EUROFER as wall material: Reduced sputtering yields due to W surface enrichment

The performance of EUROFER steel under high flux low energy plasma bombardment is being analyzed. EUROFER contains, other than Fe and Cr, important concentrations of heavy elements with W being the most prominent component with 0.4at.%. These different components in EUROFER will be eroded differently, leading to changes in surface composition and erosion yield. The plasma exposure was performed in the plasma generator PISCES-A with the parameter ranges of ion energies between 90 and 190eV, exposure temperatures between 80 and 500°C and fluences between 3×1023 and 6×1025m−2. The erosion yield was mainly determined by weight-loss measurement, and the surface composition after the exposure was analyzed by various ion beam analysis methods. For temperatures below 180°C the erosion yield of EUROFER was lower than for pure Fe already at the lowest fluence of 3×1023D+m−2, and decreased further to values of less than 1/10 of those for Fe at 6×1025D+m−2. Ion beam analysis showed the enrichment of W at the exposed surface correlating with the yield reduction; however, the experimental depth resolution of about 1nm did not allow resolving the predicted W enrichment within the first two monolayers. Therefore, it remains unclear whether the W enrichment is the only reason for the yield reduction or if surface oxidation and topography changes contribute to the observed effects. First results for different surface temperatures, however, indicated that at 500°C the erosion yield remains close to the values for pure Fe, indicating that the exposure temperature is also an important factor for the sputtering process of EUROFER.