High-Efficiency Single-Mode Free-Electron Maser Oscillator Based on a Bragg Resonator with Step of Phase of Corrugation

Abstract

A new type of high-selective Bragg resonator having a step of corrugation inside the interaction region was used as a microwave system for a free-electron maser (FEM). Using a LINAC LIU-3000 (1 MeV/200 A/200 ns) to drive the FEM oscillator, a single-mode single-frequency operation was achieved at a frequency of 30.74 GHz with an output power of about 50 MW, which corresponded to a record efficiency of 35% for a millimeter wavelength FEM.

Comparitive Study of Coaxial Bragg Resonators

“…As many authors pointed out, the Bragg resonators with a step of corrugation phase always causes a narrow pass band in the stop bands, which can be controlled by selecting the Bragg reflector parameters [26][27][28][29][30][31][32][33]. This phenomenon corresponds to the sharp dip appearing in the stop bands in Figs.…”

“…If the regular waveguide section between the two reflectors is absent, the Bragg resonator is simplified to consist of only two Bragg reflectors, where connection of these two reflectors is smooth with corrugation-phase difference Δ=0, or is step-changed with phase difference Δ = +π or −π, respectively. In previous literatures the latter was refereed to as a Bragg resonator with a localized defect, or with a step of corrugation phase [26][27][28][29][30][31][32][33]. As was demonstrated by the experiment in Ref.…”

“…As was demonstrated by the experiment in Ref. [28], a cylindrical Bragg resonator with a step of corrugation phase at the point of connection of the two reflectors has an attractive peculiarity: it possesses only one eigenmode inside the zone of effective Bragg reflection with very high Q factor, which allows the free-electron oscillator to operate in single mode with short cavity length.…”

“…Previous studies on the Bragg resonators with a step of corrugation phase were mainly concentrated on planar or cylindrical structures [26][27][28][29][30][31]. Up to date, even though very few literatures have been devoted to the coaxial Bragg resonator with a step of corrugation phase, only transmission was discussed within the restriction that the operating mode was TEM mode [32], or that both the upstream and downstream reflectors have equal length [33].…”

Bandwidth Study of the Microwave Reflectors with Rectangular Corrugations

“…A strong resonance Bragg cavity can be produced by two such axial periodic structures. A narrow band free electron laser (FEL) using the Bragg resonator was experimentally demonstrated in Ka-band and proved the advantages of high output power and high interaction efficiency [14,15].…”