Investigation of ion incident angle and sheath profile in linear plasma devices

High momentum flux in the divertor plasma of a fusion reactor causes surface erosion by sputtering, which reduces the lifetime of the plasma-facing component (PFC) and degrades plasma performance. The motion of boundary plasma particles in the collisionless sheath is guided by E and B fields before striking the divertor surface. Important parameters that govern the plasma-materials interactions (PMI) are incident angle, particle energy, and surface structure. The present study focuses on linear plasma devices (DIONISOS, PISCES-A, and Magnum-PSI) assuming 45°-88° B field angle at the target surface measured from the surface normal (0°). A collisionless kinetic model was used to calculate the incident polar and azimuthal ion angle distributions (IADs) of hydrogen, deuterium, and helium under sheath potential profile assumptions considering the classical Debye sheath and/or magnetic presheath. Microtrench samples for experimental IAD verification are designed using a Monte Carlo micro-patterning and roughness (MPR) code simulating erosion patterns of tracer materials on microtrench surfaces due to physical sputtering for expected IADs. The experimental verification of IADs validates the assumptions of the sheath modeling used in the IAD calculations.