PIC simulations of power flow in a linear transformer driver for radiographic applications

The 7 cavity, 1 MV linear transformer driver for radiography at Sandia National Laboratories has recently been upgraded to 21 cavities with an output voltage of 2.5 MV. In this paper, results from 2-D, r-z particle-in-cell simulations of the full 21 cavity system are presented. Each cavity feed is driven with its own external RLC circuit that is independently triggered, and has a realistic 45° slanted vacuum/insulator. Electrons are emitted from the central cathode with a conventional space-charge-limited emission model. Detailed diagnostics monitor electron loss to the anode, cavity conductors, and the insulators. The most significant and encouraging result is that the simulations have absolutely no electron loss to the insulators, even with large random variations in the trigger timing.