Multi-channel analyzer investigations of ion flux at the target surface in pilot-PSI

Pilot-PSI is a linear plasma device designed for investigations of plasma-surface interaction. A cascaded-arc plasma source operated in argon or/and hydrogen generates a high-density plasma that is magnetically confined on the vessel's axis, resulting a plasma column of about 1-2 cm in diameter which interacts with a solid target. A multi-channel analyzer was constructed to study the radial distribution of the ion flux at the target surface. The analyzer was placed in the centre of Pilot-PSI target and current-voltage characteristics were drawn for five collectors disposed at different radial positions. The ion flux was estimated from the ion part of the current-voltage characteristic for each collector. For densities lower than 1019 m^-3 (significantly below the maximum performance of Pilot-PSI), fluxes of up to 10²³ ions/m²s were measured. A difference of a factor four was measured between the maximum ion flux in the centre of the target and the flux at the edge, at a radial position of 1 cm.