Alexey V. Palitsin

Waveguide resonators with combined Bragg reflectors

We present a method to improve the selective properties of a waveguide resonator with Bragg reflectors on both ends, a passive device that is widely used in microwave engineering and optoelectronics. It is shown that additional mode conversions lead to a significantly rarefied spectrum of eigenoscillations with different transverse field structures. In particular, this can be achieved by using doubly periodic Bragg reflectors with different azimuthal symmetries forming four wave resonant field structures. The analysis of dispersion properties presented is applicable for resonators of arbitrary relation of lengths of the reflectors and waveguide.

Self-consistent theory of cyclotron phenomena in a relativistic BWO

We have developed a self-consistent theory for a relativistic backward wave oscillator (BWO) taking into account the interaction of fast cyclotron waves of the electron beam with both the operating contrary wave and the forward wave. The theory describes the extraction of electromagnetic energy from the interaction space, providing a correct description of the operation of a relativistic BWO in which the field structure is a product of the self- consistent solution. The theory suggests ways in which the requirement of a guide magnetic field in such devices can be reduced.

Suppression of parasitic self-excitation in Cherenkov amplifiers

A means for removing the parasitic feedback in microwave amplifiers, the main obstacle to achieving a high gain, is described here. The method is based on utilizing the resonant interaction between fast cyclotron waves on an electron beam and the electromagnetic waves that are propagating in the opposite direction. This is an effective method to prevent detrimental self-excitation in amplifiers whose operation is based upon the stimulated Cherenkov radiation of a forward-propagating electron beam in a guiding magnetic field. Conditions for the resonant interaction are provided by proper choice of the guiding magnetic field. At such resonances the counter-propagating waves are in stop-bands and, therefore, cannot propagate. Results of theoretical and experimental investigations of cyclotron absorption of counter-propagating waves in amplifiers are given in the present work. It is shown that the resonant cyclotron interaction leads to a complete suppression of the feedback and that the threshold of self- excitation becomes unachievable even for large reflections. Only a minor decrease in the amplification results in comparison with an ideal amplifier without reflections. It follows from these results that a spatially varying magnetic field can be applied along the axis of the amplifier to expand the zone of the cyclotron absorption and thereby exclude a re-tuning of the self-excitation frequency.

Measurement of high-power microwave pulses by resistive hot-electron sensors

Use of hot-electron semiconductor detectors for the measurement of high-power microwave pulses may lead to anomalously large errors. Methods of separation of the error signal and determination of the measurement error are considered.

Low-impedance relativistic backward wave oscillator

It is shown that the limiting electron-beam current in a relativistic backward wave oscillator (BWO) can be increased using a slow-wave system (SWS) in the form of a circular waveguide with shallow rectangular corrugation. This idea was checked both experimentally and numerically for a 3-cm BWO with a short homogeneously corrugated SWS and a resonance reflector-modulator. The experiments showed that the proposed BWO with an explosion-emission electron gun and said SWS can effectively operate on 60-Ohm electron beams at a gigawatt output power.

Cyclotron suppression of pre- and post-pulse radiation from a relativistic BWO pulse

The possibility of using cyclotron interaction to suppress pre- and post-pulse radiation from a relativistic BWO is considered. It is shown that resonant cyclotron absorption, which depends on electron energy, is as able to suppress unacceptable generation as to eliminate reflected signals.

Dynamics of transient processes in relativistic backward wave tube driven with an external electromagnetic signal

The paper is devoted to theoretical and experimental study of relativistic backward wave tube driven with input electromagnetic signal. It was observed that input electromagnetic signal of “traditional” electronic devices can produce essential effect on operation of relativistic backward-wave tube despite its low level compared with the power of relativistic electron beam. It can reduce start-up time or even by impact for auto-oscillations in hard regime. There are parameter regions where frequency control can be realized: amplification and phase locking.

Relativistic backward-wave tube with a smooth control over output radiation pulse duration

The effect of failure of oscillations in a low-impedance backward-wave tube is described and the possibility of using this effect for controlling the duration of output radiation pulses is considered.

Nonlinear Stationary Waves in Thin-Walled Electron Beams

Summary form only given. We analyze conditions under which a double-humped potential function of electron beam states is formed in a system of coordinates that is moving with the electrons. We show that periodic states with large amplitudes can exist. Such states can be used as the basis for microwave oscillators with a strong Doppler frequency shift. In addition, we predict the existence of solitary waves in thin-walled electron beams. The dependence of the velocity of such solitons on their amplitudes is obtained. Equations for various states of sheet electron beams, including states with two-dimensional solitons, are also presented.

On Bursian and Pierce Instabilities of Electron Beams Propagating in Weakly Irregular Channels

Summary form only given. The stability of stationary states of dense electron beams propagating in weakly irregular channels, in particular, in channels with non-deep periodically corrugated walls, is investigated using the method of coupled waves. We show that Bursians instability can develop, leading to the formation of virtual cathodes or their disruption. In unlimited channels, separate zones of absolute and convective instabilities on the omega-k plane (Brillouins diagram) are possible. In a channel of finite length, these zones are merged forming the well-known Bursians instability in a vacuum channel or Pierces instability when a space charge of electrons is neutralized by immobile ions. In addition, we investigate the influences of limited conductivity of channel walls, joined elements and other irregularities.