X-Ray Spectral Confirmation of Electron Reflexing in a 300-kV Reflex Triode

Summary form only given. Differential absorption spectrometers (DAS) are commonly used to measure the X-ray spectrum generated from high-current, relativistic electron beam diodes. We have previously presented a novel parametric spectral unfold technique that overcomes the problems typically observed with conventional DAS unfold approaches. In particular, the solution spectrum is independent of the choice of trial spectrum and it contains no unphysical peaks; the endpoint energy is also determined self-consistently, not a priori. In this paper we present parametric-unfold spectra obtained for a 300-kV reflex triode using the new low-energy differential absorption spectrometer (LEDAS). The LEDAS is designed for endpoints up to 500 keV, and uses ten filters with four TLDs per filter as detectors. The unfolded spectrum gave a minimized rms error of ap4% between the calculated and measured LEDAS doses. The unfolded endpoints were slightly less than, but strongly correlated with, the measured peak voltages. We also calculated two theoretical spectra for the 300-kV reflex triode using TIGERP with an input electron energy distribution calculated from the measured triode current and voltage waveforms. Boundary conditions at the converter surfaces either reflected the electrons ("reflexing") or allowed them to escape ("non-reflexing"). We then scaled the two spectra to minimize the LEDAS rms error; the errors were dominated by excess theoretical dose in the most heavily filtered (highest energy) channel. The shapes of the unfolded spectrum and the two scaled theoretical spectra showed excellent agreement below 100 keV, but the non-reflexing theoretical spectrum showed a pronounced excess at higher photon energies. The unfolded spectrum was only slightly below the theoretical reflexing spectrum near the endpoint, which might be explained by electrons losing energy in a low-Z anode plasma before striking the tantalum converter. Thus, the electrons in the 300-kV reflex triode appear to be reflexing as expected