The role of particle sinks and sources in Alcator C-Mod detached divertor discharges

Detailed measurements of the magnitude and location of volumetric recombina tion occurring in the detached divertor of Alcator C-Mod tokamak [I. H. Hut chinson et al., Phys. Plasmas 1, 1511 (1994)] are presented. The drop in di vertor plate ion current during detachment is due to two mechanisms: (1) vo lumetric recombination in the divertor plasma; and (2) reductions in the di vertor ion source. Depending on plasma conditions, each of these can be the primary mechanism for the observed ion current reduction in detachment. Th e ion source during detachment is inferred and its magnitude is consistent with the measured divertor power flow. A scaling of the density in the dive rtor recombining region for L- (low confinement) mode plasmas is found, n(e ,r)proportional to (n) over bar(e)(0.8).P-SOL(2/7). A model based on pressu re variation along a flux surface during detachment is consistent with the main features of this scaling. (C) 1999 American Institute of Physics. [S10 70-664X(99)93505-X].