Derivation of local impurity transport quantities from soft-x radiation evolution during tracer injection at W7-AS

A frequently used method for determination of impurity transport coefficien ts is the analysis of the radial and temporal time evolution of the impurit y density of injected tracer impurities. In cases when the impurity density cannot be measured directly, e.g., by active charge exchange recombination spectroscopy, the impurity density has to be reconstructed from impurity r adiation as measured, e.g., by the soft-x camera. Due to the energy integra ted information, assumption about the spatial ionization state distribution , e.g., coronal equilibrium, is necessary. This might not be valid in cases of large transport. Consequently, the transport quantities, derived under the preliminary assumption of radial coronal distribution, are used again i n an iterative way to improve the density reconstruction in order to approa ch more realistic transport quantities. The procedure was applied to plasma discharges in the stellarator Wendelstein 7-AS. (C) 1999 American Institut e of Physics. [S0034-6748(99)62301-2].