Impact of simultaneous W deposition and He plasma exposure on mechanical properties of tungsten

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Tungsten is a candidate material for plasma facing components in future fusion reactors such as STEP and DEMO and is the chosen material for the diverter in ITER. The influence of He plasma interactions with tungsten is a fertile area of study with extensive work having been carried out a variety of fusion relevant temperature, fluences and ion energies. The influence of He has been shown to vary at different temperatures with smaller nanobubbles formed at less than 873 K, larger ones above this temperature and a nanostructure knows as fuzz at temperatures between 900-2000 K, with larger voids formed at temperatures above 2000 K. He interactions with tungsten has also been shown to have an influence on the recrystallization properties of tungsten which is related to the temperature of irradiation and consequently the size of bubble formation. This is of interest as recrystallization influences the mechanical performance of tungsten and may increase the likelihood of micro-cracking during operations at high temperatures. Recent work has shown that the presence of tungsten particles during He plasma irradiation has resulted in the enhanced formation of fuzz. This could be of interest for future fusion reactors where there will be some sputtered tungsten present in the plasma. It is of interest to see what the simultaneous impact of deposition of tungsten from an external source with He irradiation at lower temperatures than those required for fuzz formation will be in the nanobubble formation regime and additionally whether this influences the retardation of recrystallization that has been observed following He exposure of tungsten previously. In order to investigate this process, He plasma exposures with simultaneous tungsten deposition will be carried out in collaboration with Prof. Cormac Corr at ANU on tungsten material relevant to the UK Atomic Atomic Energy Authority 'STEP' (Spherical Tokamak for Energy Production) programme. Annealing studies will be carried out on these samples. Following this time will be applied for to use diffraction techniques using the national lab facilities at Harwell in order to measure He bubble size in the exposed samples, which will be correlated to recrystallization via microscopy techniques at Manchester. This is of vital performance in order to understand the engineering performance of future tungsten components and their suitability.The objectives of the project will be to:Carry out simultaneous He irradiation and tungsten deposition on STEP relevant tungsten material at a range of temperatures and fluencesCharacterise the He bubble sizes using imaging and small-angle scattering techniquesCorrelate the bubble formation with impact on recrystallization/other mechanical properties