Evolution of tungsten degradation under different cyclic ELM-like high heat flux plasma

Abstract

A millisecond pulsed repetitive plasma generator based on capillary discharge is utilized to produce ELM-like heat load. Based on this device, the evolution of tungsten degradation under heat loads with different heat fluxes, pulses, and frequencies is investigated. With an increase of heat flux and pulse, the tungsten surface experiences an increasing melting and cracking damage. The cross-sections of samples are analyzed to investigate the mechanisms of crack formation and propagation. There are numerous small cracks of ∼20 μm length in the melting layer, which may extend to form the primary cracks under further stress. Among the primary cracks, the central crack in the heat-affected layer initially propagates perpendicularly to the surface and grows parallel to the surface, converging with the edge cracks under cyclic high heat loads. And the microstructures near cracks also reveal the mechanism of crack formation, including the intergranular primary cracks and partial transgranular secondary cracks. This work provides a novel approach to simulating ELM-like thermal load and corresponding tungsten cracking behavior under repetitive high heat flux plasma.