Sputtering properties of RAFM steels under high-flux He plasma exposure

Abstract

Sputtering properties of F82H and CLF-1 RAFM (reduced activation ferritic/martensitic) steels are investigated under exposure to high-flux He plasmas (Γi∼2–4×1022m−2s−1) in PISCES-B with a low incident ion energy of ∼80eV and sample temperature, Ts, ranging from ∼573K to 1053K. Both steels are primarily alloys of Fe, Cr, and W. While sputtered W atoms were not detected during the exposure, sputtered Fe and Cr atomic fluxes were spectroscopically quantified using S/XB values of Fe I and Cr I emission lines, which were experimentally determined in this study. Sputtering yields of F82H obtained from spectroscopy agree well with those from mass loss measurements. The He+ fluence-integrated sputtering yield of F82H and CLF-1 does not depend on Ts in the range of ∼573–873K, but starts to increase at Ts ∼900K. Sputtered Fe and Cr atomic fluxes are found to drop during the plasma exposure. The reduction of sputtering yield is explained by surface enrichment of W and development of surface morphology. The surface enrichment of W was measured with Auger electron spectroscopy, and is due to the observed preferential sputtering of Fe and Cr. Cone-like structures were observed with a scanning electron microscope, which become larger with increasing Ts, and W fuzz is formed on top of the cones at Ts≥973K.