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

Asakura, Nobuyuki; Takechi, Manabu; Oyama, Naoyuki; Nakano, Tomohide

Fast sampling diagnostics such as Langmuir probes and magnetic pick-up coils were developed in JT-60U. ELM radial expansion was important to understand the heat and particle load on the first wall. Enhancement and radial expansion of the SOL plasma just after ELM were investigated at Low-Field-Side and High-Field-Side. Ion saturation current () profile was described by two-exponential fit (i.e. 1st and 2nd lgi). Enhancement of the particle flux was different in poloidal location: particle flux profile became very flat, in particular, at HFS. Radial expansion speed at LFS was evaluated in the range of 1-3 km/s. ELM plasma flux in LFS and HFS divertors was investigated. Fast changes of js and floating potential (Vf) were measured. Large negative Vf was observed and durations of the negative js and Vf were 100 ms, which was shorter than heat deposition (250 ms). The large negative js and Vf near both strike-points suggested fast electron deposition rather than thermal electric current. Influence of the divertor sheath on the heat deposition time is discussed.