High‐power coherent microwave generation from oscillating virtual cathodes

The formation of an oscillating virtual cathode by a relativistic electron beam and the subsequent generation of coherent microwaves are investigated. If the electron beam is of high quality, the microwaves excited in a cylindrical waveguide are found to occupy a very narrow band (Δω/ω∼5%) primarily in a single transverse magnetic mode. Furthermore, the efficiency of microwave production is demonstrated in our computer simulations to be as high as 20%. It is also shown quantitatively that the efficiency decreases monotonically as the mean scattering angle of the electron beam increases.