Liquid metals as a divertor plasma facing material explored using the Pilot-PSI and Magnum-PSI linear devices

Abstract For DEMO and beyond liquid metal plasma facing components are considered due to their resilience to erosion through flowed replacement, potential for cooling beyond conduction and inherent immunity to many of the issues of neutron loading compared to solid materials. The development curve of liquid metals is behind that of e.g. tungsten however and tokamak-based research is currently somewhat limited in scope. Therefore investigation in linear plasma devices can provide faster progress under controlled and well-diagnosed conditions in assessing many of the issues surrounding the use of liquid metals. The linear plasma devices Magnum-PSI and Pilot-PSI are capable of producing DEMO relevant plasma fluxes which well replicate expected divertor conditions, and the exploration of physics issues for tin (Sn) and lithium (Li) such as vapour-shielding, erosion under high particle flux loading and overall power handing are reviewed here. A deeper understanding of erosion and deposition through this work indicates that stannane formation may play an important role in enhancing Sn erosion, while on the other hand the strong hydrogen isotope affinity reduces the evaporation rate and sputtering yields for Li. In combination with the strong re-deposition rates which have been observed under this type of high density plasma this implies an increase in the operational temperature range, implying a power handling range of 20-25 MW m -2 for Sn and up to 12.5 MW m -2 for Li could be achieved. Vapour shielding may be expected to act as a self-protection mechanism in reducing the heat load to the substrate for off-normal events in the case of Sn, but may potentially be a continual mode of operation for Li.