Dimensional Bounds on Vircator Emission

Virtual cathode oscillators (vircators) are sources of short-pulsed, high-power, microwave (GHz) radiation. An essentially dimensional argument relates their radiated power, pulse energy and oscillation frequency to their driving voltage and fundamental physical constants. For a diode of width and gap 10 cm and for the voltages of a few hundred keV, the peak radiated power cannot exceed O(30 GW) and the broadband single cycle radiated energy cannot exceed O(3 J). If electrons can be accelerated to relativistic energies, higher powers and radiated energies may be possible.