An innovative approach to the improved radiating divertor concept by supersonic molecular beam injection on HL-2A

The 'puff-and-pump' radiating divertor condition is a promising approach for the reduction of excessive thermal power loading on the divertor targets. The divertor supersonic molecular beam injection (SMBI) system installed on HL-2A strongly enhances the capacity of the divertor heat load control. This system has a faster time response than the divertor gas puffing (GP) system. Divertor heat load control capacity has been compared between these two techniques by experiments on HL-2A and simulations. Experimental results suggest that the divertor SMBI system reduces the divertor heat flux peak to a lower level with less time delay than that for the divertor GP system, owing to a higher injection rate and particle velocity. Simulations by SOLPS demonstrate that a high injection rate shortens the function time which is defined by the time interval between the arrival of the particles at the divertor plasma edge and the reduction of divertor electron temperature. High velocity of SMBI injected neutral gas particle also shortens the particle flight time to arrive at the edge. Less flight time and function time lead to a faster response of the divertor SMBI system compared to the divertor GP system. In addition, simulations by EMC3-EIRENE also suggest that, compared to the GP system, stronger heat load reduction of the SMBI system can also be caused by deeper deposition of gas source owing to its higher particle velocity.