G.V. Sotnikov

Dielectric wake-field generator

Wake-fields excited in a dielectric media can be applied both for particles acceleration and for HF-power generation. In the present work theoretical and experimental investigations are represented on the generation of the electromagnetic wake-fields in the dielectric tube by a sequence of the relativistic electron bunches. The obtaining of the peaked high power due to the coherent superposition of the wake-fields of the regular sequence of bunches and multi-mode operation has been investigated. The measurements of wake-fields output power and the beam electron energy losses and were performed.

Microwave amplification in a coaxial slow-wave plasma transmission line

Microwave generation by an electron beam in a coaxial transmission line in which the inner and outer conductors are both corrugated is studied theoretically. An annular electron beam propagates in a transport channel filled entirely with plasma. The eigenmodes of the plasma-filled coaxial line are studied, as well as how they are affected by the plasma density. It is shown that, in the presence of a plasma, the microwaves are amplified to a significantly greater extent and the spectrum of the generated microwaves is broader. The nonlinear amplification regime is analyzed. The maximum possible amplitude of the longitudinal electric field and the interaction efficiency are determined as functions of the plasma density. A comparison between the results obtained and the analogous parameters of a vacuum structure shows that plasma-filled hybrid structures are more promising than vacuum sources.

Wakefield excitation by a relativistic electron bunch in a magnetized plasma

The excitation of a wake wave by a relativistic electron beam in an unbounded magnetized plasma and a plasma waveguide is studied theoretically. It is shown that, in a waveguide partially filled with a plasma, the energy that the electrons of the accelerated beam can gain is 37 times higher than the energy of the electrons of the beam generating wakefield.

Coaxial slowing down structure for hybrid UHF amplifier of range 1-3 GHz

The excitation by an electron beam of UHF oscillations in a coaxial slowing down transmission line with a comb on internal and external cylinders is considered. The analytical and numerical analysis of the received dispersion equation is carried out. The dependence of the gain on energy of an electron beam is investigated. It is shown, that the dependence of the gain on frequency has a maximum nearby the Cherenkov resonance of a beam with an eigen wave structure. Outside of a resonance the gain falls down under the linear law of reduction of frequency. The nonlinear theory of the UHF amplifier is constructed on the basis of the chosen slowing down structure. The maximal amplitude of a longitudinal electrical field, the efficiency of interaction and the optimum length of the structure are determined.

Effect of the ponderomotive force on the development of beam-plasma instability

The amplitude of the wave generated in a plasma during the development of beam-plasma instability is nonuniform in the longitudinal direction. The ponderomotive force associated with this nonuniformity leads to a redistribution of the plasma density; as a result, the wave amplitude and its spatial distribution change. As the beam current grows, the ponderomotive force plays an increasingly important role and radically changes the mechanism by which the beam-plasma instability saturates. Ion acoustic waves generated by the ponderomotive force propagate in the direction opposite to the propagation direction of the beam, thereby ensuring distributed feedback and giving rise to a strong low-frequency self-modulation of the wave amplitude and phase. Results are presented from experimental investigations of the self-modulation regime of the beam-plasma instability in a magnetized plasma waveguide. Theoretical estimates of the parameters of the low-frequency self-modulation agree well with the experimental data.

Effect of the microwave ponderomotive force on the development of the beam instability at different plasma and beam parameters

A study is made of the effect of the parameters of a beam and a plasma-filled waveguide in a traveling-wave tube amplifier on the stability of the amplification regime against the excitation of ion acoustic waves by the microwave ponderomotive force. It is shown that, in such an amplifier, the stability of the amplification of a microwave can be achieved by simultaneously increasing the density and energy of the electron beam.

Beam-plasma amplifier on basis of coaxial transmission line

The excitation of UHF-oscillations by an electron beam in a disk loaded coaxial transmission line with combs on the inner and external conductors are theoretically investigated. The structure passage channel, where an annular electron beam propagates, is fully filled by plasma. The eigen waves of the plasma filled coaxial transmission line and their dependencies versus plasma density are investigated. It is shown that the plasma has resulted in essentially an enhancement of gain and at the same time widens the excited oscillation spectrum.

The exciting of the wake field in the dielectric waveguide

A theoretical analysis and numerical simulation of wake-field excitation in a dielectric-lined waveguide for the generation of peaked high power emission are carried out. The theory of wake-field excitation by a single electron bunch in a dielectric-lined circular waveguide is developed, and simulation results of wake-field excitation for linear and nonlinear stages of the process are presented.

2.5-dimensional numerical simulation of relativistic electron bunch self-modulation in a plasma

This paper presents the results of 2.5-dimensional numerical simulation of both the modulation of long high-density relativistic electron bunches (REB) in a plasma and the excitation of wake fields by these bunches. The previous one-dimensional study has shown that the density profile modulation of a long bunch moving in plasma results in the growth of the wake wave amplitude. This is explained by the fact that the wake fields generated by microbunches being due to the evolution of the initially uniform bunch during the modulation, are coherent. The bunch modulation occurs at the plasma frequency. The present study is concerned with the REB motion, taking into account the plasma and REB nonlinearities. It is demonstrated that the radial REB dynamics exerts primary effect on both the REB self-modulation and the wake field excitation by the bunches formed.

Plasma nonlinearity influence on HF oscillation excitation by the electron beam in hybrid plasma waveguides

The tasks of increase of the HF power under excitation and the microwave energy extraction into the outer space are the key problems of microwave electronics. In order to solve them, the authors proposed the application of hybrid plasma waveguides. The hybrid plasma waveguide is the slow-wave structure with its passage channel filled with plasma. (HPSWS). In such a waveguide, the principal advantages of plasma electronics characteristics are realizable.