Surface modification and droplet formation of tungsten under hot plasma irradiation at the GOL-3

The paper presents experimental investigations of tungsten surface modification after plasma loads at the multimirror trap GOL-3. Energy loads on tungsten surface varied from 2 up to 4MJ/m2 per shot with sets from 1 to 9 repetitive irradiations that corresponds to loads higher than tungsten melting threshold and is close to ITER giant ELM loads. Targets surface modification and transverse microsections after irradiation was studied by optical microscopy, SEM and hardness tester. Formation on tungsten surface of three different crack networks with typical cell sizes of 1000, 10 and 0.3μm and bubbles are identified. The network of large cracks extend perpendicularly to the irradiated sample surface to a depth of 50–350μm. Erosion depth depends on energy loads – rises from 20 to 200μm at 2 and 4MJ/m2 correspondingly. Cracking, development of tungsten surface morphology and droplets splashing are discussed.