Visible spectrometer at the Compact Toroid Injection Experiment and the Alcator C-Mod tokamak for Doppler width and shift measurements

A novel Doppler spectrometer is currently being used for ion or neutral velocity and temperature measurements on the Alcator C-Mod tokamak. The spectrometer has an f∕# of ∼3.1 and is appropriate for visible light (3500–6700A). The linewidth from a line emitting calibration source has been measured to be as small as 0.4A. The ultimate time resolution is line brightness light limited and on the order of milliseconds. A new photon efficient charge coupled device detector is being used at C-Mod. Time resolution is achieved by moving the camera during a plasma discharge in a perpendicular direction through the dispersion plane of the spectrometer, causing a vertical streaking across the camera face. Initial results from C-Mod as well as previous measurements from the Compact Toroid Injection Experiment are presented.