Cherenkov radiation of electromagnetic waves by electron beams in the absence of an external magnetic field

In conventional sources of coherent Cherenkov electromagnetic radiation, th e electrons move linearly, guided by external magnetic fields. In the absen ce of such fields, the electrons can move radially, being affected by the b eam self-fields as well as by the radial component of the electric field of the wave. This radial motion can, first, improve the coupling of electrons to the field of a slow wave localized near the wall of a slow-wave structu re, and second, cause an energy exchange between the electrons and the wave due to an additional transverse interaction. This interaction, in particul ar, can lead to an experimentally observed excitation of nonsymmetric trans verse electric waves in Cherenkov devices. In plasma-filled sources, the be am self-fields can be compensated for by ions, leading to a known ion focus ing of the beams. In such regimes, the beam can be surrounded by an ion lay er creating a potential well for electrons which can be displaced from stat ionary trajectories by transverse fields of the wave. The operation of such sources when the presence of ions and the radial electric field of the wav e play competing focusing and defocusing roles, and electron interception b y the walls restricts the output power level, is analyzed in stationary and nonstationary regimes.