Photon-counting CCD detector as a tool of x-ray imaging

A new x-ray imaging technique to measure magnetic axis and two-dimensional soft x-ray energy spectra for a long-pulse discharge has been developed by utilizing a soft x-ray photon-counting charge-coupled-device (CCD) camera. This system consists of pinholes, Be filters, and a 1024×1024 frame-transfer back-illumination CCD detector (the imaging area has 1024×512 pixels). By choosing appropriate combinations of pinholes and Be filters, the x-ray flux is adjusted to the level suited for photon-counting mode and imaging mode, respectively. The Shafranov shift is derived from a two-dimensional soft x-ray intensity map measured in the imaging mode in the compact helical system (CHS) and large helical device. Two-dimensional profiles of electron temperature and two-dimensional profiles of high-Z impurity Kα radiation intensity are derived from two-dimensional energy spectra of x rays measured in photon-counting mode for the CHS hot-electron-mode plasma.