Passive Ballistic Microbunching of Non-Ultrarelativistic Electron Bunches using Electromagnetic Wakefields in Dielectric-Lined Waveguides

TL;DR

This paper demonstrates a passive technique to produce picosecond electron microbunch trains at low energy using electromagnetic wakefields in dielectric-lined waveguides, enabling applications in ultrafast science and advanced accelerators.

Contribution

It introduces and experimentally validates a passive microbunching method for non-ultrarelativistic electron beams via wakefield excitation in dielectric-lined waveguides, a novel approach in beam modulation.

Findings

Successfully generated picosecond microbunch trains at ~6 MeV.

Demonstrated preservation of density modulation during acceleration to ~20 MeV.

Validated the passive microbunching technique experimentally.

Abstract

Temporally-modulated electron beams have a wide array of applications ranging from the generation of coherently-enhanced electromagnetic radiation to the resonant excitation of electromagnetic wakefields in advanced-accelerator concepts. Likewise producing low-energy ultrashort microbunches could be useful for ultra-fast electron diffraction and new accelerator-based light-source concepts. In this Letter we propose and experimentally demonstrate a passive microbunching technique capable of forming a picosecond bunch train at $\sim 6$~MeV. The method relies on the excitation of electromagnetic wakefields as the beam propagates through a dielectric-lined waveguide. Owing to the non-ultrarelativistic nature of the beam, the induced energy modulation eventually converts into a density modulation as the beam travels in a following free-space drift. The modulated beam is further accelerated to $\sim20$~MeV while preserving the imparted density modulation.