Helium Exhaust and Forced Flow Effects with Both-leg Pumping in W-shaped Divertor of JT-60U
A. Sakasai, H. Takenaga, S. Higashijima, H. Kubo, T. Nakano, H. Tamai, S. Sakurai, N. Akino, T. Fujita, N. Asakura, K. Itami, K. Shimizu, the JT-60 Team
Japan Atomic Energy Research Institute, Naka Fusion Research Establishment Naka-machi, Naka-gun, Ibaraki-ken, 311-0193 JAPAN
Abstract.
The W-shaped divertor of JT-60U was modified from inner-leg pumping to both-leg pumping. After the modification, the pumping rate was improved from 3% with inner-leg pumping to 5% with both-leg pumping in a divertor-closure configuration, which means both separatrixes close to the divertor slots. Efficient helium exhaust was realized in the divertor-closure configuration with both-leg pumping. A global particle confinement time of t*He = 0.4 s and t*He/tE = 3 was achieved in attached ELMy H-mode plasmas. The helium exhaust efficiency with both-leg pumping was extended by 45% as compared with inner-leg pumping. By using central helium fueling with He-beam injection, the helium removal from the core plasma inside the internal transport barrier (ITB) in reversed shear plasmas in the divertor-closure configuration was investigated for the first time. The helium density profiles inside the ITB were peaked as compared with those in ELMy H-mode plasmas. In the case of low recycling divertor, it was difficult to achieve good helium exhaust capability in reversed shear plasmas with ITB. However, the helium exhaust efficiency was improved with high recycling divertor. Carbon impurity reduction was observed by the forced flow with gas puff and effective divertor pumping.