Fuelling Efficiency and Penetration of Supersonic Molecular Beam Injection in HL-2A Tokamak Plasmas

Full text: The penetration characteristics of supersonic molecular beam injection (SMBI) have been studied on the HL-2A tokamak. The signals from the tangential Dα array and CCD camera clearly show that the SMBI from low field side (LFS) consists of a slow component (SC) and a fast component (FC). The FC can penetrate more deeply than the SC, such as 8.5 cm inside the last closed flux surface (LCFS), while the SC penetration is around 4 cm. The penetration depth of the SC is weakly dependent on the line-averaged plasma density before injection and its backing pressure. The typical fuelling efficiency of LFS SMBI is 30 ∼ 60% for the limiter configuration. It is more the variation of the decay time of the post-SMBI electron density than the different injection depth that is responsible for the large scatter of the measured fuelling efficiencies. The fuelling efficiency and response of plasma to injection are compared among Gas puffing (GP), LFS and HFS SMBIs. The fuelling efficiency from high field side (HFS) is higher than that from LFS for the Ohmic heating discharges; moreover, with ECRH power of 1.3 MW, this trend becomes much more distinct indicating it is better for SMBI to fuel from HFS. And the LFS SMBI features relatively high fuelling efficiency and low perturbation to plasma. (author)