Novel schemes of the trapping regime in the free-electron devices were studied. Proof-of-principle experiments on implementation of “non-resonant” trapping were performed in Ka-band and a high-efficiency ultra-wideband freeelectron maser-amplifier has been demonstrated. For shorter-wavelength free-electron lasers (FELs), we describe two different ways to use the regime of so-called “multi-stage” trapping: a narrow-band FEL-amplifier and a FEL operating in multi-frequency SASE regime. The advantages of the proposed regimes for increasing the FEL efficiency and for decreasing the sensitivity to the spread in parameters of the feeding electron beams are demonstrated.
A natural problem arising in the case of realization of a THz electron maser with a high-current relativistic electron beam is the use of an oversized cavity when it is difficult to provide selective excitation of a definite transverse mode. Our idea is to give up working on a fixed transverse mode, and to use excitation of a supermode formed by a fixed set of several transverse modes of an oversized waveguide. We propose to use the Talbot effect to create an oversized microwave system that provides a high Q-factor for this supermode. We present a design of a Free-Electron Maser fed by a 10 MeV / 2 kA / 200 ns electron beam and based on excitation of a Talbot-type supermode at a frequency close to 2 THz. The presentation includes results of our multi-frequency multi-mode simulations of the electron-wave interaction during the spatio-temporal process of formation and amplification of the supermode in an oversized microwave system. The calculated efficiency of this FEM at the level of 5-10% corresponds to the GW level of the output power.
Spatially-extended high-power Cherenkov masers operating in millimeter wavelength band intended for using in powering systems of Compton-type FELs are under development in collaboration of IAP RAS (Nizhny Novgorod) and BINP RAS (Novosibirsk). Electrodynamic systems of such oscillators are based on 2D periodical slow-wave structures realizing 2D distributed feedback mechanism, allowing for provision of stable narrow-band oscillation regime under conditions of substantial oversize. This novel feedback mechanism is examined for the oscillators of different geometry. Project of cylindrical slow-wave oscillator of such type operating at Ka-band with sub-GW power level was elaborated based on the tubular electron beam at the “Sinus-6” accelerator 0.5 MeV / 5 kA / 20 ns (IAP RAS). Prospect for further increase of the radiation power is studied in W-band planar Cherenkov maser driven by large-size sheet electron beam forming by the “ELMI” accelerator 1 MeV / 7 kA / 3 μs (BINP RAS). Design parameters, key components and results of simulations of these oscillators are presented, status and results of their experimental studies are discussed.
Project of high-power FEL of sub-THz to THz band is under development in collaboration of BINP RAS (Novosibirsk) and IAP RAS (N.Novgorod) based on the linac “LIU-5” 5 MeV / 2 kA / 200 ns. The aim of this project is to achieve sub-GW power level and a record pulse energy content, ~ 10 -100 J in the specified frequency bands. The design parameters and key components of the FEL are discussed. Helical pulsed undulators were elaborated allowing for effective pumping of operating bounce oscillations. New modification of Bragg structures based on the coupling of propagating and quasi-cutoff waves, so-called advanced Bragg structures, and the possibility of its use to compose the FEL electrodynamic system were studied.
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