Fueling efficiency of gas puffing on large helical device

Fueling efficiency of gas puffing has been estimated for the net current free plasmas heated by the neutral beam injection in LHD. The particle balance has been analyzed in the latter phase of the density ramp up discharges. The increase rate of the plasma density is correlated to the particle flux of gas puffing alone and not to the other parameters such as the recycling flux, at that phase. The fueling efficiency of 12% has been obtained with this method. The fueling efficiency obtained by this method is insensitive to the heating power or the existence of the magnetic island.