X-treme diagnostics for HID lamps?

X-ray induced fluorescence has been used to measure elemental number densities of all constituents in a ceramic metal-halide discharge lamp. High-energy synchrotron radiation generated at the Sector I Insertion Device beam line at the Advanced Photon Source induced K-shell fluorescence in the high-pressure arc plasma. High signal-to-noise fluorescence spectra of Hg, Dy, Cs and I could be simultaneously obtained. A method for absolute calibration enabled us to map density distributions of all constituents throughout the whole lamp with a spatial resolution of 1 mm(3). Elemental ratios show clear evidence of radial de-mixing of metal additives. A possible explanation for the on-axis depletion is ambipolar transport of positive ions out of the center of the arc. The highly successful experiments demonstrate the utility of modern x-ray sources and methods for diagnostics as new tools for improved understanding of high-pressure arc discharges.