Replication of near-supersonic, runaway electron induced dust-wall impacts using a two-stage light-gas gun

Tokamak disruptions can generate relativistic runaway electrons (REs) that preserve a significant fraction of the original plasma current. Upon termination on plasma-facing components (PFCs), REs are known to lead to bulk melting [1] and have been recently observed to lead to material explosions as well as to the expulsion of fast solid debris [2]. The solid dust particles are ejected with speeds of the order of km/s and their unavoidable mechanical collisions with the vessel yield further delocalized damage [2,3]. The physics of dust-PFC impact damage have been studied through experiments that launch dust to near supersonic speeds using First Light Fusion's two-stage light-gas gun (12.7 mm diameter bore, 7.5 m long [4]). Spherical molybdenum particles with a diameter of 71 um have been launched inside a 2-part sabot to velocities of ~1-2km/s towards cryogenically cooled TZM targets. The set up mimics recent observations at the FTU tokamak [2]. The crater geometry has been analyzed with surface techniques. The effect of the PFC temperature (room vs cryogenic) on the crater dimensions and crater micro-morphology is discussed. [1] G. F. Matthews et al., Phys. Scr. T167, 014070 (2016) [2] M. De Angeli et al., Nucl. Fusion 63, 014001 (2023) [3] P. Tolias et al., arXiv:2208.02897 (2023) [4] T. J. Ringrose et al., Procedia engineering 204, 344-351 (2017)