Spectroscopy of Plasma Surface Interaction in Experiments Simulating ITER Transient Events

Abstract

This report presents the results of experimental studies of powerful plasma impacts upon tungsten and carbon surfaces, which are ITER relevant Plasma Facing Materials (PFMs). The simulation experiments were carried out with a QSPA Kh-50 (Quasi-Stationary Plasma Accelerator) in Kharkov Institute of Physics and Technology (Ukraine) and an RPI-IBIS (Multi-Rod Plasma Injector) facility in the Andrzej Soltan Institute for Nuclear Studies (IPJ) Swierk (Poland).QSPA Kh-50 generates hydrogen plasma streams of duration of 0.25 ms and the heat loads in the range of 0.2–2.5 MJ/m2, which correspond to the Edge Localized Modes (ELM) impacts expected in ITER. The plasma stream diameter is 18 cm, averaged ion energy is about 0.4 keV, and the maximum plasma pressure achieves 3.2 bar. Due to that fact, using the QSPA Kh-50 it is possible to simulate ITER transient events. Deuterium plasma streams with power density of 10-50 W/m2 and pulse duration of 1-5 μs, generated by RPI-IBIS were used for comparative studies and determination of an initial stage of evaporated impurities dynamics during plasma-surface interactions as well as features of surface damages appearing under varied plasma parameters.In order to determinate the main plasma parameters (an electron density and temperature) and to study of impurities behavior at the time of discharge the use was made of optical spectroscopy methods. The onset of a vapor shield in front of the target surface was investigated in dependence on a surface heat load for tungsten (W) and carbon (C) targets. Information about dynamics of the W- and C-ions production was obtained.Some issues of the droplet splashing at the tungsten surfaces and the formation of hot spots upon the graphite surface, which can be sources of the enhanced evaporation, are also discussed.