Theory and design of a free-electron maser with two-dimensional feedback driven by a sheet electron beam

Abstract

The use of two-dimensional Bragg resonators of planar geometry, realizing two-dimensional (2D) distributed feedback, is considered as a method of producing spatially coherent radiation from a large sheet electron beam. The spectrum of eigenmodes is found for a 2D Bragg resonator when the sides of the resonator are open and also when they are closed. The higher selectivity of the open resonator in comparison with the closed one is shown. A time-domain analysis of the excitation of an open 2D Bragg resonator by a sheet electron beam demonstrates that a single-mode steady-state oscillation regime may be obtained for a sheet electron beam of width 100-1000 wavelengths. Nevertheless, for a free-electron maser (FEM) with a closed 2D Bragg resonator, a steady-state regime can also be realized if the beam width does not exceed 50-100 wavelengths. The parameters for a FEM with a 2D planar Bragg resonator driven by a sheet electron beam based on the U-2 accelerator (INP RAS, Novosibirsk) are estimated and the project is described.

Using 2D Distributed Feedback in Optical Laser

“…According to [3,4] the 2D Bragg resonator possesses high selectivity over both the longitudinal and the transverse indices. This selectivity originates from output of radiation not only in the longitudinal ±z directions (similar to 1D Bragg resonators), but additionally in the transverse ±x directions.…”

“…In our paper we describe an effective method for the spatial synchronization of radiation in the case of large Fresnel parameter: b 2 /lλ 1 that is based on using 2D distributed feedback. In microwave electronics 2D distributed feedback was suggested in [3,4] to produce spatially coherent radiation from either sheet or annular high-current relativistic electron beam with the transverse size greatly exceeding the wavelength and can be realised in planar and coaxial 2D Bragg cavities with a double-periodical corrugation of the metallic walls. In this structure mutual scattering of the electromagnetic energy fluxes propagating in the forward, backward and transverse directions (relative to the direction of the electron beam propagation) takes place.…”

“…For practical applications similarly to the case of metallic waveguide [4] it is sufficient to approximate sinusoidal modulation by chessboard function (see Fig. 1).…”

Effect of Ripple Taper on Coupling Modes in a Coaxial Bragg Structure

“…Taking the matched boundary conditions at both ends of the reflector, one can solve the coupled equations for each mode by using finite differential method or the eigenvector method [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Here the reflectivity for the i-th mode is defined as the ratio of the backward-wave power of the i-th mode to the forward-wave power of the operating mode at input port of the reflector.…”

Generation of Electromagnetic Fields of Extremely High Intensity by Coherent Summation of Cherenkov Superradiance Pulses

“…Approaches that can be suggested to achieve this goal include the generation of radiation by a single source with an oversized electrodynamic system. In this case special methods (for example, 2D distributed feedback [1,2]) are required to produce spatially coherent radiation. Another method is the synchronization of a large number of moderate-power sources using a master oscillator [3][4][5].…”