C. J. BOSWELL, J. L. TERRY, B. LIPSCHULTZ, J. A. GOETZ, B. LABOMBARD - PSFC, MIT
Alcator C-Mod currently employs a tangentially viewing divertor TV system consisting of two remote-head CCD cameras with nearly identical views. The cameras are filtered for D$_{\alpha}$ and D$_{\gamma}$ and are simultaneously recorded using a frame grabber card installed on a PC. The recorded images are tomographically inverted assuming toroidal symmetry, using the conjugate-gradient method, into 2-D emissivity profiles. Visible and vacuum ultra-violet spectrometers are used to determine electron density and temperature in the emission region. With these densities, temperatures, emissivities, and a collisional-radiative model of the deuterium population densities, profiles of volume recombination are generated. Evolution of the volume recombination profile in detached L-mode on Alcator C-Mod has been studied, with the following characteristics -- 1) the inner target of the divertor is nearly always detached, 2) as the "depth" of the detachment is increased on outer divertor target the recombining region increasing up the leg until a MARFE is generated inside the separatrix, directly above the x-point, 3) a recombining region exists in the private flux directly below the x-point until detachment begins.