Superradiotive instability during electron bunch motion in ondulator in ondulator field or electromagnetic wave pumping field

An instability is considered of the superradiative type, which is realized in motion of an electron bunch of a finite length in the ondulator field or in electromagnetic wave pumping field. A thresholdless character of the instability is shown and its increments are determined. In result of instability development takes place bunch particle bunching and coherent radiation of particles at frequencies, near to frequencies of individual radiation (scattering) of particles. At translational bunch velocity, near to the velocity of light, the frequency of HF radiation component (in the direction of translational motion) may substantially exceed the particle oscillation frequency