Particle-in-cell Simulations of Ion Dynamics in a Pinched-beam Diode

article-in-cell simulations of a 1.6 MV, 800 kA, and 50 ns pinched-beam diode have been completed with emphasis placed on the quality of the ion beams produced. Simulations show the formation of multiple regions in the electron beam flow characterized by locally high charge and current density (“hot spots”). As ions flow through the electron-space-charge cloud, these hot spots electrostatically attract ions to produce a non-uniform ion current distribution. The length of the cavity extending beyond the anode-to-cathode gap (i.e., behind the cathode tip) influences both the number and amplitude of hot spots. A longer cavity length increases the number of hot spots yet significantly reduces the amplitude producing a smoother, more uniform ion beam than for shorter cavities. The net current and the ion bending angles are also significantly smaller with long cavities

Simulations of the generation and transport of a 5 MV end-point x-ray beam on a pulsed power generator

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