RADIAL TEMPERATURE DISTRIBUTIONS OF C-6+ IONS IN THE TEXTOR EDGE PLASMA MEASURED WITH LITHIUM BEAM ACTIVATED CHARGE-EXCHANGE SPECTROSCOPY

A new method of obtaining the temperature of highly charged carbon ions in the boundary layer of tokamak discharges is described. Lithium beam activated charge exchange spectroscopy (Li-CXS) has been employed to measure the spectral profiles of the optical radiation following the electron transfer between impurity ions and a neutral lithium diagnostic beam. By assuming a Maxwellian velocity distribution, ion temperatures are deduced fitting a Gaussian profile to Doppler broadened charge exchange emission lines. Additional line broadening caused by magnetic fields (Zeeman effect) and collisional l-level mixing of the upper electronic state, which may both give rise to several overlapping transitions of slightly different wavelengths, is discussed. The method does not depend on the presence of neutral injection heating beams and is therefore useful for investigating various heating situations, such as Ohmic discharges, beam heated plasmas and high frequency heated plasmas, as well as combinations thereof. The paper presents measurements of ohmically heated and beam heated discharges and discusses their implications with regard to the determination of the plasma D+ temperature and the amount of carbon removed from limiter surfaces owing to C6+ --> C self-sputtering.