Five-chord high-resolution x-ray spectrometer for Alcator C-Mod

A five-spectrometer array has been designed to provide high-wavelength resolution x-ray spectra from the Alcator C-Mod plasma. Each independently scannable von Hamos type spectrometer consists of a variable entrance slit, quartz crystal, and position sensitive proportional counter, and has 3 cm spatial resolution with a resolving power of 4000. The wavelength range of each spectrometer is from 2.8 to 4.0 A, which covers the complete Rydberg series of helium- and hydrogen-like argon. Wavelengths are remotely selectable, with 120 mA covered at any one setting. The array will provide single shot ion temperature profiles by measuring the Doppler broadening of the resonance lines of argon. Five proportional counters have been fabricated and all five spectrometers have been constructed. Calibration spectra using cadmium and scandium anode sources have been obtained, and measured performance characteristics are presented