Applications of visible CCD cameras on the Alcator C-Mod tokamak

Abstract

Five 7 mm diameter remote-head visible charge-coupled device (CCD) cameras are being used on Alcator C-Mod for several different diagnostic purposes. All of the cameras’ detectors and optics are placed inside a magnetic field of up to 4 T. Images of the cameras are recorded simultaneously using two three-channel color framegrabber cards. Two CCD cameras are used typically to generate two-dimensional emissivity profiles of deuterium line radiation from the divertor. Interference filters are used to select the spectral line to be measured. The local emissivity is obtained by inverting the measured brightnesses assuming toroidal symmetry of the emission. Another use of the cameras is the identification and localization of impurity sources generated by the ion cyclotron radio frequency (ICRF) antennas, which supply the auxiliary heating on Alcator C-Mod. The impurities generated by the antennas are identified by correlating in time the injections seen at the cameras with measurements made with core diagnostics. Fibers whose views aligned with the camera views and whose outputs are coupled to a visible spectrometer are also used to identify the species of the impurities injected.