Hydrogen cluster-like behaviour during supersonic molecular beam injection on the HL-1M tokamak

Pulsed supersonic molecular beam injection (SMBI) has been developed successfully and used in the HL-1M tokamak. It is an attempt to enhance the penetration depth and fuelling efficiency. With a penetration depth of hydrogen particles beyond 8 cm, the rising rate of electron density, dn-bare/dt, was up to 7.6x1020m-3·s-1 without disruption, and reached the highest plasma density n-bare=8.2x1019m-3 on HL-1M. With SMBI the plasma energy confinement time, τE, measured by diamagnetism is 10-30 % longer than that with gas puffing when other discharge conditions are kept the same. The fuelling method of SMBI has recently been improved to make a survey of the cluster effects within the beam. A series of new phenomena show the interaction of the beam (including clusters) with the toroidal plasma. Hydrogen clusters may be produced 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 the present experiment Γ* is about 127. (author)