Abstract
Operational density regime of long pulse discharges heated by neutral beam injection (NBI) alone on the large helical device (LHD) is greatly extended by the replacement of stainless steel (SS) divertor plates with graphite tiles resulting in a remarkable reduction of metal impurity radiation. The plasma density can be controlled by gas puffing up to 6×10 19 m −3 . Particle balance is analyzed by a global particle balance equation for helium and hydrogen discharges with high density. For helium discharges, the plasma particle inventory can be almost completely accounted for by the integrated gas puff input. A strong wall pumping is observed for hydrogen only discharges and it is found that the recycling coefficient at the start-up of the discharge is less than 0.6. The recycling coefficient increases with the wall particle inventory and approaches unity for high wall loading (23 Pa m 3) .
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