Aachen PK 2003 – wissenschaftliches Programm
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P: Plasmaphysik
P 10: Poster II
P 10.21: Poster
Dienstag, 18. März 2003, 17:30–19:15, Foyer
Reconstruction of edge Zeff profiles from bremsstrahlung data via (semi-)Blind Source Separation methods on TEXTOR — •Geert Verdoolaege, Giuseppe Telesca, and Guido Van Oost — Department of Applied Physics, Ghent University, Rozier 44, 9000 Gent, Belgium
The understanding of the behaviour of impurities is a critical issue in tokamak physics. At the tokamak TEXTOR we run a diagnostic for determining the effective ion charge Zeff from bremsstrahlung measurements in the visible.
However, a major problem in determining a Zeff profile is posed by the incertitude at the plasma edge on the different contributions to the measured continuum signal, as well as by the routine use of estimated edge values for Te and ne. As a result, the interpretation of a profile is rendered problematic outside the central plasma. In fact, so far none of the available methods for the determination of Zeff has been able to extend the Zeff profile up to the edge, which is at present a real challenge.
Now, a measured line-integrated emissivity signal can be considered as a linear or nonlinear function of a number of signals from which Zeff can be derived directly. Several methods for (semi-)Blind Signal Separation (BSS) allow the separation of signal mixtures into their components, (mainly) based on the statistical properties of each contribution. We have conducted a preliminary experiment with multi-channel linear Independent Component Analysis, which indeed already suggests that certain features in the data can be attributed to the evolution of a well-defined physical parameter, in this case Zeff.