Beam emission spectroscopy on thermal helium is used at the TEXTOR tokamak as a reliable method to obtain radial profiles of electron temperature T e (r, t) and electron density n e (r, t). In this paper the experimental realization of this method at TEXTOR and the status of the atomic physics employed as well as the major factors for the measurement's accuracy are evaluated. On the experimental side, the hardware specifications are described and the impact of the beam atoms on the local plasma parameters is shown to be negligible. On the modeling side the collisional-radiative model (CRM) applied to infer n e and T e from the measured He line intensities is evaluated. The role of proton and deuteron collisions and of charge exchange processes is studied with a new CRM and the impact of these so far neglected processes appears to be of minor importance. Direct comparison to Thomson scattering and fast triple probe data showed that for high densities n e > 3.5 × 10 19 m −3 the T e values deduced with the established CRM are too low. However, the new atomic data set implemented in the new CRM leads in general to higher T e values. This allows us to specify the range of reliable application of BES on thermal helium to a range of 2.0 × 10 18 < n e < 2.0 × 10 19 m −3 and 10 eV < T e < 250 eV which can be extended by routine application of the new CRM.
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 (5d 5 6s 7 S 3 -5d 5 6p 7 P 4 ) 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.
Rate coefficients for the excitation and ionization of neutral as well as singly ionized particles and-predominantly-their ratios S(D)/XB, which are important for the conversion of photon into particle fluxes in ionizing fusion boundary plasma, have been modelled and experimentally determined in boundary plasmas for fusion-relevant species such as He
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