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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
= 0.4s and
/
= 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.
IAEA 2001