HIGH RESOLUTION X-RAY SPECTROSCOPY AT JET

Abstract
A high resolution X-ray crystal spectrometer was installed at JET in 1986. The main task of this instrument, designed and built by the ENEA Frascati Laboratory in collaboration with JET, is the measurement of the ion temperature and rotation velocity from Doppler broadenings and shifts. Stringent operation requirements considerably conditioned its versatility as a survey instrument or a tool for fundamental research. The unique conditions of the JET plasmas, however, allowed to observe in high resolution and identify lines from the highest ionization stages (B-like to H-like) of nickel in the vicinity of the resonance transitions of the one- and two-electron systems of this element. These spectra and their relevance to the study of JET physics are briefly presented. The comparison with atomic physics theoretical computations of He-like and H-like ions spectra observed at JET is also shortly presented. The most intense among these lines could regularly be monitored with adequate time resolution as to allow the production of an extensive data base. The experimental spectra are simulated by integrating the theoretical ones along the spectrograph line of sight across the plasma. Ion temperature as well as rotation velocity measurements in ohmic plasmas and additionally heated ones are discussed and their relationship with other physical quantities and operational parameters are shortly reviewed. Details of the spectrometer design, its lay-out on the JET site and its operational capabilities are also given.