Wall reflection modeling for charge exchange recombination spectroscopy (CXRS) measurements on Textor and ITER

TitleWall reflection modeling for charge exchange recombination spectroscopy (CXRS) measurements on Textor and ITER
Publication TypeJournal Article
Year of Publication2010
AuthorsS. Banerjee, P. Vasu, M. von Hellermann, R.JE Jaspers
JournalPlasma Physics and Controlled Fusion
Volume52
Number12
Pagination14
Date PublishedDec
Type of ArticleArticle
ISBN Number0741-3335
Accession NumberISI:000284406600056
KeywordsCONCEPTUAL DESIGN, NEUTRAL BEAM, SPECTRA, SURFACES
Abstract

Contamination of optical signals by reflections from the tokamak vessel wall is a matter of great concern. For machines such as ITER and future reactors, where the vessel wall will be predominantly metallic, this is potentially a risk factor for quantitative optical emission spectroscopy. This is, in particular, the case when bremsstrahlung continuum radiation from the bulk plasma is used as a common reference light source for the cross-calibration of visible spectroscopy. In this paper the reflected contribution to the continuum level in Textor and ITER has been estimated for the detection channels meant for charge exchange recombination spectroscopy (CXRS). A model assuming diffuse reflection has been developed for the bremsstrahlung which is a much extended source. Based on this model, it is shown that in the case of ITER upper port 3, a wall with a moderate reflectivity of 20% leads to the wall reflected fraction being as high as 55-60% of the weak signals in the edge channels. In contrast, a complete bidirectional reflectance distribution function (BRDF) based model has been developed in order to estimate the reflections from more localized sources like the charge exchange (CX) emission from a neutral beam in tokamaks. The largest signal contamination of similar to 15% is seen in the core CX channels, where the true CX signal level is much lower than that in the edge channels. Similar values are obtained for Textor also. These results indicate that the contributions from wall reflections may be large enough to significantly distort the overall spectral features of CX data, warranting an analysis at different wavelengths.

URL<Go to ISI>://000284406600056
Division

Fusion Physics

PID

1a055fccfdf4f1f8795c6a238fd3389f

Alternate TitlePlasma Phys. Control. Fusion

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