High-resolution duo-multichannel soft x-ray spectrometer for tokamak plasma diagnostics

A high-resolution, time-resolving soft x-ray multichannel spectrometer (SOXMOS) that permits the simultaneous measurement of emission in two different spectral ranges has been developed and tested extensively for tokamak plasma diagnostics. The basic instrument is a high-resolution, interferometrically adjusted, extreme grazing incidence Schwob-Fraenkel duochromator. The instrument is equipped with two multichannel detectors that are adjusted interferometrically and scan along the Rowland circle. Each consists of an MgF₂ coated, funneled microchannel plate, associated with a phosphor screen image intensifier that is coupled to a 1024-element photodiode array by a flexible fiber-optic conduit. The total wavelength coverage of the instrument is 5-340 Å with a measured resolution (FWHM) of about 0.2 Å when equipped with a 600-g/mm grating, and 5-85 Å with a resolution of about 0.06 Å using a 2400-g/mm grating. The simultaneous spectral coverage of each detector varies from 15 Å at the short wavelength limit to 70 Å at the long wavelength limit with the lower dispersion grating. The minimum readout time for a full spectral portion is 16 ms, but several individual lines can be measured with 1-ms time resolution by selected pixel readout. Higher time resolution can be achieved by replacing one multichannel detector with a single channel electron multiplier detector. Examples of data from the PLT and TFTR tokamaks are presented to illustrate the instrument's versatility, high spectral resolution, and high signal-to-noise ratio even in the 10-Å region.