(EX/P3-21) Plasma Behavior with Hydrogen Supersonic Molecular Beam and Cluster Jet Injection in the HL-2A Tokamak
1) Southwestern Institute of Physics, Chengdu, China
2) Shanghai Institute of Optics and Fine Mechanics, Shanghai, China
Abstract. The experimental results of low pressure supersonic molecular beam injection (SMBI) into the HL-2A plasma indicated that during the period of SMB pulse injection the power density convected at the divertor target plate surfaces was 0.4 times of that before or after the beam injection. The clusters are produced at nitrogen temperature in a supersonic adiabatic expansion of moderate pressure hydrogen gases into vacuum through a Laval nozzle. The averaged cluster size was measured by Rayleigh scattering as large as hundreds atoms. Multifold diagnostics for the cluster jet injection (CJI) experiments have given a coincident evidence that there was a terminal area where a great deal particles from the clusters deposited at, rather than the clusters uniformly ablating along the injection path. A SMB with large clusters, which are like micro-pellets, was of benefit for deeper fuelling and the fuelling efficiency is distinctly better than that of the room temperature SMBI. Another important effect of the CJI or the high pressure SMBI was that the runaway electrons were cooled down to thermal velocity due to a combination of collision and radiative stopping in such a massive fuelling. So the new fuelling technique may become a good treatment to mitigate fast plasma shutdowns and disruptions.
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