Spontaneous coherent radiation of stabilized dense electron bunches

Modern electron sources allow formation of dense bunches with energies of 3–6 MeV, ps pulse durations, and charges of up to 1 nC. Such bunches can be used for the realization of relatively simple terahertz sources based on spontaneous coherent radiation. This regime is realized when the effective bunch phase size doesn’t exceed 2p. Power and duration of the process of such type of emission are limited due to an increase in the bunch length under the Coulomb repulsion. This complicates the effective implementation of the regime of spontaneous coherent radiation for dense bunches. Therefore, special methods for stabilization of the length of the bunch should be used. We describe several methods of the stabilization used in different systems (cyclotron radiation, emission in the traditional undulator system, and emission in the “negative-mass” undulator system).