Development of the Ultrasoft X-Ray Diagnostic for Impurity Transport Studies with a Tracer-Encapsulated Solid Pellet Injection on LHD

A prototype ultrasoft X-ray polychromator for impurity transport studies using a tracer-encapsulated solid pellet (TESPEL) has been recently developed at Johns Hopkins University and tested on the Large Helical Device. The system has high throughput with good spatial (a few cm) and spectral (0.1˜0.2 nm) resolution and millisecond time response for measuring faint charge-exchange recombination emissions from the fully stripped low-Z tracer impurity. The signals from the magnesium tracer deposited locally by TESPEL injection have been successfully obtained with the prototype polychromator.