Charge exchange recombination spectroscopy as a plasma diagnostic tool (invited)

Abstract

Intensity and line profile measurements of the spectra of light hydrogenic ions which are excited by charge exchange reactions with fast neutral atoms are being widely used as diagnostics for fusion plasma research. This technique, which is referred to as charge exchange recombination spectroscopy, allows measurements of the densities of fully stripped impurity ions and particle transport coefficients with only minor uncertainties arising from atomic processes. The excitation of long-wavelength transitions in light ions such as He+, C5+, and O7+ allows relatively easy measurements of ion velocity distributions to determine ion temperatures and plasma rotation velocities. Among its advantages for such measurements are the facts that fiber-optic coupling between a remote spectrometer and the immediate reactor environment is possible in many cases, the measurement is localized by the intersection region of a neutral beamline and viewing sightline, and intrinsic ions can be used so that injection of potentially perturbing impurities can be avoided. A particularly challenging application of this technique lies in the diagnosis of alpha particles expected to be produced in the present generation of Q≊1 tokamak experiments.