Characteristics and control of the Type I edge localized mode in JT-60U

Oyama, Naoyuki; Hayashi, Nobuhiko; Aiba, Nobuyuki; Isayama, Akihiko; Urano, Hajime; Sakamoto, Yoshiteru; Kamada, Yutaka; Takizuka, Tomonori; JT-60 Team

Coherent density and temperature precursors have been observed before the collapse phase of the Type I ELM. The growth rate of the precursor is evaluated to be for several edge pedestal conditions. From the phase delay between ECE signals measured at two toroidal locations and the frequency of the precursor, the toroidal mode number is evaluated as n = 8-10 or 14-16. It is found that the dominant n varies with each ELM under the same plasma condition. When the ratio of the pressure gradient inside the pedestal to the pressure gradient within the pedestal becomes large, larger reduction of ion temperature as well as wider ELM affected area has been observed. When the plasma near the top of the pedestal on the high-field side is heated by the electron cyclotron wave power of 1.57 MW, the normalized ELM energy loss was reduced by 33 %, together with the increase in the ELM frequency.