MODIFICATION AND CONTROL OF DIVERTOR DETACHMENT IN ALCATOR C-MOD

The effect of adding different impurity gases and ICRF heating on dive rtor detachment has been compared for Ohmic, L-mode and high-q(paralle l to) (greater than or equal to 300 MW/m(-2)), H-mode plasmas. The rel ative effect of all these external controls on divertor and core radia tion is evaluated. Recycling gases (Ne and Ar) are found to primarily affect the main plasma as opposed to the divertor region. The lower Z non-recycling gases, N-2 and CD4 are more efficacious in this regard. N-2 was found effective in inducing detachment for high-q(parallel to) , H-mode plasmas. An additional advantage of N-2 over the higher Z gas es is that its injection resulted in the smallest degradation in H-mod e energy confinement (similar to 10%).