Single-shot time-resolved crystal X-ray spectrometer for tokamak plasma spectroscopy

Abstract

Curved-crystal Bragg X-ray spectrometers in operation at tokamak-fusion facilities measure plasma ion temperatures by Doppler broadening of characteristic X-ray emission lines from plasma impurities and plasma rotation by Doppler shift of these lines. They can provide data on electron temperatures, densities, and coronal equilibrium comparisons. Since energy confinement times in tokamaks are of the order of 20–50 ms, it is important to make these measurements with time resolution of 20 ms or less. Heretofore to do this, data from many ‘“similar shots” had to be averaged. Each interface of the instrument reported here has been expressly optimized to provide these data on a single shot basis without averaging. Central to the design is a large area vacuum mounted crystal for reflection and focus of plasma impurity X-rays such as titanium XXI. The spectrometer has λ/Δλ wavelength resolution of > 19 000 and a relatively large wavelength focal plane while maintaining this temporal ability.