Abstract
Pellet injection has been used as a primary fuelling scheme in the Large Helical Device.
With pellet injection, the operational region of NBI plasmas has been extended to higher densities
while maintaining a favourable dependence of energy con nement on density, and several important
values, such as plasma stored energy of 0.88 MJ, energy con nement time of 0.3 s, of 2.4% at 1.3 T
and density of 1:11020 mô€€€3, have been achieved. These parameters cannot be attained by gas pung.
Ablation and the subsequent behaviour of the plasma have been investigated. The measured pellet
penetration depth estimated on the basis of the duration of the H emission is shallower than the
depth predicted from the simple neutral gas shielding (NGS) model. It can be explained by the NGS
model with inclusion of the e ect of fast ions on the ablation. Just after ablation, the redistribution
of the ablated pellet mass was observed on a short timescale (400 ms). The redistribution causes
shallow deposition and low fuelling eciency.
