Effect of ion energy and flux during deuterium plasma exposure of displacement-damaged tungsten

A systematic investigation was carried out to study the effects of ion energy and flux during deuterium (D) exposure of self-ion damaged tungsten (W) at a sample temperature of 570 K. Experimental conditions included combinations of 5 and 38 eV/D ions and fluxes of 6×1019 and 5×1020D/m2/s. The depth distribution of deuterium at the topmost 7.4 μm was determined by 3He Nuclear Reaction Analysis (NRA), while its total inventory was evaluated using both NRA and Thermal Desorption Spectroscopy (TDS). Morphological modifications at the surface were analyzed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) together with focused ion beam cutting (FIB). The experimental results show that already a flux of 5×1020D/m2/s leads to the formation of blisters on the W surface even for 5 eV/D. With 38 eV/D ions additional defects are created that trap deuterium exceeding a depth of 7.4 μm. All blisters in this study were very shallow with widths in the micrometer range and heights of only few tens of nanometers. The study revealed that blisters with a low height-to-diameter ratio are difficult to detect using scanning electron microscopy (SEM). These features could only be clearly identified through CLSM applying the differential interference contrast (DIC) mode.