ELECTRON BUNCHING IN THE CLINOTRON-TYPE OSCILLATORS. “CLINOTRON” AS A FREQUENCY MULTIPLIER

There is a problem of designing convenient in use and not particularly expensive oscillators for mastering the sub-millimetre waveband. The backward wave oscillators (BWOs) provide good results in the long-wavelength part of the sub-millimetre waveband. However, their advancement in the short-wavelength part of the sub-millimetre waveband causes substantial problems. Existing technological opportunities do not allow to obtain extremely thin high-current-density electron beams necessary for this waveband. Application of the frequency multipliers could weaken requirements to the electron beams considerably. A clinotron-type oscillator can be used for bunching electron beam in the frequency multiplier. In the clinotron oscillator, a wide and comparatively thick sheet electron beam is directed at a small angle to the surface of the slow-wave structure and is partly dispersed on this surface. Clinotron provides output powers a few orders of magnitude greater than conventional BWOs of the same waveband. This is important for obtaining good (i.e., deep) bunching of an electron beam. In clinotron-type oscillators, it is necessary to investigate the process of dense electron bunching and to clarify the conditions of its use for bunching electron beam in a frequency multiplier. In this article, numerical simulation of electron bunching is conducted in the clinotron by means of our previously in-house designed special computer program, which takes into account the specifics of the clinontron operational regime. Three-dimensional motion of electron is investigated in the finite focusing (guide) magnetic field. As a result of numeral simulations, we find the effect of “layer-by-layer” bunching of the electron beam in a clinotron-type oscillators. The farther an electron layer is located from the surface of the slow-wave structure the later electron bunching in that layer occurs.  We show that singling out the clinotron operating regime and the slope angle of the guide magnetic field to the surface of the comb allows one to ensure the formation of dense electron bunches in the part of the beam outside the clinotron slow-wave structure, where the second slow-wave structure (working in the power-catching regime) must be located. Thus, the principal possibility of the clinotron use for designing a frequency multiplier is proved.