[en] A review is given of technological advances made in the development of high-current relativistic electron accelerators which promise to revolutionize the design of high-power microwave tubes. The critical comparison in this regard, concerns the electron emission mechanism operative at the cathode of the electron gun within the tube. Conventional microwave tubes incorporate thermionic cathodes which have emissivities of at best several tens of A/cm². In contrast electron emission from the plasma-induced field emission cathodes used in high-current, pulsed accelerators is limited only by the self-forces of the electron stream acting within the diode. Under these conditions, the emitted current densities have typically ranged from 10³ to 10⁵ A/cm²