The effect of divertor baffling on Alcator C-Mod discharges

The effect of divertor baffling on Alcator C-Mod [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] discharges has been investigated using a novel dive rtor bypass. The bypass allows the in situ variation of the mechanical cond uctance from the divertor plenum to the main chamber between or even during discharges. The results indicate a strong dependence on baffling for the c ompression of deuterium and recycling impurity gases in the divertor plenum in a variety of C-Mod discharges, indicating that tight baffling would be desirable in a future tokamak reactor. There is no apparent effect of the d ivertor baffling for the Ohmic, L-mode and EDA (Enhanced D-alpha) H-mode di scharges in this study on main chamber neutral particle populations, scrape -off-layer flows, nonrecycling impurity screening, global energy confinemen t or H-mode threshold powers. (C) 2000 American Institute of Physics. [S107 0-664X(00)94405-7].