Excitation of parasitic waves in forward-wave amplifiers with weak guiding fields.

To produce high-power coherent electromagnetic radiation at frequencies from microwaves up to terahertz, the radiation sources should have interaction circuits of large cross sections, i.e., the sources should operate in high-order modes.

Excitation of parasitic waves near cutoff in forward-wave amplifiers.

In this paper, excitation of parasitic waves near cutoff in forward-wave amplifiers is studied in a rather general form. This problem is important for developing high-power sources of coherent, phase controlled short-wavelength electromagnetic radiation because just the waves which can be excited near cutoff have low group velocities. Since the wave coupling to an electron beam is inversely proportional to the group velocity, these waves are the most dangerous parasitic waves preventing stable amplification of desired signal waves.

Mode switching in a gyrotron with azimuthally corrugated resonator.

The operation of a gyrotron having a cylindrical resonator with an azimuthally corrugated wall is analyzed. In such a device, wall corrugation cancels the degeneracy of the modes with azimuthally standing patterns. The coupling between these modes depends on the radius of electron beam.

Wave interaction in relativistic harmonic gyro-traveling-wave devices.

In gyro-traveling-wave devices, several waves can be excited at different cyclotron harmonics simultaneously. This paper analyzes the interaction between three waves synchronous with gyrating electrons at different cyclotron harmonics in two relativistic gyro-amplifier configurations; viz., gyro-traveling-wave tubes and gyrotwystrons.

Start-up scenario in gyrotrons with a nonstationary microwave-field structure.

Megawatt class gyrotrons operate in very high-order modes. Therefore, control of a gyrotron oscillator's start-up is important for excitation of the desired mode in the presence of the many undesired modes. Analysis of such scenario using the self-consistent code MAGY [M.

Self-excitation of microwave oscillations in plasma-assisted slow-wave oscillators by an electron beam with a movable focus.

Plasma-assisted slow-wave oscillators (pasotrons) operate without external magnetic fields, which makes these devices quite compact and lightweight. Beam focusing in pasotrons is provided by ions, which appear in the device due to the impact ionization of a neutral gas by beam electrons. Typically, the ionization time is on the order of the rise time of the beam current.

Overlapping of resonances and stochasticity of electron trajectories in cyclotron masers.

When an electromagnetic (EM) wave has a large amplitude and electrons have a large energy, the electron cyclotron frequency in the process of interaction with an EM wave can vary significantly. This can lead to overlapping of cyclotron resonances at different harmonics. It is shown that such an overlapping causes the stochasticity of electron orbits.

Self-consistent nonstationary processes in phase-mixed electron beams focused by mobile ions.

This paper is devoted to the analysis of nonstationary self-consistent processes in electron beam propagation in the presence of mobile ions. This problem is of particular interest for the recently developed plasma-assisted slow-wave oscillators (pasotrons). In pasotrons beam focusing is provided by ions (in contrast to other high-power microwave sources where the beam is focused by a strong external magnetic field).

Linear theory of multistage forward-wave amplifiers.

A small-signal theory describing multistage gyro-traveling-wave tubes (gyro-TWTs) is developed. Multistage configurations of gyro-TWTs as well as conventional TWTs seem to be attractive because of their principal ability to operate stably with a high gain, since the stability can be provided by a shortening of each stage while the gain increases with the number of stages. Two regimes of operation, far from cutoff and near cutoff, are considered.

Nonstationary phenomena in tapered gyro-backward-wave oscillators.

Recently, it was found that a gyro-backward-wave oscillator (gyro-BWO) with a tapered waveguide can exhibit stationary oscillations at currents which exceed the starting current by more than 2 orders of magnitude. This result, at first glance, contradicts the theory of transients in untapered linear-beam BWO's, which predicts nonstationary oscillations at currents exceeding the start current by a factor of 3. To explain this behavior of the tapered gyro-BWO, its nonstationary theory is developed.

Traveling-wave tubes and backward-wave oscillators with weak external magnetic fields.

Recent development of plasma-assisted slow-wave oscillators [Goebel et al. IEEE Trans. Plasma Sci.

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

In conventional sources of coherent Cherenkov electromagnetic radiation, the electrons move linearly, guided by external magnetic fields. In the absence of such fields, the electrons can move radially, being affected by the beam 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 structure, and second, cause an energy exchange between the electrons and the wave due to an additional transverse interaction.