The effects of high fluence mixed-species (deuterium, helium, beryllium) plasma interactions with tungsten

Abstract W targets are exposed to D2−Be, He, D2−He and D2−Be−He plasmas in the linear-plasma-device PISCES-B to simulate the conditions expected at W strike-points in an ITER all W metal divertor scenario. In D2−Be and He plasmas, target temperatures in the range 1070–1320 K lead to surface layers of Be–W alloy or nano-structured W morphology, respectively, but below 900 K, neither types of layer are found to form. Both processes have kinetics reminiscent of diffusion. Alloying kinetics are optimal when surface Be availability is maximized through the formation of a deposited Be over-layer. Nano-structured layer growth at 1120 K is most rapid for incident He ion fluxes above 7 × 1021 m−2s−1. In D2−0.1He plasmas, a mixture relevant to divertor exhaust, small Be or C fractions can significantly reduce nano-structure growth in favor of the formation of a mixed material Be−W alloy or C layer.