PFC / JA - 96 - 20 Modification and Control of Divertor

The effect of adding different impurity gases and ICRF heating on divertor detachment has been compared for ohmic, L-mode and high-q11 ( 300 MW/ m), H-mode plasmas. The relative effect of all these external controls on divertor and core radiation is evaluated. Recycling gases (Ne and Ar) are found to primarily affect the main plasma as opposed to the divertor region. The lower-Z nonrecycling gases, N 2 and CD4 are more efficacious in this regard. N 2 was found effective in inducing detachment for high-q11, H-mode plasmas. An additional advantage of N 2 over the higher-Z gases is that its injection resulted in the smallest degradation in H-mode energy confinement (-10%).