A WIDE WAVELENGTH RANGE SPECTROMETER (1150-8000 A) FOR THE RFX REVERSED FIELD PINCH EXPERIMENT

This paper describes the vacuum Czerny-Turner spectrometer with a 1.33 m focal length installed on the RFX fusion experiment. The optics are coated with MgF2 and the image intensifier, protected by a vacuum sealed MgF2 Window, features a dual photocathode system, CsTe on one half and S20 on the other; thus the instrument covers efficiently the wide spectral range from the MgF2 limit to the near infrared. Sensitivity at short wavelengths is limited by the reflectance of mirrors and the transmittance of the MgF2 window. The detector is completed by a fast optical multichannel analyzer whose 1024 photodiodes can be read out in a time of 250 mus. The instrument can also be operated in a duochromator mode by deflecting the diffracted beam onto a second detector system, where two photomultipliers are applied to two exit slits, one fixed and the other remotely movable in such a way that the intensity ratios of two lines can be monitored for diagnostic purposes. Some examples of obtained spectra illustrating the instrument performance and comprising first results from the RFX plasma are presented.