Relativistic multiwave oscillators

This report is a brief review of advances in a rapidly developing realm of science - relativistic high-frequency electronics. The term relativistic high-frequency electronics is presently used in reference to that area of vacuum electronics which harnesses electron beams with energies of 0.2-100 MeV and currents up to 10⁴ A. The resultant microwave oscillators range up to 10⁹-10¹⁰ W in power for a pulse duration of 10^-9-10^-7 s. The wavelengths utilized in this field lie in the interval from several dozen centimeters to values belonging to the visible range, i.e., span six orders of magnitude. Naturally, the family of the devices employed in these ranges is highly diversified. However, it turns out that many of them are well known in conventional microwave electronics. In this connection, of interest is the advancement of new ideas of vacuum electronics, aimed at raising the generated-or amplified-signal power and at mastering new wavelength ranges. The present report is concerned with this aspect of relativistic high-frequency electronics. It is pertinent to note that there are excellent reviews dedicated to relativistic high-frequency electronics and its application (see, for instance, Ref. [1]). Here, we endeavor to call attention to those aspects of the development of this area, which for several reasons have not been adequately discussed in the foregoing and other reviews.