Microwave generation by a superluminal source at ultimate current densities

Summary form only given. High-power directed wideband electromagnetic (EM) radiation in the microwave range can be generated by means of a superluminal electron emission current pulse produced when the front of the electron emission from the interface between a vacuum and a medium propagates with a velocity higher than the speed of light. In particular, a superluminal current pulse is generated when a plane metal surface is irradiated by a plane flux of radiation capable of producing electron emission. According to the theory, the higher the energy of the emitted electrons, the higher the intensity and the total energy of the emitted EM radiation. Estimates show that, in order for the energy and intensity of the generated EM radiation be of interest for practical purposes, the energy of the emitted electrons should be on the order of tens of keV or higher. Under laboratory conditions, the emission current of high-energy electrons can be generated by separating processes of the electron production and the formation of the emitting dipole layer. Ionizing radiation capable of producing electron emission is used only to initiate the emission of electrons with the minimum possible energy and electrons emitted are then accelerated to their final energies by an external electric field. The results were obtained in early studies of operating modes of a radiator in which the generated electromagnetic wave did not have any significant effect on parameters of the accelerating system. However, it is clear that, for high current densities of accelerated electrons, this effect should be taken into account. When the current density is sufficiently high, characteristics of the generated EM radiation depend on parameters of the accelerated diode and, primarily, on parameters of the limiting current that can be produced above the anode. In particular, since the EM radiation pulse forms at the front of the emission current, the achievement of high current densities at the anode is determined not by the current density of the emitted electrons but by the growth rate of the emission current. Our objective is to investigate limiting characteristics of the EM radiation generated by an elementary superluminal source. We present analytical estimates and results of numerical calculations of parameters of a superluminal current pulse and EM radiation generated when the emission electrons are accelerated in a plane diode operating at high current densities.