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The determination of Z(eff) from visible continuum radiation is based on the assumption that the line-integrated continuum signal is mostly composed of Bremsstrahlung radiation. In practice a wavelength window relatively free of spectral lines is selected, and the line-integrated continuum signal along different chords from the edge up to the central plasma is measured. The local emissivity epsilon(r) is then calculated using an Abel inversion procedure, and the Z(eff) profile can be obtained. Although theory and techniques are well established, in any experimental device there remains an uncertainty in the calculated value of Z(eff) due to the non-Bremsstrahlung radiation from the cooler edge plasma. As a consequence, the local Bremsstrahlung emissivity in the outer region of the plasma cannot be determined and the signal measured along every chord through the plasma contains a spurious contribution. In this paper the error in the value of the central plasma emissivity and Z(eff) due to edge radiation has been investigated. Qualitative analytical considerations have been complemented by a qualitative analysis, consisting of the comparisons of test emissivity profiles with Abel-inverted profiles obtained from the integrals along central chords only. The Z(eff) diagnostic on TEXTOR with the data evaluation procedure is described, as is the limiter configuration.

Additional information

Authors: TELESCA G, Ecole Royale Militaire, Bruxelles (BE);VAN OOST G, Ecole Royale Militaire, Bruxelles (BE);ONGENA J, Ecole Royale Militaire, Bruxelles (BE);LEYS C, Ecole Royale Militaire, Bruxelles (BE);SCHOON N, Universiteit Gent, Laboratorium voor Natuurkunde (BE)
Bibliographic Reference: Article: Proceedings of the 19th Conference on Controlled Fusion and Plasma Physics, Vol. 2 (1992) pp. 1147-1150
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