Tungsten erosion under plasma heat loads typical for ITER type I ELMS and disruptions

The behavior of pure sintered tungsten under repetitive plasma heat loads of similar to 1 Mj/m(2) (which is relevant to ITER ELMs) and 25 MJ/m(2) (ITER disruptions) is studied with the quasi-steady-state plasma accelerator QSPA Kh-50. The ELM relevant heat loads have resulted in formation of two kinds of crack networks, with typical sizes of 10-20 mu m and similar to 1 mm, at the surface. Tungsten preheating to 660 degrees C indicate, that fine intergranular cracks are probably caused by thermal stresses during fast resolidification of the melt, whereas large cracks are the result of ductile-to-brittle transition. For several hundreds of ELM-like exposures, causing surface melting, the melt motion does not dominate the profile of the melt spot. The disruption relevant experiments demonstrated that melt motion became the main factor of tungsten damage. (c) 2004 Elsevier B.V. All rights reserved.