Effect of preheating on the damage to tungsten targets after repetitive ITER ELM-like heat loads

The behaviour of a preheated tungsten target under repetitive pulsed plasma impacts of the energy density 0.75 MJ m −2 with the pulse duration of 0.25 ms was studied with the quasi-stationary plasma accelerator (QSPA) Kh-50. Two identical samples of pure sintered tungsten have been exposed to numbers of pulses exceeding 100. One sample was maintained at room temperature and the other sample preheated at 650 °C. The experiments demonstrated that on the cold surface some macro-cracks dominate, but on the hot surface they do not develop. However, in both cases some fine meshes of micro-cracks are observed. With increasing the number of exposures, the width of the micro-cracks gradually increases, achieving 0.8–1.5 μm after 100 pulses. In addition, the SEM shows some cellular structure with the cell sizes about 0.3 μm, and after large numbers of exposures some blisters of sizes up to 100–150 μm appear.