Dissipative Divertor Operation in the Alcator C-mod Tokamak Dissipative Divertor Operation in the Alcator C-mod Tokamak

The achievement of large volumetric power losses (dissipation) in the Alcator C-Mod divertor region is demonstrated in two operational modes: radiative divertor and detached divertor. During radiative divertor operation, the fraction of SOL power lost by radiation is P R/PSOL0.8 with single null plasmas, n e < 2x10 20 m-3 and I < 1 MA. These plasmas sometimes have very high recycling, with nediv : 6 x 1020 m-3. As the divertor radiation and density increase, the plasma eventually detaches abruptly from the divertor plates: ISAT drops at the target and the divertor radiation peak moves to the x-point region. Probe measurements at the divertor plate show that the transition occurs when Te ~ 5 eV. The critical ne for detachment depends linearly on the input power. This abrupt divertor detachment is preceded by a comparatively long period (~1-200 ms) where a partial detachment is observed to grow at the outer divertor plate.