Investigation of edge localized mode in the JFT-2M tokamak

The edge localized mode (ELM) was investigated in detail on the JFT-2M tokamak. Spatially, a pivot point was observed inside the separatrix flux surface. Temporally, an ELM event starts from the precursor oscillation, of which the growth rate was about 40 mu s. Another high frequency oscillation with about 300 kHz was found during the magnetic fluctuation burst. Just after the burst, a poloidal electric current (ELM current) was induced in the scrape-off layer. During the ELM, the particle flux to the divertor plates was transiently enhanced by a factor of about 4. The profile of the induced flux was 2-3 times broader than that in the ELM-free period. The total particle flux induced by one ELM was evaluated to be about 5% of the total plasma particles. The ELM current is characterized by its direction and its large fluctuation level. Furthermore, it was found that a large opposite current exists near the strike points on both divertor plates