Spontaneous superradiant sub-THz coherent cyclotron emission from a short dense electron bunch

Short dense electron bunches produced by modem photoinjectors are attractive from the viewpoint of the realization of powerful and effective sources of subterahertz radiation based on the spontaneous coherent mechanism of emission. This type of emission is realized if the effective phase size of the bunch with respect to the radiated wave is small enough. Therefore, the repulsion of particles caused by a strong Coulomb field inside the dense electron bunch strictly limits the duration of the radiation process due to the increase in the bunch length. We show that this problem can be solved by using the cyclotron mechanism of the spontaneous radiation due to the effect of compensation of the Coulomb repulsion in the phase space.