The knowledge of the effective ion charge Zeff which indicates the degree of plasma pollution is of high interest, since the tolerable impurity concentration to achieve successful ignition of a fusion plasma is limited. The quantification of Zeff at ASDEX Upgrade has been carried out by means of Integrated Data Analysis in the framework of Bayesian probability theory which allows the combined analysis of different bremsstrahlung and charge exchange diagnostics to obtain one joint Zeff profile. With this tool it is possible to assess the quality of the data acquired by the individual diagnostics and to find a reasonable selection of data for the routine Zeff analysis. The Zeff results are validated by the examination of different discharge scenarios and successfully applied to simulations of the neutron rate and the loop voltage. The investigation of Zeff for nitrogen seeded discharges reveals a correlation between the confinement improvement and the increase in Zeff.
Determination of Zeff by integrating measurements from x-ray tomography and charge exchange recombination spectroscopy