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

Abstract

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.