Formation of Compressed Flat Electron Beams with High Transverse-Emittance Ratios

TL;DR

This paper demonstrates the production and optimization of compressed flat electron beams with high transverse-emittance ratios using numerical simulations, aiming to enhance applications in advanced light sources and accelerators.

Contribution

It introduces optimized flat-beam transformation techniques for beams with fractional energy spread, validated through start-to-end simulations at Fermilab's ASTA facility.

Findings

Achieved flat beams with emittance ratios up to 400.

Produced high peak currents up to 5.5 kA.

Validated parameters suitable for wakefield excitation and photon flux generation.

Abstract

Flat beams -- beams with asymmetric transverse emittances -- have important applications in novel light-source concepts, advanced-acceleration schemes and could possibly alleviate the need for damping rings in lepton colliders. Over the last decade, a flat-beam-generation technique based on the conversion of an angular-momentum-dominated beam was proposed and experimentally tested. In this paper we explore the production of compressed flat beams. We especially investigate and optimize the flat-beam transformation for beams with substantial fractional energy spread. We use as a simulation example the photoinjector of the Fermilab's Advanced Superconducting Test Accelerator (ASTA). The optimizations of the flat beam generation and compression at ASTA were done via start-to-end numerical simulations for bunch charges of 3.2 nC, 1.0 nC and 20 pC at ~37 MeV. The optimized emittances of flat beams with different bunch charges were found to be 0.25 {\mu}m (emittance ratio is ~400), 0.13 {\mu}m, 15 nm before compression, and 0.41 {\mu}m, 0.20 {\mu}m, 16 nm after full compression, respectively with peak currents as high as 5.5 kA for a 3.2-nC flat beam. These parameters are consistent with requirements needed to excite wakefields in asymmetric dielectric-lined waveguides or produce significant photon flux using small-gap micro-undulators.