Development of compact multi-channel ultra soft X-ray spectrometer for high-accuracy particle transport measurement

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Impurity transport coefficients can be evaluated with a high degree of accuracy by using a combination of a tracer-encapsulated solid pellet (TESPEL) and a charge exchange recombination spectroscopy (CXS). The goal of this research project is the development of a compact multi-channel ultra soft X-ray (USXR) spectrometer, which is necessary for the CXS diagnostic with a high-energy neutral beam. We adopted the optical system that consists of a grid collimator and a multilayer mirror, for achieving the compactness together with the high throughput. We produced a prototype one-channel USXR spectrometer with the above optical system. During the experiment on the Large Helical Device (LHD), a working gas for LHD plasmas flowed accidentally into the prototype USXR spectrometer, and then MCP detectors with being applied a high voltage was damaged. To fix this problem, the design Of the spectrometer is modified and we proceed with the installation of differential pumping system with a cryopump. Unfortunately, since the countermeasure work takes a longer time than anticipated, we cannot obtain the experimental data from the modified spectrometer. However, we made progress in the research using existing spectrometers for studying USXR emissions from the tracer impurity ions introduced by the TESPEL injection. Several calculation codes, which are necessary secondarily for the calculation of the impurity transport coefficients using an impurity transport code, have been developed. Although the development of the multi-channel USXR spectrometer remains to be done, it can be easily done by aligning the optical system adopted here in a fan shape, owing to the compactness of that.