Temperature dependence of sputtering yields of steels with various W content for plasma facing applications

Materials are a key issue in any nuclear fusion reactor. For plasma-facing materials irradiation and sputtering limit their lifetime in a fusion power reactor. Steels allow for lower costs, reduced activation, and proven long irradiation lifetimes compared to tungsten at the expense of a lower sputtering lifetime. Several studies investigated the connected effects showing W-fuzz like surface morphology and a W enrichment through preferential sputtering, opening up a potentially significant increase of this sputtering lifetime of steels. The role of the W content in the steel is an open question. The presented exposure of 3 steels with W content from 0.5 to 2 at. % in deuterium plasma at 693–843 K sample temperature aims at resolving this. The experiments combine in-situ infrared imaging and passive spectroscopy with ex-situ ion-beam analysis. At the given conditions, a flux density independent exponential W enrichment within 70 s time-constant followed by a 1400 s time-constant nano-structure formation is observed. The overall effect is a reduction of the Fe sputtering yield by a factor 4.4, 3.0, and 2.5 for 2 %, 1.1 %, 0.5 % W steels, respectively. This factor reduces slightly with temperature by up to 20 % towards higher temperatures.