2-D images of deuterium emission in the Alcator C-Mod tokamak divertor

Two 7-mm diameter, remote-head, visible, charge-coupled device (CCD) cameras are used on the Alcator C-Mod tokamak to generate two-dimensional emissivity profiles of deuterium line radiation (typically at Balmer /spl alpha/ and Balmer /spl gamma/) from the divertor. These emissivity profiles are obtained by reconstructing the measured brightnesses using the thin-chord approximation and assuming toroidal symmetry of the emission. The regions of the divertor with a high ratio of Balmer /spl gamma/ to Balmer /spl alpha/ emission are indicative of a plasma that is recombining. These recombining regions in the divertor are seen to shift from the inner to the outer divertor as the core density in increased.