Modelling of the effect of particle species on beam losses in W7-X

In Wendelstein 7-X (W7-X), future campaigns will include H, D and He as both NBI injection and target plasmas but, so far, only H injection and target plasmas have been extensively performed. The species effect on the beam-ion confinement and associated power loads has been studied with the ASCOT code to estimate the location and intensity of the hot spots. For this analysis, standard, high and low mirror configurations were considered to provide results covering the variation of the mirror term most likely to affect the beam-ion behaviour. Beam-ion losses were highest for D beams and lowest for He beams. Changing the target plasma from hydrogenic species to helium also produced higher losses. Hot-spot analysis showed peak loads up to 3 MW m−2 for D beams, with 1 MW m−2 and 0.1 MW m−2 for H and He beams,
respectively. Losses were predominantly to carbon components independent of the mirror term.
This is particularly apparent for the low-mirror configuration, showing that 97%–99% of the power loads avoid the more delicate steel components. The results of the helium injection and target plasmas can be validated against experimental results in the upcoming campaign to support the results for the deuterium modelling.