Favourable scenarios established by SMBI for the realization of the ELMy H-mode at HL-2A

Key words: 
• ELMy H-mode /
• SMBI /
• L-H transition /
• energy confinement /
• database

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 (PL-H) 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-ⅡH transition and for the H-mode performance by improving thc cnergy confincmcnt compared with the ordinary gas puffing (GP).The reduction of PL-H is about 20％ when the density is low,and the energy confinement enhancement factor of HH98y2 =τE/τth,98y2 ≈ 1.5 is achieved with the SMBI.Note that in the database the density dependence of PL-H is non-monotonic with the-ne,min ≈ 3× 1019 m 3 at which the PL-H is minimum.Most of PL-H data are on the low density branch where the PL-H increases with the decrease in density.The minimum of the PL-H in HL-2A is comparable to the ITPA multi-machine threshold power scaling Pthr_scal08.The physics behind the reduction of the PL-H 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.