N. Yu. Peskov

EXPERIMENTAL OBSERVATION OF SUPERRADIANCE IN MILLIMETER-WAVE BAND

Abstract The first experimental results of the observation of superradiance from a single subnanosecond electron bunch are presented. Superradiance was associated with different varieties of stimulated emission (bremstruhlung, cyclotron, Cherenkov, etc). Unique megawatt power level microwave pulses of short duration (0.3–0.5 ns) have been obtained.

Two-dimensional double-periodic Bragg resonators for free electron lasers

Abstract To realize spatial coherent radiation of ribbon relativistic electron beams with the transverse dimension essentially exceeding the wavelength, we propose the use of a two-dimensional distributed feedback. This feedback can be provided in a Bragg resonator formed by two double-periodic corrugating metal plates, when additional transverse electromagnetic energy fluxes, that synchronize the radiation of individual parts of the electron beam, take place. Eigenmodes of the 2D Bragg resonator are found and its high selectivity is proved.

The use of a hybrid resonator consisting of one-dimensional and two-dimensional Bragg reflectors for generation of spatially coherent radiation in a coaxial free-electron laser

The use of a novel hybrid scheme of a two-mirror Bragg resonator consisting of one-dimensional (1D) and two-dimensional (2D) reflectors is suggested for generation of powerful spatially coherent radiation in a coaxial free-electron laser driven by a large-size (102–103 wavelengths) high-current annular relativistic electron beam. The 2D Bragg reflector is positioned at the cathode side of the oscillator to provide synchronization of radiation from the oversized electron beam via transverse energy fluxes, which arise due to scattering on the 2D Bragg structure. The conventional 1D Bragg reflector is positioned at the collector side to complete the feedback.

Theory of free-electron maser with two-dimensional distributed feedback driven by an annular electron beam

The use of two-dimensional (2D) distributed feedback is considered as a method of providing spatially coherent radiation from an oversized annular electron beam. To realize the feedback mechanism, 2D Bragg structures formed from doubly-corrugated waveguide sections of coaxial geometry are suggested. The properties of two types of coaxial cavities formed using such structures are compared: a single-section 2D Bragg cavity and a two-mirror cavity. The eigenmodes of both cavities are found and their high selectivity over both azimuthal and longitudinal indices was demonstrated. Time-domain analyses of the excitation of the cavities by an annular electron beam were carried out. The influence of the cavity parameters on the oscillation regime is analyzed and discussed. It was shown that for a specific set of 2D Bragg cavity parameters it is possible to obtain a regime of steady-state oscillations when the transverse size of the beam exceeds the wavelength by a few orders of magnitude, while outside this parame...

Experimental studies of two-dimensional coaxial Bragg structures for a high-power free-electron maser

The experimental studies of two-dimensional (2D) coaxial Bragg structures are presented. These structures, which realize 2D distributed feedback, have been recently proposed as a method of producing gigawatt power level spatially coherent radiation from a free-electron maser driven by a large-size relativistic electron beam of annular geometry. The experimentally obtained frequency dependence of transmission coefficients for the 2D Bragg structures are in good agreement with theoretical predictions that demonstrates the operation of the two-dimensional Bragg scattering mechanism.

Dynamics of free-electron lasers with two-dimensional distributed feedback

Abstract Using the time domain analysis we studied the processes of oscillations build-up and spatial synchronization in FELs with two-dimensional distributed feedback driven by a large size sheet and tubular relativistic electron beams. It is proved that proposed feedback mechanism allows to ensure powerful spatial-coherent radiation when the ratio between transverse size of the electron beam and wavelength runs up to 10 2 –10 3 .

Mode competition and control in free electron lasers with one- and two-dimensional Bragg resonators

We present a time domain analysis of the longitudinal and azimuthal mode dynamics which occur in relativistic free electron lasers and cyclotron autoresonance masers with one-dimensional (1-D) and two-dimensional (2-D) Bragg resonators. It is shown that when the 1-D oscillator is moderately above threshold, a single longitudinal mode generation regime is established due to nonlinear mode competition. The process of longitudinal mode selection is more effective if the region of synchronous interaction between the electron beam and the forward propagating wave is extended inside the Bragg reflectors. Further above the oscillation threshold, multimode chaotic behavior occurs. In the second part of this paper, it is shown that both traditional 1-D and novel 2-D Bragg resonators can produce radiation at a single frequency with a one-mode azimuthal distribution which corresponds to spatial synchronization of the electromagnetic radiation. In 1-D systems, electronic mode selection occurs via nonlinear mode competition. In contrast, electrodynamic mode selection occurs in 2-D Bragg resonators, resulting in the production of a single azimuthally symmetric mode after the linear stage of evolution. The 2-D Bragg resonator is shown to retain its selectivity when its radius greatly exceeds the radiation wavelength.

Tunable terahertz band planar Bragg reflectors

A tunable planar narrow-band Bragg reflector based on coupling of the two propagating modes and a cutoff mode is considered. Coupled-wave analysis together with direct numerical simulations demonstrate operation of the proposed scheme up to the terahertz frequency band. Compatibility with the transportation of an intense electron beam encourages the use of a novel Bragg reflector in powerful long-pulse free electron lasers.

Generation of spatially coherent radiation in free-electron masers with two-dimensional distributed feedback

The results of theoretical and experimental studies on the generation of spatially coherent electromagnetic radiation in a planar free-electron maser with two-dimensional distributed feedback are reported. A two-dimensional Bragg structure is used at the initial part of the interaction space to ensure the transverse synchronization of the radiation. The possibility of the narrowband generation in the 75-GHz frequency band is demonstrated experimentally for a sheet kiloampere electron beam whose width is 20 times larger than the wavelength.

Experimental observation of wiggler superradiance under group synchronism condition

Abstract The first results of the observation of superradiance from a single, subnanosecond, high current, electron bunch passing through a wiggler immersed in a guide magnetic field are presented. The 300–500 ps microwave pulses were generated in the high gain regime for both the conventional and reverse directions of the guide magnetic field. The dependence of the radiation power on the interaction length as well as the absolute value of the power, 100–200 kW, were related with the development of self-bunching and consequently with coherent emission.