The medium-power millimeter-wave sources are widely used in radars, space telecommunications, and spectroscopy. For microwave generation with power level from tens of watts to several kilowatts, slow-wave devices such as traveling-wave tubes (TWTs) and backward-wave oscillators (BWOs) are widely used. Traditionally, these radiation sources are based on utilizing thin rectilinear electron beams guided through thin cylindrical channel in slow-wave structures of helical, folded-waveguide, or coupled-cavity types. For millimeter or shorter wavelengths, a very thin electron beam with very high energy density is needed, which hinders the guiding of the beam in a proximity of the slow-wave structure wall, especially in CW regime. In order to mitigate the described difficulty, a new concept of medium-power slow-wave devices of the millimeter-wavelength range is proposed.1 This concept is based on the usage of azimuthally-symmetric or helically corrugated operating waveguides and hollow rectilinear thin-wall electron beams instead of pencil-like beams. It should be noticed, that slow-wave devices with relativistic hollow electron beams are widely used.2 In the weakly-relativistic case, the exploit of hollow beams permits a significant increase in the diameter of the beam channel and, simultaneously, a drastic decrease in the required current density and heat load at the interaction structure wall in comparison with the conventional devices with pencil-like beams.
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