Beam-Driven Transverse Deflecting Structure for Femtosecond Electron-Beam Diagnostics

TL;DR

This paper introduces a beam-driven transverse deflecting structure that uses wakefields to achieve femtosecond-scale electron-beam diagnostics with lower power requirements than traditional RF-based methods.

Contribution

It proposes a novel beam-driven TDS design utilizing wakefields in a resonant cavity array for high-resolution, low-power electron-beam diagnostics at multi-GeV energies.

Findings

Simulations show ~1.6 fs temporal resolution at 14 GeV.

The structure scales toward sub-femtosecond resolution at higher charge.

Demonstrates feasibility for high-energy, high-resolution beam diagnostics.

Abstract

High-resolution longitudinal phase-space (LPS) diagnostics are essential for X-ray free-electron lasers and advanced accelerators. Conventional radio-frequency transverse deflecting structures (TDSs) provide direct femtosecond-scale LPS measurements, but their substantial RF-power and infrastructure requirements strongly limit their deployment at multi-GeV beam energies. Here, we propose a beam-driven transverse deflecting structure in which a leading driver bunch, separated by one RF bucket from a trailing witness bunch under study, excites long-lived wakefields in a resonant cavity array. By placing the witness bunch near a zero crossing of the wakefield, the bunch experiences an approximately linear time-dependent transverse kick. Electromagnetic simulations of the resonant structure, combined with start-to-end beam-dynamics simulations based on European XFEL parameters at a final beam energy of 14 GeV, demonstrate a temporal resolution of $\sim 1.6$ fs for a 500 pC driver bunch, with a clear scaling toward the sub-femtosecond regime at higher charge.