Boswell, C. J., Terry, J. L., Lipschultz, B., PSFC, MIT
A two-CCD camera system is currently employed on Alcator C-Mod. It has the capability of recording visible emission from both a wide-angle view of the plasma and, with a higher spatial resolution, the divertor region. The cameras selectively view a single spectral line (\(D_{\alpha}\), \(D_{\beta}\), or \(D_{\gamma}\)) through the use of filters placed in front of the cameras' lenses. The divertor-viewing camera uses interference filters, while the wide-angle view uses glass absorption filters. The cameras are calibrated, allowing for absolute brightness measurements. Using the camera-recorded brightnesses and the assumption of toroidal symmetry, reconstructions of 2-D absolute emissivity profiles are generated. Using these profiles we have investigated the 2-D shape evolution of deuterium emission in the divertor and of midplane MARFEs. For example, we find that during divertor detachement the emission moves away from the strikepoint and spreads out along the separatrix between the x-point and the strikepoint. The process and assumptions required to generate these reconstructions and their use in calculating recombination in diverted operation and in the midplane MARFE will be discussed.
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