COMPARISON OF DETACHED AND RADIATIVE DIVERTOR OPERATION IN ALCATOR C-MOD

The divertor of the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511 (1994 )] routinely radiates a large fraction of the power entering the scrap e-off layer. This dissipative divertor operation occurs whether the di vertor is detached or not, and large volumetric radiative emissivities , up to 60 MW m(-3) in ion cyclotron range of frequency (ICRF) heated discharges, have been measured using bolometer arrays. An analysis of both Ohmic and ICRF-heated discharges has demonstrated some of the rel ative merits of detached divertor operation versus high-recycling dive rtor operation. An advantage of detached divertor operation is that th e power flux to the divertor plates is decreased even further than its already low value. Some disadvantages are that volumetric losses outs ide the separatrix in the divertor region are decreased, the neutral c ompression ratio is decreased, and the penetration efficiency of impur ities increases. (C) 1996 American Institute of Physics.