Predictive modeling of the deuterium gas puffing effect on impurity and heat flux compression for the HL-2M divertor by SOLPS

Abstract

To study the effect of gas puffing on divertor operation regime and impurity level in the SOL region, we introduce deuterium gas puffing and pumping, based on the HL-2M lower single null (LSN) divertor configuration (Ip=2MA), using the SOLPS5.0 code. The simulation result indicates that the location of the gas puffing port impacts the divertor plasma condition, and puffing deuterium from the location near the divertor region can enhance the power dissipation and the divertor regime transformation from high recycling region to detachment. Besides, increasing deuterium gas puffing rate can strengthen the core confinement. Meanwhile, the impurity level in the SOL region is compressed rapidly, from Zeff=2.0 to 1.1, with a reasonable deuterium gas puffing rate of 2.5×1022s−1 puffed from the optimized port and a constant chemical sputtering yield Ychem of 1.0%, compared to the case with no gas puffing. The physics interpretation behind this phenomenon is also analyzed. It is demonstrated that the ionization rate distribution and the carbon ions’ poloidal velocity define the impurity flow in the SOL region. The higher ionized carbon ions (C4+ to C6+) retain in the ionization region and even flow downstream when they finish ionization before reaching the stagnation point with gas puffing. Then the impurity ions accumulate in the divertor region. The balance between the thermal and friction forces acting on the carbon ions results in the change of poloidal velocity. In general, deuterium gas puffing and pumping induces the modification of impurity flow and the decline of the Zeff. Furthermore, a chemical sputtering yield of 3.0% is also calculated to verify the efficiency of deuterium gas puffing on Zeff compression.