A new fueling method for fusion plasma. Supersonic molecular beam injection

A new method of gas fueling--pulsed supersonic molecular beam injection (MBI), has been introduced in the HL-1M tokamak. Its performance is something between gas puffing (GP) and the pellet injection. The well-collimated hydrogen beam has a velocity of about 500 m·s-1. With a penetration depth of hydrogen particles (1/e decay) ≥10 cm, the ramp-up rate of electron density dne-bar/dt is as high as 2.9 x 1020 m-3·s-1 without disruption and the resulted plasma density reaches ne-bar = 8 x 1020 m-3 with reduced impurity concentration. The profile peaking factor Qn after MBI reaching a maximum value is larger than 1.65. With MBI the energy confinement time τE measured by diamagnetism is 10%-30% longer than that with GP under same discharge conditions