Favourable scenarios established by SMBI for the realization of the ELMy H-mode at HL-2A**Project supported by the National Natural Science Foundation of China (Grant Nos. 11375057 and 11175061) and the National Magnetic Confinement Fusion Science Program, China (Grant Nos. 2010GB102003 and 2014GB108003).

Abstract

The ELMy H-mode plasmas realized with the supersonic molecular beam injection (SMBI) are studied in relation to the energy confinement and the heating power for the L–H transition ( in the HL-2A tokamak. A database is assembled for this study based on the ELMy H-mode discharges during the experimental campaigns in the period 2009–2013 at the HL-2A tokamak. The statistical results show that the SMBI is favourable for reaching the H-mode by reducing the heating power at the L–H transition and for the H-mode performance by improving the energy confinement compared with the ordinary gas puffing (GP). The reduction of is about 20% when the density is low, and the energy confinement enhancement factor of 1.5 is achieved with the SMBI. Note that in the database the density dependence of is non-monotonic with the at which the is minimum. Most of data are on the low density branch where the increases with the decrease in density. The minimum of the in HL-2A is comparable to the ITPA multi-machine threshold power scaling . The physics behind the reduction of the with the SMBI is also investigated in relation to the change of the density gradient at the plasma edge, the gas fuelling efficiency, and the recycling.