Abstract
The use of both spatial premodulation and negative mass instability is promising for the energy enhancement and spectrum narrowing of the undulator radiation from dense electron bunches formed in modern laser-driven photoinjectors. Combining these two methods will permit the formation of long-lived trains of short and dense bunches with very large charges, which are able to efficiently emit a much more powerful and narrow-band terahertz radiation than single bunches with the same total charge, or premodulated bunches in the positive mass oscillation regime. The development of radiation instability in the negative mass regime can enable significant quasiperiodic self-modulation of relatively long nonmodulated bunches resulting in their fairly efficient and selective terahertz superradiance.
Highlights
1Ariel University, Ariel 2Institute of Applied Physics, Russian Academy of Sciences, 603950 Nizhny Novgorod, Russia (Received 2 May 2018; published 5 October 2018). The use of both spatial premodulation and negative mass instability is promising for the energy enhancement and spectrum narrowing of the undulator radiation from dense electron bunches formed in modern laser-driven photoinjectors
Short electron bunches with a moderately relativistic electron energy of 3 to 6 MeV and a charge of the order of 1 nC, which can be formed in laser-driven photo injectors [1,2,3], are attractive for the generation of coherent spontaneous terahertz radiation [4,5,6,7,8,9,10,11,12,13,14]
The particles move for a long time in a strong field of the radiated electromagnetic pulse and are bunched by the combination wave formed by the undulator field and the radiated wave as in free-electron lasers
Summary
Short electron bunches with a moderately relativistic electron energy of 3 to 6 MeV and a charge of the order of 1 nC, which can be formed in laser-driven photo injectors [1,2,3], are attractive for the generation of coherent spontaneous terahertz radiation [4,5,6,7,8,9,10,11,12,13,14]. The modulation is assumed to allow the use of much longer electron bunches with larger charges, and a significant enhancement of energy and narrowing of the radiation spectra as well It was shown in [15] that the Coulomb repulsion of particles from areas with increased density in thin premodulated bunches leads to changes in the initial density modulation and excitation of plasma waves. The “flickering” behavior of such disappearance and reappearance of modulation corresponds to a similar character of coherent radiation that can be generated by the modulated bunches in undulators or other radiation devices Another character of the evolution of relatively long modulated bunches and their radiation should be expected when the particles are not repulsed from areas with increased density, but are attracted to them.
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