A. M. Malkin

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.

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.

Powerful surface-wave oscillators with two-dimensional periodic structures

We propose planar relativistic surface-wave oscillators with two-dimensional periodic gratings. Additional transverse propagating waves emerging on these gratings synchronize the emission from the wide sheet rectilinear electron beam which allows realizing a Cherenkov millimeter wave oscillator with gigawatt output power.

Oversized co-axial and cylindrical surface-wave oscillators with two-dimensional periodical grating (quasi-optical model)

Within the quasi-optical approach, we study nonlinear dynamics of co-axial and cylindrical surface-wave oscillators with two-dimensional periodic gratings. Electromagnetic fields in these structures are formed by a superposition of coupled quasi-optical wave-beams propagating in the azimuthal and longitudinal directions. Presence of the azimuthal wave-beams leads to a substantial spectrum rarefication of the modes with different azimuthal indices thus allowing their selective excitation by a large radius rectilinear hollow electron beam.

Quasi-optical model of relativistic surface-wave generators for millimeter and submillimeter range

A nonlinear, nonstationary theory of relativistic surface-wave generators for the microwave range has been constructed in the framework of a quasi-optical approach. The radiation field is represented by two counter-propagating quasi-optical waves that are coupled at a corrugated surface so as to form an evanescent wave mode. A synchronous interaction with a straight sheet electron beam takes place with allowance for the surface wave retardation. An experimentally implemented prototype of the relativistic surface-wave generator operating in the millimeter range has been simulated and it shown that generators of this type can be developed so as to operate in the submillimeter range.

Cherenkov masers with two-dimensional distributed feedback

The possibility of using a two-dimensional (2D) distributed feedback to generate spatially coherent radiation by straight sheet and annular electron beams is studied. The schemes of sectional Cherenkov masers with the transverse synchronization of radiation performed in a 2D Bragg structure, which is arranged at the cathode end of the interaction space and conjugates the longitudinal and transverse (azimuthal) wave flows, is analyzed. By introducing dissipation into this structure, it is possible to increase the transverse dimensions of masers to a level on the order of 103 wavelengths with the corresponding increase in the total output radiation power without changing spectral characteristics and decreasing the energy conversion efficiency.

Terahertz free-electron lasers with bragg structures based on the coupling between traveling and quasicritical waves

The possibility of creating high-power tunable planar terahertz free-electron lasers based on modified Bragg structures with the coupling of paraxial and transverse (with respect to the velocity of particles) wave fluxes has been demonstrated. In addition to the compatibility with the transport channels of intense electron beams, the advantage of the proposed structures is the spatial coherence of radiation at a large oversize factor of the interaction region in two transverse coordinates.

Relativistic surface-wave generators based on two-dimensional periodic structures

In order to increase the integral output radiation power of relativistic surface-wave generators, it is suggested to use two-dimensional (2D) periodic slow-wave systems. Numerical simulations of dynamics of a new variant of these generators showed that additional wave beams, which appear in the 2D structure and propagate in the transverse direction, are capable of synchronizing radiation from a wide sheet electron beam. This circumstance makes it possible to implement surface-wave generators operating in the millimeter wavelength range at a gigawatt power level—e.g., based on the ELMI high-current accelerator at the Institute of Nuclear Physics (Novosibirsk).

Improvement of Stability of High Cyclotron Harmonic Operation in the Double-Beam THz Gyrotrons

A double-beam scheme of a short-wavelength gyrotron operating at the second cyclotron harmonic is studied both within the framework of the averaged self-consistent approach and using 3-D particle in cell simulations. The analysis shows that the introduction of an additional generating electron beam allows drastically increasing the operating current of a second-harmonic gyrotron with the simultaneous suppression of self-excitation of spurious modes at the fundamental harmonic. As a result, the radiated power of a double-beam gyrotron exceeds the power of a single-beam gyrotron by a factor of four. The developed concept makes it possible to realize high-power (several hundred watts) single-mode gyrotrons in the 0.7-1.0-THz frequency range.

Quasi-optical theory of radiation amplification by electron flow above resistive metal surface

Linear and nonlinear stages of a dissipative instability that arises in an electron flow above a resistive metal surface, have been studied in the framework of a quasi-optical approach with the Leontovich impedance boundary conditions. It is shown that this instability can be used for the amplification of short-wavelength radiation including that in the terahertz frequency range.