Tungsten spectroscopy for the measurement of W-fluxes from plasma facing components

Abstract

Tungsten is foreseen for a full W-divertor of JET where tungsten will totally replace carbon as the material for the target plate. Also ITER operation is planned to be carried out with tungsten as one of the first wall materials, e.g. in the upper regions of the lower divertor. For the characterization of the accompanying plasma surface interaction a thorough spectroscopic diagnostic of the W influx into the plasma is of utmost importance. In order to upgrade the experimental and theoretical spectroscopic data beyond the present use of the W I transition (5d56s7 S3–5d56p7P4) at 4008 Å, an extension to lines of other (preferably longer) wavelengths has experimentally been carried out and accompanied by calculations. The survey resulted in an assessment of four additional lines in the longer (4294.61, 4886.90, 4982.59 and 5053.28 Å) and two in the shorter wavelength range (2551.35 and 2681.42 Å). The lines emitted from tungsten particles which were released by the plasma from tungsten plates and limiters in the TEXTOR edge plasma were observed with different (also high resolution) spectrometers and the Zeeman pattern was studied in order to identify possible influences of nearby interfering plasma spectral lines. The effect of the ground state level population as well as cascading from higher levels is included in the calculation of the relative line intensities and of the respective S/XB-values, the conversion factor for photon into particle fluxes. Measured and calculated S/XB-values for the 4008 Å line agrees well whereas some of the other lines are probably strongly affected by not yet identified factors.