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An experimental campaign was recently completed at the U.S. Naval Research Laboratory’s Mercury pulsed-power facility, where the feasibility of using a 5 MV inductive voltage adder (IVA) as a pulsed photoneutron source was studied. In these experiments, a large-area bremsstrahlung diode was fielded on the Mercury accelerator, producing an intense, pulsed x-ray beam, which generated photoneutrons when striking an appropriate target. This paper reports on simulations that were performed to study the production of the electron beam in the diode, and the generation and transport of the x-ray beam. Comparison is made between the numerically predicted beam properties and results obtained during the experimental campaign. Various models of electron and ion emission from the electrodes in the generator were simulated, and the effect of model parameter choices on the dose predictions is described.

Recent experiments on the Mercury pulsed power accelerator were performed with a large-area bremsstrahlung diode operated at 5 MV. Extensive measurements of the x-ray dose distribution were made using TLDs, both in the near field and far field of the x-ray beam. In order to understand the operation of the diode and the properties of the x-ray beam, numerical simulations of the diode and beam were performed. Particle-in-cell simulations of the diode were driven using the measured currents from the experiment in order to simulate the electron beam produced by the accelerator. These beam electrons were then used as a source in Monte Carlo simulations of the bremsstrahlung converter to compute the generated x-ray beam. The photons from this simulation were then transported to the near- and far-field TLD locations and doses were computed. The dose predictions were compared to measurements, showing reasonably good agreement.