Wavelength calibration of the charge exchange recombination spectroscopy system on the DIII-D tokamak

A wavelength calibration of all the detectors on the charge exchange recomb ination spectroscopy system is performed after every plasma discharge on th e DIII-D tokamak. This is done to insure that the rest of the wavelength po sition of the C VI 5290.5 Angstrom charge exchange line on the detector is accurately known so that the Doppler shift of the spectral line emitted dur ing the discharge can be used for measurements of plasma rotation. In addit ion, this calibration provides a check on the spectral dispersion needed to determine the ion temperature. The reference spectra for the calibration a re Ne I lines created by neon capillary discharge lamps contained within sp ecially designed diffuse reflectors. The Ne I lines at 3520.4720, 5274.0393 , 5280.0853, 5298.1891, and 5304.7580 Angstrom are used in this work. The l ocation of these lines on the linear detectors can be determined to an accu racy of 0.1 pixel, which corresponds to a plasma rotation accuracy of 1.2 a nd 0.7 km/s for the central and edge rotation measurements, respectively. U se of oppositely directed views of the plasma at the same major radius have been used to verify that the nominal 5290.5 Angstrom wavelength of the C V I (n=8-7) multiplet is the correct wavelength for the line emitted owing to charge exchange excitation. (C) 1999 American Institute of Physics. [S0034 -6748(99)55601-3].