculates the local fields near the surface in the presence of the sheath under some assumptions. The previous implementation [1], valid for slow waves when the background magnetic field was normal to the surface has now been generalized to arbitrary electromagnetic fast and slow wave polarizations and oblique magnetic fields. Verification tests and an application to the modeling of far-field sheaths in the LAPD experiment will be presented. In addition, progress on incorporating the nonlinear sheath BC directly into the Petra-M global code will be discussed.

[1] J.R. Myra and H. Kohno, EPJ Web of Conferences 157, 03037 (2017).