Helium exhaust in ELMy H-mode plasmas with W-shaped pumped divertor of JT-60U

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. The He fueling rate by He beam injection was balanced with He pumping. In steady state, good He exhaust capability was successfully demonstrated in attached ELMy H-mode plasmas. A global particle confinement time of τ* He=0.7 s and τ* He/ τ E=4 ( τ E: the energy confinement time) was achieved in attached plasmas, well within the range generally considered necessary for successful operation of a future fusion reactor, such as ITER. The enrichment factor of He was obtained to be about 1.0, which is five times larger than the ITER requirement of 0.2. 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.