Super-radiance in a prebunched beam free electron maser

It is well known that electrons passing through a magnetic undulator emit p artially coherent radiation: "Undulator Synchrotron Radiation". Radiation f rom electrons, entering the undulator at random, adds incoherently. If the electron beam is periodically modulated (bunched) to pulses shorter than th e radiation wavelength, electrons radiate in phase with each other, resulti ng in super-radiant emission at the bunching frequency. Introduction of a s ignal at the input of the prebunched beam FEL, results in stimulated super- radiant emission. The interaction between the electromagnetic wave and a sy nchronous modulated e-beam results in amplification of the signal wave in a ddition to the spontaneous super-radiant emission. We demonstrated and meas ured the super-radiant emission in a wide band of frequencies from 3.15 to 5.5 GHz using the mini-FEM of Tel-Aviv University, wherein pre-bunching at the radiation frequency is accomplished with the aid of a traveling-wave pr ebuncher. The measured upper synchronous frequency is centered about 4.5 GH z and the lower synchronous frequency is just above cutoff (near 3.153 GHz) . Analytical models, computer simulations and experimental results of a pre -bunched free-electron laser operation are presented and compared. The powe r levels that can be achieved are discussed. The measured results agree wel l with results predicted theoretically and obtained by a 3D simulation code . (C) 2000 Published by Elsevier Science B.V. All rights reserved.