High Resolution X-Ray Spectroscopy Diagnostics of High Temperature Plasmas

Abstract

This paper presents advances in the use of high resolution x-ray spectroscopy for the measurements of tokamak plasmas and the study of atomic processes. The measurements refer to H- and He- like spectra of Ar (λ = 3.7 to 4.2 Å) obtained with a new crystal spectrometer at the Alcator C tokamak. With record count rates of up to 0.5 MHz, time resolved spectroscopy of individual plasma discharge was demonstrated at the 20 ms time scale. In particular, the time evolution of ion and electron temperatures, Ti(t) and Te(t), was determined and occurrences of transient plasma phenomena were recorded in discharges with deuterium pellet injection. X-ray line emission was for the first time observed along different chords through the plasma so as to determine the radial dependence of the principal plasma parameters Ti(r) and Te(r). These radial scan data are shown to be of interest for identifying manifestations of underlying atomic processes and ion transport effects. On the basis of the present results we assess the future use of x-ray spectroscopy diagnostics to obtain extended information on the temporal and spatial dependences of the main plasma parameters together with new information on transient phenomena as well as on the neutral content of tokamak plasmas.