Tungsten monoblocks are the current design choice for the ITER divertor. However, it is questionable whether tungsten remains a viable option when moving to a power plant. One of the alternatives is a liquid metal divertor which is a possible solution to the extreme heat and particle flux that must be sustained in a fusion divertor. Liquid metals could be a viable candidate due to their resiliency to erosion and inherent immunity to defects caused by neutrons as they can be continuously replenished.
One of the limitations set on the divertor is the maximum allowed plasma core contamination due to erosion and for liquid metals particularly, evaporation. The evaporation increases with the surface temperature which sets an upper limit to the heat flux the liquid-metal based divertor can be designed to receive. However, not all the eroded particles enter the core as some are re-deposited back onto the surface. A high redeposition ratio could greatly benefit the development of liquid metals as divertor materials as higher gross erosion rates could be more acceptable and operational temperatures could be increased.
This research focuses on measuring the sputtering yield, to improve the accuracy of the calculation of the redeposition ratio, as well as measuring the redeposition effects that are expected to be dominant in a detached divertor scenario. This research is especially relevant as what is currently seen as the main redeposition effect, prompt redeposition, will be less prevalent in detached divertor scenarios. The linear device Magnum-PSI allows for experiments with the detached conditions expected to be present at the ITER/DEMO divertor. However, due to the orientation of the magnetic field and low electron temperatures in Magnum-PSI, prompt redeposition is negligible, which allows for investigation of redeposition effects caused by momentum transfer and charge exchange. While the end goal concerns liquid metals, the redeposition effects are similar regardless of how the surface was eroded. This allows us to use physical sputtering on copper targets instead of evaporating liquid metals.
