Abstract
Longitudinal space-charge forces from density fluctuations generated by shot noise can be a major source of microbunching instability in relativistic high brightness electron beams. The gain in microbunching due to this effect is broadband, extending at least up to optical frequencies, where the induced structure on the beam distribution gives rise to effects such as coherent optical transition radiation. In the high-frequency regime, theoretical and computational analyses of microbunching formation require a full three-dimensional treatment. In this paper we address the problem of space-charge induced optical microbunching formation in the high-frequency limit when transverse thermal motion due to finite emittance is included for the first time. We derive an analytical description of this process based on the beam's plasma dielectric function. We discuss the effect of transverse temperature on the angular distribution of microbunching gain and its connection to the physics of Landau damping in longitudinal plasma oscillations. Application of the theory to a relevant experimental scenario is discussed. The analytical results obtained are then compared to the predictions arising from high resolution three-dimensional molecular dynamics simulations.
Highlights
Density fluctuations due to shot noise in high brightness electron beams can couple to several impedance effects along accelerating systems, generating a broadband energy modulation
Consistent with the current theoretical and experimental understanding of the process, we model the formation of microbunching as follows: the electron beam initially undergoes an external-force-free drift and space charge generates an energy modulation starting from shot noise
In this paper we discussed a kinetic analytical description of space-charge induced optical microbunching based on the beam plasma dielectric function
Summary
Density fluctuations due to shot noise in high brightness electron beams can couple to several impedance effects along accelerating systems, generating a broadband energy modulation. We show that in the high-frequency limit, with the assumption that longitudinal motion is quasilaminar, the problem of space-charge interactions leading to microbunching growth becomes formally equivalent to that of one-dimensional plasma oscillations in a warm electron plasma The theory of such electrostatic oscillations in thermal plasmas has been discussed in two seminal papers by Landau [18] and Jackson [19]; our present work represents a new application of these venerated techniques of mathematical physics in a radically different context than the one considered in the original papers. We compare the results of our analysis and those of high resolution molecular dynamics simulations, capable of investigating spatial features in the fields below the mean interparticle distance
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