Construction, calibration, and application of a compact spectrophotometer for EUV (300-2500-Å) plasma diagnostics

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Abstract
A 400-mm normal incidence concave grating spectrophotometer, specifically designed for plasma diagnostics, is described. The wavelength drive, in which the grating is translated as well as rotated, is discussed in detail; the wavelength linearity of the sine drive and methods of improving it are analyzed. The instrument can be used in any orientation, is portable under vacuum, and quite rugged. The construction techniques utilized produce a high quality vacuum making the instrument compatible with both high purity plasma devices and synchrotron radiation sources. The photometric sensitivity calibration was found to be very stable during extended use on high temperature plasma devices. The applications of the instrument to diagnose plasmas in two tokamaks and a mirror device are described. A facility used for photometric calibration of extreme ultraviolet (λ > 300-Å) spectrophotometers against NBS standard diodes is described. The instrumental calibration obtained using this facility was checked by using synchrotron radiation from SURF II; very good agreement was observed.