Parallel and radial transport of ELM plasma in the SOL and divertor of JT-60U

Abstract

Parallel and radial transport of ELMs in the Scrape-Off-Layer and divertor were investigated in JT-60U. The time lag from the start of magnetic fluctuations to the peak of the ion saturation current (js) at low-field-side (LFS) divertor was consistent with convective transport of the ELM plasma along field lines. However, the time lag to the start of the js enhancement was shorter than the convection time between the LFS midplane and divertor. In addition, js started to increase both at high-field-side and LFS divertors simultaneously, which is not explained by the convection model. Large multi-peaks appeared in the time traces of js at the midplane and near the X-point. The radial distribution of the first peak show that the ELM particle flux is transported to outer SOL flux surfaces up to 15cm from the separatrix. The radial expansion speed at the midplane was in the range of 1–2.5km/s.