Resonance noise radiation of a non-relativistic FEL oscillator in the presence of guide magnetic field

We report electromagnetic noise radiation produced by a curvilinear electron flow with the mean electron velocities of 0.1 - 0.3 c in the Motz undulator of the period 10 mm, the amplitude of the static transversal sinusoidal undulator field 0.6 kOe and the uniform longitudinal guide magnetic field 0 - 10 kOe. The input electron beam with the diameter of 0.5 mm was created by an electron gun with a shield cathode and possessed the density of current of up to 10 A/cm/sup 2/. A resonant enhancement (by 10 - 50 times) of the spontaneous radiation was theoretically predicted and observed for first harmonics of the base frequency. The phenomenon is caused by the presence of the guide magnetic field and can be efficiently utilized in FEL devices with electron energies of up to 350 keV.