Reflex Triode X-Ray Source Research on Gamble II

Summary form only given. Reflex diode (one cathode and one anode) and triode (two cathodes and one anode) X-ray sources are investigated on Gamble II (2 MV, 2 Omega, 100 ns) to better understand the coupling of MeV-electron teams to thin converters in order to optimize emission of sub-100-keV X-rays. In conventional diodes, significant attenuation of these X-rays occurs in the converter, which is typically a large fraction (0.1 or more) of an electron-range thick. The objective of reflexing configurations is to minimize the converter thickness while maintaining good electron beam coupling. Triodes are superior X-ray sources compared with diodes in several respects, including dose production at reduced voltage and beam-coupling efficiency with reduced converter thickness. Beam dynamics are modeled using particle-in-cell (PIC) techniques, and radiation production is modeled using Monte-Carlo techniques (ITS). The modeling is in very good agreement with the experimental data, including the diode electrical behavior, the dose produced and the spectral response determined from step-wedge diagnostics. A large range of converter thicknesses were tested, from 0.1-mil gold to 10-mil tantalum. The optimum thickness for dose production is in the 0.5-to 1-mil range. The PIC modeling predicts this optimum thickness, and indicates that electron loss to large radius explains the reduction in dose for thinner converters. The coupling efficiency for these thinner converters could be improved by decreasing the triode impedance, a motivation for developing similar diodes on higher-current generators such as Saturn at Sandia National Laboratories.