Temperature profiles of C6+-ions in the TEXTOR edge plasma - measured with lithium-beam activated charge-exchange spectroscopy

We employ a new method to obtain the temperatures of highly charged carbon ions in the boundary layer of tokamak discharges. The lithium-beam activated charge-exchange spectroscopy ('Li-CXS') is used to measure spectral profiles of lines in the visible region excited by electron transfer between impurity ions and a fast neutral lithium diagnostic beam. Assuming a Maxwell velocity distribution of the ions, temperatures are deduced by fitting a Gaussian profile to the Doppler broadened emission lines. Additional non-thermal line broadening due to magnetic fields (Zeeman-effect) and due to a collisional l-level-mixing of the upper electronic state, which may both give rise to several overlapping transitions of slightly different wavelengths, has been taken into account. The method does not depend on the presence of NI-heating beams and therefore is capable of investigating different heating scenarios, including ohmic discharges, beam-heated and high-frequency-heated plasmas, as well as combinations thereof. Furthermore, the relatively high cross-section of charge-exchange between neutral lithium and carbon ions allows the use of a narrow beam diameter and a low current density, so that strictly local measurements of ion temperatures can be performed without changing plasma conditions by the diagnostic experiment itself. In this paper, we present radial temperature profiles of the fully stripped C6+, which have been obtained with and without additional NI-beam-heating in the outmost 20 cm of TEXTOR plasmas, for the first time using the neutral lithium diagnostic beam. (author) 9 refs., 2 figs