Achievement of Helium Exhaust Performance for ITER
JT-60 started operating with a new W-shape pumped divertor configuration like ITER in June 1997. Recently, a necessary condition to purify the plasma for sustained self-ignition in ITER has been demonstrated during an ELMy H-mode which is considered as a standard operation mode in ITER.
In ITER, helium ash pro-duced from fusion reac-tions should be less than 10% of the electron density to sustain the ignition condi-tion. Consequently, the ratio of effective helium pumping time to energy confinement time is required to be below 10.
The present result has been obtained from an advanced experimental scheme (Fig.1), in which energetic helium beams are injected into the central plasma for a duration suffi-ciently longer than the he-lium pumping time (~0.7 s) to simulate the production and exhaust of helium ash in a reactor core plasma.
The helium density is maintained at a low level as shown in Fig.2 with its ratio of ~4. Sufficiently meeting the requirement from ITER,the helium exhaust per-formance has been demon-strated in JT-60.
Fig.1 Experimental set up
Fig.2 Time evolution of helium density in the plasma