The penetration characteristics of supersonic molecular beam injection (SMBI) have been studied on the HL-2A tokamak. The signals from the tangential D α array and CCD camera clearly show that the SMBI from the low field side consists of a slow component (SC) and a fast component (FC) because of a small percentage of H 2 present in the D 2 reservoir. The FC can penetrate more deeply than the SC, e.g. 8.5 cm inside the last closed flux surface, while the SC is around 4 cm. The penetration depth of the SMBI is weakly dependent on plasma parameters before injection and its backing pressure. Fuelling efficiency of SMBI is also estimated because it is one of the key issues in fusion plasmas. Typical fuelling efficiency of SMBI is 30-60% for the limiter configuration on the HL-2A tokamak. The variation of the decay time of the post-SMBI electron density is more responsible for the large scatter of the measured fuelling efficiencies than the different injection depths.

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