Fast dynamics of type I and grassy ELMs in JT-60U

Kojima, Atsushi; Oyama, Naoyuki; Sakamoto, Yoshiteru; Kamada, Yutaka; Urano, Hajime; Kamiya, Kensaku; Fujita, Takaaki; Kubo, Hirotaka; Aiba, Nobuyuki; JT-60 Team

In order to understand the physics of the ELM trigger and determining the ELM size, the fast ELM dynamics of type I and grassy ELMs have been studied in JT-60U, using new fast diagnostics with high spatial and temporal resolutions. The evolution of the ion pressure profile in the pedestal region is evaluated for the first time by detailed edge profile measurements. Type I ELMs observed in co-rotating plasmas exhibited larger and wider ELM affected area than ctr-rotating plasmas. Just before type I ELM crash, the pedestal ion pressure and its maximum gradient in co-rotating plasmas are 20% and 12% higher than those in ctr-rotating plasmas, respectively. It is found that the radial extent of the ion pressure gradient at the pedestal region in co-rotating plasmas is 14% wider than that in ctr-rotating plasmas. The experimental results suggest that the ELM size is determined by the structure of the plasma pressure in the whole pedestal region.