Plasma-Surface Interaction during ITER Type 1 ELMs: Comparison of Simulation with QSPA KH-50 and the GOL-3 Facilities

Abstract

The paper presents experimental investigations of plasma-surface interaction and materials behavior under plasma loads relevant to type I ITER ELMs. The experiments were performed with quasi-stationary plasma accelerator QSPA Kh-50 and multi-mirror trap GOL-3 devices located in Kharkov (Ukraine) and Novosibirsk (Russia) respectively. QSPA generated repetitive plasma streams of duration 0.25 ms and the energy density up to 2.5 MJ/m². In GOL-3 multi-mirror trap plasma was heated up to temperature of 2-4 keV by a high power relativistic electron beam. Energy density in the exhaust plasma stream vary from 0.5 to 30 MJ/m². Surface patterns of the targets exposed by QSPA and GOL-3 plasma are analyzed. Cracking, development of tungsten surface morphology and droplets splashing are discussed. It is shown that under an applied energy density loads (>1 MJ/m²) the evolution of surface morphology due to plasma irradiation are similar for two devices in spite of the qualitative differences of particles energy of the impact plasma streams. Formation of three different crack networks with typical cell sizes of 1000, 10 and 0.3 μm are identified after irradiation of tungsten surface. Experiments show that major cracks (cell size of 1000 μm) are attributed to a ductile-to-brittle transition. The key role of heat loads magnitude on development of surface due to powerful plasma impacts is demonstrated.