Edge pedestal characteristics in JET and JT-60U tokamaks under variable toroidal field ripple

Urano, Hajime; Saibene, G.*; Oyama, Naoyuki; Parail, V.*; de Vries, P.*; Sartori, R.*; Kamada, Yutaka; Kamiya, Kensaku; Loarte, A.*; Lnnroth, J.*; Sakamoto, Yoshiteru; Salmi, A.*; Shinohara, Koji; Takenaga, Hidenobu; Yoshida, Maiko; JT-60 Team; JET-EFDA Contributors*

The effect of TF ripple on the edge pedestal characteristics are examined in JET and JT-60U. By the installation of ferritic inserts, TF ripple was reduced from to in JT-60U. In JET, TF ripple was varied from to by feeding different currents to TF coils. The pedestal pressure was similar with reduced ripple in JT-60U. In JET, no clear difference of the pedestal characteristics was also observed. The edge toroidal rotation clearly decreased in counter direction by increased TF ripple. However, in JT-60U, the ELM frequency decreased by and the increased ELM loss power by with reduced ripple. In JET, ELM frequency increases only slightly with increased TF ripple. From this inter-machine experiment, TF ripple less than does not strongly affect the pedestal pressure. The effect of TF ripple on pedestal characteristics at lower collisionality close to ITER should be investigated as a next step study.