High-Power Microwave Driven Plasma Wakefield in a Cylindrical Waveguide

We present the first experimental observation of the predicted [1] high-power microwave (9.6 GHz, <500 MW, <0.5 ns) driven plasma wakefield formation in a plasma-filled cylindrical waveguide. The high-power microwave pulse is generated by a super-radiant backward wave oscillator (SR-BWO) driven by an annular electron beam (∼280 keV, ∼1.5 kA, ∼5 ns), produced by a magnetically insulated foilless diode, and guided through a slow-wave structure by a 2.5 T axial magnetic field [2]. Energetic electrons of >20 keV energy were collected in the radial direction outside the waveguide. The appearance of such high energy electrons can be related to the ponderomotive force and the plasma wakefield formation. The transmitted microwave signal shows frequency-modulation and pulse compression, the result of the plasma density modulation appearing in the wake of the propagating microwave pulse. ID analytical modeling and 3D PIC (Particle-in-Cell) simulations support the experimentally observed frequency modulation of the transmitted microwave pulse and the radial electron accelerations.