A new method of gas fuelling, pulsed supersonic molecular beam injection(SMBI), has been successfully developed and used in the HL-1M tokamak. SMBI is anattempt to enhance the penetration depth and the fuelling efficiency, as well as to reduce boththe injected particle-wall surface interaction and the impurity content in the plasma.SMBI can be considered a significant improvement over conventional gas puffing. Witha penetration depth of hydrogen particles greater than 15 cm, the rate of increase ofelectron density, de/dt, was up to 7.2 × 1020m-3 s-1without disruption, and the highest plasma density was e = 8.2 × 1019 m-3.The density profile peaking factor Qn reached a maximum value of more than 1.67 afterSMBI. The energy confinement time τE measured by diamagnetism is 10-30% longer thanthat with gas puffing with the other discharge conditions kept the same. SMBI hasrecently been improved to enhance the flux of the beam and to allow a survey of the cluster effect within the beam. A series of new phenomena show the interaction of the beam (includingclusters) with the toroidal plasma, which indicates that hydrogen clusters may beproduced in the beam according to the Hagena empirical scaling law of clustering onset,Γ* = kd0.85P0/T02.29. If Γ* > 100, clusters will form. In thepresent experiment Γ* is about 127.
Penetration characteristics of supersonic molecular beam injection on HL-2A tokamak