Divertor heat flux reduction by D2 injection in DIII-D

D2 gas injected into ELMing H-mode discharges in DIII-D reduced the total integrated heat flux to the divertor ≅ 2x and the peak heat flux ≅ 5x, with only modest degradation to plasma stored energy. Steady gas injection without particle pumping results in eventual degradation in stored energy. The initial reduction in peak heat flux at the divertor tiles may be primarily due to the increase in radiated power from the X-point/divertor region. The eventual formation of a high density region near the X-point appears to play a role in momentum (and energy) transfer from the flux surfaces near the outboard strike point to flux surfaces farther out into the scrape-off. This may also contribute to further reduction in peak heat flux. (orig.)