Determination of Zeff by integrating measurements from x-ray tomography and charge exchange recombination spectroscopy

The effective ionic charge, Z(eff), is determined through the integration of soft x-ray tomography and charge exchange recombination spectroscopy impurity density measurements in the Madison Symmetric Torus. Z(eff) is found is be 2.3 +/- 0.1 in the core of high temperature, high current, improved confinement discharges, with a slightly hollow profile peaking near mid-radius. A Bayesian probability framework, developed as part of an on-going effort in Integrated Data Analysis, was used to incorporate these two measurements. This framework provides a method to address different systematic and statistical uncertainties associated with each diagnostic and to test hypothetical contributions to Z(eff) against the existing data set. The combined analysis provides much higher confidence in the result than previous single-diagnostic attempts to characterize Z(eff) using near-infrared bremsstrahlung or x-ray spectroscopy.