Comparison between supersonic molecular-beam injection and conventional gas-puffing for plasma performance in Heliotron J

Fueling control with a supersonic molecular-beam injection (SMBI) technique is examined in Heliotron J comparing with conventional gas-puffing. The supersonic H2-beam is injected from a fast valve with a conic nozzle and the apparent fueling efficiency is estimated to be about 50-60% for NBI and 20-30% for ECH + NBI discharges with n¯e ∼ 1 × 1019 m−3. In a combination heating of ECH and NBI, the stored energy reached ∼4.5 kJ, which is about 50% higher than the maximum one achieved so far under the similar heating condition with conventional gas-puffing in Heliotron J. Although a short pulse of intense gas-puff can also produce a rapid increase of n¯e like the SMBI case, the n¯e-Wp dependence cannot overcome the saturation in higher density region.