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(EX6/5) Steady-State Exhaust of Helium Ash in the W-Shaped Divertor of JT-60U

A. Sakasai, H. Takenaga, N. Hosogane, H. Kubo, S. Sakurai, N. Akino, T. Fujita, S. Higashijima, H. Tamai, N. Asakura, K. Itami, K. Shimizu and the JT-60 Team

Japan Atomic Energy Research Institute, Naka Fusion Research Establishment Naka-machi, Naka-gun, Ibaraki-ken, 311-0193 Japan

Abstract.  By injecting a neutral beam of 60 keV helium (He) atoms as central fueling of helium into the ELMy H-mode plasmas, helium exhaust has been studied in the W-shaped pumped divertor on JT-60U. Efficient He exhaust was realized by He pumping using argon frosted cryopumps in the JT-60U new divertor. In steady state, good He exhaust capability ( $\tau^{*}_{\mathrm{He}}$/$\tau_{\mathrm{E}}^{}$ = 4 and high enrichment factor, where $\tau^{*}_{\mathrm{He}}$ is a global particle confinement time of helium and $\tau_{\mathrm{E}}^{}$ is the energy confinement time) was successfully demonstrated in attached ELMy H-mode plasmas. Good He exhaust capability was also obtained in detached ELMy H-mode plasmas, which was comparable to one in attached plasmas. This result of the helium exhaust is sufficient to support a detached divertor operation on ITER. After the divertor modification, helium exhaust in reversed shear plasmas has been investigated using He gas puff. Helium removal inside the internal transport barrier (ITB) is about two times as difficult as that outside the ITB in reversed shear discharges.

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