Spectral dynamics of mm-wave radiation from two-channel planar FEM with two dimensional distributed feedback

Abstract

The paper presents the experimental results on generation of high power 4-mm radiation in a two-channel planar free electron maser (FEM) with two-dimensional distributed feedback. The experiments are carried out at the ELMI-device. The FEM oscillator consists of two channels driven by two relativistic electron sheet beams (1 MeV/1 kA/5 µs). Each channel contains a hybrid two mirror resonator composed of two-dimensional upstream and one-dimensional downstream Bragg reflectors with transverse sizes exceeding the radiation wavelength by one order of magnitude. This two-dimensional distributed feedback circuit provides a well reproducible single-mode mm-wave generation regime. In our experiments with this two-channel FEM oscillator, radiation at 75 GHz with a spectrum width of ∼20 MHz in pulses with ∼200 ns duration and ∼50 MW power was obtained1. The present paper describes the recent experimental results on generation of different single longitudinal modes with frequencies close to the resonator eigenmodes by varying the parameters of the electron beams and the undulator magnetic field. The temporal dynamics of the radiation spectra has been measured and will be discussed.