High throughput ultrasoft x-ray polychromator for embedded impurity pellet injection studies

Abstract

A prototype ultrasoft x-ray polychromator has been developed for local particle transport measurements in magnetic fusion devices using the Hα charge exchange emission from low-Z impurity pellets. High throughput together with few cm radial resolution in the plasma are achieved using a toroidally aligned grid collimator, while a few Å spectral bandpass together with strong background rejection are obtained using planar multilayer mirrors and foil filters. As high sensitivity detectors we use a new type of compact, efficient and high-gain multichannel plates. The prototype instrument has been evaluated in the laboratory and tested on the Large Helical Device in Japan. In addition to transport studies, this type of device is of interest for next step experiments, where high beam energy and strong attenuation will make visible charge exchange recombination spectroscopy difficult.