Surface cracking and melting of different tungsten grades under transient heat and particle loads in a magnetized coaxial plasma gun

Surface damage of pure tungsten (W), W alloys with 2 wt.% tantalum (W–Ta) and vacuum plasma spray (VPS) W coating on a reduced activation material of ferritic steel (F82H) due to repetitive ELM-like pulsed (∼0.3 ms) deuterium plasma irradiation has been investigated by using a magnetized coaxial plasma gun. Surface cracks appeared on a pure W sample exposed to 10 plasma pulses of ∼0.3 MJ m−2, while a W–Ta sample did not show surface cracks with similar pulsed plasma irradiation. The energy density threshold for surface cracking was significantly increased by the existence of the alloying element of tantalum. No surface morphology change of a VPS W coated F82H sample was observed under 10 plasma pulses of ∼0.3 MJ m−2, although surface melting and cracks in the resolidification layer occurred at higher energy density of ∼0.9 MJ m−2. There was no indication of exfoliation of the W coating from the substrate of F82H after the pulsed plasma exposures