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Specific features of mode spectrum of planar structures with two-dimensional Bragg corrugation (theory and “cold” experiment)

“…Correspondingly, the use of this approximation is expedient for analyzing the generation processes upon excitation of such cavities by electron flows. The main results of such an analysis are presented in [22] and demonstrate that the use of 2D Bragg cavities allows one to obtain spatially coherent radiation in FEMs for transverse sizes l x /λ ≤ 10 2 -10 3 of a system (i.e., practically unbounded on the scale of the existing electron flows). On the basis of the performed studies, 2D Bragg cavities were designed, which are used to ensure mode selection in a planar FEM oscillator at a working frequency of 75 GHz, being developed jointly by BINP SB RAS and IAP RAS with the use of ELMI accelerator (BINP SB RAS).…”

“…Within the framework of the geometrical-optics approximation, mutual scattering of partial waves by an "ideal" 2D Bragg lattice can be described by equations of coupled waves for slowly varying amplitudes A + (x, z), A − (x, z) and B + (x, z), B − (x, z) [4,17]:…”

“…Note, however, that the "ideal" sinusoidal shape of the 2D corrugation, considered in the basic theoretical papers [3,4,17], is very difficult to realize in practice. For this reason, structures with simpler corrugation having the form of mutually perpendicular rectangular grooves (Fig.…”

“…Their transverse sizes and power can reach 140 cm and 10-100 GW, respectively [1,2]. To obtain spatially coherent radiation of such beams, it was suggested to use the twodimensional (2D) distributed feedback [3,4] which can be realized in Bragg cavities with 2D-periodic wall corrugation (2D Bragg cavities). First experiments demonstrating feasibility of planar FEM with twodimensional distributed feedback were performed on the basis of a high-current ELMI accelerator (BINP SB RAS) [5,6].…”

Diffraction selection of modes in planar backward-wave oscillators

“…For the generators based on interaction with traveling waves and the case of beams having transverse sizes which exceed the wavelength considerably, a most effective solution to this problem is the use of two-dimensional distributed feedback produced by two-dimensional Bragg structures [1,2]. The energy flows formed in these structures are transverse to the direction of translational motion of particles and synchronize the radiation of individual parts of the electron flow, which has a sheet or tubular configuration.…”