Consistency check of Z(eff) measurements in ergodic divertor plasmas on Tore Supra

On Tore Supra, the mean effective charge Z(eff) of the plasma is deduced ro utinely from line integrated measurements of visible Bremsstrahlung. In ord er to get a deeper understanding of this measurement, and to obtain high co nfidence in the data, we have compared the visible Bremsstrahlung data to l ine radiation of impurities present in the plasma, removing any error from the processing technique. The paper presents a systematic study of the corr elation between the Z(eff) derived from the two methods, and the dependence on plasma parameters and geometrical factors. A good correlation is found, independent of the position of the outboard pump limiter (OPL). However, t he fitting parameter of the empirical method is different for different pla sma currents, due to the variation of the emission profiles. The agreement between the two methods is good, confirming the role of carbon and oxygen a s the main impurities in the Tore Supra tokamak. (C) 2001 Elsevier Science B.V. All rights reserved.