Determination of plasma ion velocity distribution via charge-exchange recombination spectroscopy

Abstract

Spectroscopy of line radiation from plasma impurity ions excited by charge-exchange recombination reactions with energetic neutral beam atoms is rapidly becoming recognized as a powerful technique for measuring ion temperature, bulk plasma motion, impurity transport, and more exotic phenomena such as fast alpha particle distributions. In particular, this diagnostic offers the capability of obtaining space- and time-resolved ion temperature and toroidal plasma rotation profiles with relatively simple optical systems. Cascade-corrected excitation rate coefficients for use in both fully stripped impurity density studies and ion temperature measurements have been calculated to the principal ..delta..n = 1 transitions of He+, C/sup 5 +/, and O/sup 7 +/ with neutral beam energies of 5 to 100 keV/amu. A fiber optically coupled spectrometer system has been used on PDX to measure visible He/sup +/ radiation excited by charge exchange. Central ion temperatures up to 2.4 keV and toroidal rotation speeds up to 1.5 x 10/sup 7/ cm/s were observed in diverted discharges with P/sub INJ/ less than or equal to 3.0 MW.