Vacuum Ultraviolet Spectroscopy at TEXTOR

Abstract

Spectroscopy in fusion experiments is an important tool to identify impurities in the plasma and to analyze their properties based on the measurement of their characteristic line radiation. For the temperature range typical in fusion plasmas, the dominant part of each impurity in the plasma is highly ionized, and its most intense spectral lines radiate in the vacuum ultraviolet (VUV) wavelength range (10 to 200 nm). The VUV overview spectrometers installed at TEXTOR working at moderate resolution allow one to identify intrinsic plasma impurities such as B (Z = 5), C (Z = 6), Fe (Z = 26), and Cu (Z = 29) as well as seeded impurities such as Ne (Z = 10) and Ar (Z = 18) and to derive information on their relative densities in the plasma. Optimizing these spectrometers for high time resolution provides a tool to analyze transient phenomena like impurity transport processes. In combination with impurity transport modeling and atomic data, the radial distribution of the radial diffusion coefficient is determined from the experimental data. For the case of ohmic discharges, the effective radial diffusion coefficient is found to be anomalously enhanced by more than one order of magnitude as compared to neoclassical predictions.