The W-shaped divertor of JT-60U was modified from inner-leg pumping to both-leg pumping. After the modification, the pumping rate was remarkably improved with both-leg pumping in a divertor-closure configuration, which means both separatrixes close to the divertor slots. In steady state, efficient helium exhaust was realized in a divertor-closure configuration with both-leg pumping in ELMy H-mode plasmas. A global particle confinement time of τ*He = 0.4 s and τ*He/τE = 3 was achieved in attached plasmas, well within the range generally considered necessary for successful operation of a future fusion reactor, such as ITER-FEAT. The helium exhaust efficiency in the divertor-closure configuration was extended by 45% as compared to the one with inner-leg pumping. In the high X-point configuration with both-leg pumping, the helium exhaust efficiency and the pumping rate of deuterium deteriorated because of the backflow through the outer slot.
Sakasai, A., Takenaga, H., Kubo, H., Akino, N., Higashijima, S., Sakurai, S., … Asakura, N. (2001). Helium exhaust in divertor-closure configuration with W-shaped divertor of JT-60U. Journal of Nuclear Materials, 290–293, 957–961. https://doi.org/10.1016/S0022-3115(00)00473-6