Abstract
Short dense electron bunches produced by modern 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.
Highlights
Modern sources of dense electron beams allow the formation of compact and accessible sources of dense electron bunches with a moderate energy of 3–6 MeV, picosecond pulse durations, and charges of up to 1 nC and even greater [1,2,3,4,5,6]
We have developed the theory of electron cyclotron masers to the situation when a short dense electron bunch produces spontaneous radiation of a short wave packet
In devices with axial character of the electron bunching in the field of the radiated wave (FELs and Cherenkov devices), this problem should be solved by means of providing either a mechanism of compensation of the Coulomb repulsion or a mechanism of axial compression of the bunch inside the radiation region
Summary
Modern sources of dense electron beams (including laser-driven photoinjectors) allow the formation of compact and accessible sources of dense electron bunches with a moderate energy of 3–6 MeV, picosecond pulse durations, and charges of up to 1 nC and even greater [1,2,3,4,5,6]. If the “operating” radiation mechanism of the sub-THz source is based on the longitudinal electron bunching [15] (free-electron lasers and Cherenkov masers), axial expansion of the bunch leads automatically to an increase in the bunch phase size with respect to the radiated wave This results in the saturation of the process of spontaneous emission. This accumulation leads to the formation of a powerful short wave pulse propagating together with the bunch It was shown [21,25,26] that this superradiant regime provides the maximal growth rate of the cyclotron instability in the case of the traditional induced character of the emission (when the bunch is much longer than the wavelength). V, we discuss some peculiarities of the regime of the spontaneous coherent superradiant emission
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