Iron Kα measurement of LHD plasmas using a wide band and compact x-ray crystal spectrometer

X-ray spectra of FeKα transitions have been obtained on the Large Helical Device (LHD) using a wide band and compact x-ray spectrometer. The spectrometer consists of a Johann-type LiF(220) crystal with a curvature of 430mm and a back-illuminated charge-coupled device (CCD) detector with a size of 26.6×6.7mm2. A wide energy range of 6.4–7.0keV can be observed with high brightness and high temporal resolution, which enables us the measurement of Kα transitions from all charge states of Fe ions. An energy resolution of the spectrometer was 10eV at full width at half maximum. Time-developed Kα spectra after injection of Fe-coated impurity pellet were also measured with a time interval of 10ms in the full binning mode of CCD in order to analyze the impurity transport at the central column of LHD plasmas. The system can be modified to have better time response up to 1ms to analyze the ionization and recombination processes after the pellet injection.