Enhancement of Free-Electron Maser Radiation by Prebunching of the E-beam (Stimulated Super-radiance)

(WE-2-04) Presenting Author: Meir Arbel

M. Arbel, A. L. Eichenbaum, H. Kleinman, I. M. Yakover, Y. Pinhasi, A. Abramovich, M. Tecimer, Y. Luria, A. Gover  

Tel-Aviv University

An electron beam (e-beam) prebunched at a synchronous FEM frequency and traversing through a waveguide, coaxial with a magnetic undulator, emits coherent radiation at the bunching frequency. Introduction of a radio-frequency (r.f.) signal at the input of the waveguide in addition to the premodulated e-beam leads to more efficient interaction, and more power can be extracted from the electron beam. In order to achieve this, the density modulation of the electron beam should be in proper phase in respect to the r.f. signal.

We report a first experimental demonstration of the stimulated super-radiance effect (amplified prebunched beam FEL radiation). Our experimental setup allowed control of the density modulation index of the electron beam, the r.f. input power level, and the phase between the r.f. input and the modulation of the e-beam. We investigated experimentally the influence of the phase difference between the modulation of the e-beam and the r.f. signal, and of the amplitudes of each, on the interaction process and the radiation power.

A comparison between the measured radiation power levels, for various phase correlation conditions and various density modulation and r.f. signal levels, with those predicted by theory and by simulation was made and is discussed.