Rodrigo Mateus

This paper gives an overview of erosion and migration studies of tungsten (W) in the WEST tokamak during its Phase 1 (2016-2021) and Phase 2 (from 2022) experimental campaigns with a focus on plasma-facing components (PFCs) at the divertor. In Phase 1, gross erosion of PFCs is in line with observations from other major fusion devices and attributed to low-Z impurities in the plasma. In addition, a strong asymmetry is observed between the high- (inner) and low-field (outer) side divertor targets, in favour of the inner side. Net erosion at rates of <0.5 nm/s is measured around the strike points while the remaining areas are dominated by net deposition. The thickest deposited layers (up to 50 m) with the most complex structures result from a cumulated plasma exposure of ~7 h. The overall erosion-deposition pattern is further influenced by the strong magnetic ripple of WEST, which can result in almost an order of magnitude difference between the maxima and minima of the ripple. In Phase 2, increasing plasma fluence leads to the deposits growing to hundreds of micrometres in thickness. At the same time, erosion proceeds at a constant rate and can reach values up to 30 m in ~18 h of plasma time. In the main chamber, erosion is weaker than at the divertor but especially at low densities it can result in notable transport of W into the core. In addition, upon switching on the ICRF antennas, W sputtering on the close-by limiter structures can increase by a factor of more than 10. Modelling is able to catch many of the observed phenomena in Phase 1, with the exception of the inner-outer asymmetry and the formation of the thick deposits. In contrast, the patterns during the high-fluence operations in Phase 2 require more work to be reproduced.

In fusion materials research using ion beam analysis techniques, the reactions ⁹Be(³He,p _i )¹¹B (i = 0, 1, 2…) are relevant to probe Be-related plasma-wall interactions. The cross sections for this reaction have been examined previously; nevertheless, there is a ∼40% difference in the studied energy interval between the two most relevant earlier studies. Therefore, a new data set for the differential cross sections ⁹Be(³He,p _i )¹¹B for the proton groups i = 0, 1, …, 9 is given. The measurements were performed using a thin beryllium film in the laboratory energy range from 1.0 MeV to 2.5 MeV in steps of 50 keV for lab angles from 115° to 165° to the incoming beam direction in steps of 10°. Additional measurements for intermediate angles were performed over the same energy range in steps of 250 keV. The results are in good agreement with one of the previous studies and a benchmarking measurement was performed against the yield of a beryllium thick target at 2.5 MeV for 135°.