N. S. Ginzburg

Common properties of free electron lasers

Abstract A general theory of microwave devices (in particular, ubitron, gyrotron) based on the ultrarelativistic Doppler up-conversion of electron oscillation frequency is developed. The wave growth rate for the amplifier and the start current for the generator are obtained. A universal relation between the frequency conversion factor and the efficiency of the laser is derived.

Nonstationary generation in free electron lasers

Abstract Evolution of the alternating field structure in the high- Q multimode cavity excited by the beam of relativistic electron oscillators is described by a self-consistent set of equations. Stationary and pulse injection regimes are investigated. The injection current increasing over the threshold, three consecutive stages take place: a) stationary single-mode generation (or, correspondingly, generation of identical pulses), b) periodic and c) stochastic self-modulation.

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.

Generation of powerful subnanosecond microwave pulses in the range of 38-150 GHz

Experimental measurements of coherent stimulated radiation from intense, subnanosecond electron bunches moving through aperiodic waveguide and interacting with a backward propagating TM/sub 0.1/ wave are presented. The ultra-short microwave pulses in Ka, W, and G band were generated with repetition frequencies of up to 25 Hz. Observation of RF breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, gives an estimate of the peak power up to 140 MW for the 300-400 ps pulses at 38 GHz. The initial observation of 75 GHz 10-15 MW radiation pulses with duration less than 150 ps, and of 150 GHz microwave spikes with a risetime of 75 ps are also reported.

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 .

Quasi-optical theory of relativistic submillimeter surface-wave oscillators

Within the framework of a quasi-optical approach, the nonlinear theory of relativistic surface-wave oscillators is developed. By presenting the radiation field as a sum of two counter-propagating wave-beams which are coupled on a shallow corrugated surface, we describe formation of an evanescent slow wave. Taking into account the excitation of a slow wave by a sheet electron beam, we simulate linear and nonlinear stages of interaction that allows us to define the threshold conditions, the electron efficiency, and the output coupling. It is shown that the considered type of an oscillator can be used for generation of powerful sub-THz radiation.