Comparative measurement of electron density and temperature profiles in low-temperature ECR discharges by a lithium atom beam and Thomson scattering

In this paper a method to determine spatially-resolved profiles of the elec tron temperature T-e and density n(e) in an electron-cyclotron-resonance (E CR) discharge is presented. This technique is based on the observation of l ine emission from a neutral Li atom beam, which is injected into the plasma and excited by electron collisions. A collisional-radiative model valid fo r the injected Li atoms is used to predict the emission intensities as func tion of n(e) and T-e for several lines theoretically. In contrast to the el ectron temperature regime representative for the edge of tokamak discharges (T-e > 5 eV), the ECR discharge offers a T-e range where selected line int ensity ratios strongly depend on the electron temperature. Therefore, a com parison of the measured ratios with the calculated ones yields T-e profiles for the first time. The n(e) measurement is performed as in tokamaks by ob serving the attenuation of the beam due to ionization in the plasma. We pre sent radial profiles of T-e and n(e) for discharges in argon and xenon unde r different operating conditions. These results are compared with results o btained by Thomson scattering. Our measurements give evidence for a satisfy ing agreement between the two methods.