Tungsten damage and melt losses under plasma accelerator exposure with ITER ELM relevant conditions

Abstract

Experimental simulations of ITER edge-localized mode have been performed with a Kh-50 quasi-stationary plasma accelerator. Heat loads exceeded the tungsten melting threshold. Droplet splashing and the solid dust ejection were observed. Droplets were emitted during the plasma exposure and dust generation dominated after the end of a plasma pulse, at the time of the material cooling. A decrease in the droplet velocity at an increase in the surface heat load was observed. It could be attributed to growing sizes of the droplets at higher energy loads. After one hundred pulses were performed at loads below the tungsten melting and above the cracking threshold, some porosity appeared. Such defects achieved dimensions of several tens of μm. A heat load amounting to half the cracking threshold (0.3 MJ m−2) could lead to the appearance of fatigue cracks after 100 plasma pulses. In this case the appearance of cracks could be caused by the accumulation and redistribution of linear defects (dislocations) in the affected tungsten layer.