Abstract
Plasma-based accelerators (PBAs), having demonstrated the production of GeV electron beams in only centimetre scales, offer a path towards a new generation of highly compact and cost-effective particle accelerators. However, achieving the required beam quality, particularly on the energy spread for applications such as free-electron lasers, remains a challenge. Here we investigate fundamental sources of energy spread and bunch length in PBAs which arise from the betatron motion of beam electrons. We present an analytical theory, validated against particle-in-cell simulations, which accurately describes these phenomena. Significant impact on the beam quality is predicted for certain configurations, explaining previously observed limitations on the achievable bunch length and energy spread. Guidelines for mitigating these contributions towards high-quality beams are deduced.
Highlights
Plasma-based accelerators (PBAs), having demonstrated the production of GeV electron beams in only centimetre scales, offer a path towards a new generation of highly compact and cost-effective particle accelerators
Having reached GeV energies in only centimeter scales[4,5,6,7,8], femtosecond-long electron bunches with kiloampere current[9,10] and micron-level emittance[11,12], PBAs are becoming increasingly attractive for applications such as free-electron lasers (FELs)[13] or future linear colliders[14], which would strongly benefit from reduced size and cost
We show that the transverse oscillations of beam electrons, induced by the strong focusing fields in the plasma wake, can be a significant source of uncorrelated energy spread as well as increased bunch length due to path length differences between particles with different oscillation amplitude
Summary
Plasma-based accelerators (PBAs), having demonstrated the production of GeV electron beams in only centimetre scales, offer a path towards a new generation of highly compact and cost-effective particle accelerators. We show that the transverse oscillations of beam electrons (known as betatron motion), induced by the strong focusing fields in the plasma wake, can be a significant source of uncorrelated (or slice) energy spread as well as increased bunch length due to path length differences between particles with different oscillation amplitude These effects were already known[41,42], no model exists to date for their impact on the beam parameters. We present here a novel analytical theory, validated against numerical simulations with the particle-in-cell (PIC) codes OSIRIS43 and HiPACE44, which accurately describes these phenomena in the assumption of relativistic electrons in a non-evolving wake This model allows us to understand previously observed limitations, such as a finite energy spread even when the initial bunch www.nature.com/scientificreports length approaches zero[45], and define guidelines for minimizing the impact of these phenomena for high-quality electron beams
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