Fast measurement of ELM heat and particle fluxes, and plasma flow in the scrape-off layer of the JT-60U tokamak

Abstract

The transport process of ELM heat and particle fluxes responsible for the rapid plasma deposition on the divertor target was investigated. The scrap-off layer (SOL) plasma flow driven along the field lines was measured in the ELMy \\mbox{H-mode} plasma, for the first time, at three important locations (i.e. outer midplane, x-point and high-field-side SOL) using electrostatic probes (Mach probe) on the JT-60U tokamak. The radial profiles of the plasma flow were determined. Just below the x-point of the low-field-side SOL, a rapid increase in the flow velocity up to the ion sonic level was observed during 200-300 µs after ELM events, and the radial width was 1.0-1.5 cm (mapping to the midplane SOL). The duration and width of the rapid plasma flow were comparable to the deposition duration and width of the heat load to the outer divertor target measured with an infrared TV camera (250 µs time resolution). A simple model analysis showed that convective transport gives a large contribution to the ELM heat deposition process. On the other hand, at the high-field-side SOL, SOL flow towards the inner divertor was not observed after ELM events. The ELM heat and particle fluxes in the high-field-side SOL were not explained by the simple convective transport model.