Multichannel grazing-incidence spectrometer for plasma impurity diagnosis: SPRED

A compact vacuum ultraviolet spectrometer system has been developed to provide time-resolved impurity spectra from tokamak plasmas. Two interchangeable aberration-corrected toroidal diffraction gratings with flat focal fields provide simultaneous coverage over the ranges lO0-1100 Å or 160-1700 Å. The detector is an intensified self-scanning photodiode array. Spectral resolution is 2 Å with the higher dispersion grating. Minimum readout time for a full spectrum is 20 msec, but up to seven individual spectral lines can be measured with a 1-msec time resolution. The sensitivity of the system is comparable with that of a conventional grazing-incidence monochromator.