Three-dimensional PIC simulations of a load-limited MILO

Abstract

Summary form only given, as follows. The magnetically insulated transmission line oscillator (MILO) is a gigawatt class high power microwave (HPM) source. By relying on magnetic insulation, it permits large input powers, (10's of GW) without electrical breakdown or external magnets. Despite these advantages, magnetic insulation in conjunction with a slow wave structure results in highly non-linear RF generation, mode structure, and mode competition. While this phenomena is not generally amenable to analytic treatment, much insight can be gained from particle-in-cell (PIC) simulation. ICEPIC, a fully three-dimensional, parallel, electromagnetic PIC code developed at AFRL, allows this complex device to be simulated from end-to-end including a Vlasov antenna. By including the full geometry of the device, simulation enables the transient behavior, such as mode competition, to be studied in detail. Given the excellent agreement with experimental data, these simulations point to the importance of return current paths and antenna design in the development of unwanted non-axisymmetric modes during the start-up phase of microwave generation. The saturation and quenching of these modes and the growth of the desired operating mode are examined in detail.