Multichordal spectroscopy on JT‐60

In order to study impurity behavior on the JT‐60 plasma, a spectroscopic diagnostic system, which is capable of measuring many spectra of impurity ions and their spatial distributions simultaneously, has been developed. This system consists of interchangeable unit‐type spectrographs which have different lines of sight. Four types of grazing incidence spectrographs are prepared as unit‐type spectrographs. These spectrographs cover the nominal wavelength regions 0.5–5, 0.5–50, 2.0–50, and 50–122 nm, respectively, and have holographic gratings with flat focal fields. Image‐intensified 1024‐ or 512‐channel photodiode arrays are used as detectors for all spectrographs. Four unit‐type spectrographs are used for observing the main plasma, and two unit‐type spectrographs are used for observing the plasma near the null point of the diverted discharge. One of these spectrographs has been calibrated absolutely in the wavelength region 27.5–120 nm using synchrotron radiation from the Photon Factory (National Laborato...