Tungsten erosion under combined hydrogen/helium high heat flux loading

Abstract

We investigated the erosion behaviour of tungsten under irradiation with a fusion reactorrelevant H/He mixture of 94%/6% at a power density of 10 MW/m². The investigated surface temperatures range up to 2000°C and the range of the applied fluence was up to 7×10 25 m -2 . The erosion yield we observe exceeds the value expected from physical sputtering data by a factor of 2. In addition we observe an Arrhenius-like increase of the erosion yield with temperature with an activation energy of 0.04 eV.

Surface morphology changes of tungsten exposed to high heat loading with mixed hydrogen/helium beams

“…In comparison with 6 at.% He loading [10] our new results show a lower bubble density in the near-surface layer for the same He fluence at the same surface temperature. Fig.…”

“…An equilibrium is reached between surface erosion and bubble formation and the thickness of the affected layer is nearly constant above a fluence of 1 Â 10 25 m À2 . We note that the thickness of the affected layer, compared with the 6 at.% He loading, decreases from 400 ± 100 nm to about 250 nm in case of the 1 at.% He loading [9,10] at constant total fluence. Further, we observed the same surface-and bubble layer structures independent of the surface temperature in the investigated temperature range between 1000°C and 2000°C.…”

“…The applied loading conditions were similar to the previously performed experiments where a particle composition of 94 at.% H and 6 at.% He was used [9,10]. The experiments were performed at 10 ± 0.5 MW/m 2 central heat flux and pulses of 30s duration to ensure the comparability of the results.…”

Synergistic effects of ELMs and steady state H and H/He irradiation on tungsten

“…the surface is black. There is no reason to assume that the cleavages, for the 600 • C H/He-exposure, and the cavities, for 1000 • C and 1500 • C H/He-exposure, as reported in literature [14] would be different for these specimens.…”

“…Probably some of the material modifications by helium, i.e. the surface extrusions and/or the sub-surface cavities [14], are responsible. While also the 1500 • C H/He sample has these cavities and extrusions, the recrystallization has weakened the material.…”