The Interaction of a High-Power Sub-Nanosecond Microwave Pulse With Plasma

We present the results of experiments, analytical modeling, and numerical particle-in-cell (PIC) simulations for the propagation of a high-power, sub-nanosecond microwave pulse through a plasma-filled cylindrical waveguide in a parameter regime not studied before. Depending on the experimental conditions, the non-linear interaction of the high-power microwave (HPM) pulse with the plasma results in self-channeling through it or causes the formation of a wakefield. To study this phenomenon, two backward wave oscillators (BWOs), operating in the super-radiant mode at frequencies of 9.6 and 28.6 GHz, were designed and tested. These BWOs were driven by an electron beam (~280 keV, ~1.5 kA, ~5 ns) generated in a magnetically insulated foil-less diode, from which it propagates through a slow wave structure guided by an external axial magnetic field. Microwave pulses of ~0.4-ns width, up to ~500-MW peak power at 9.6 GHz, and up to ~1.2 GW at 28.6 GHz were obtained. These powerful subnanosecond timescale microwave beam pulses were injected into the neutral gas, plasma, or their mixture in various configurations.