Single-Shot Characterization of High Transformer Ratio Wakefields in Nonlinear Plasma Acceleration

TL;DR

This paper demonstrates a single-shot method to characterize high transformer ratio wakefields in nonlinear plasma acceleration using energy-modulated witness beams and spectral analysis, enabling detailed wakefield profiling and drive beam reconstruction.

Contribution

It introduces a novel single-shot spectral measurement technique for high transformer ratio PWFA, validated by simulations, and demonstrates direct observation of beam-loaded transformer ratios up to 7.8.

Findings

Achieved transformer ratios up to 7.8 in nonlinear PWFA.

Developed a spectral reconstruction method for drive beam profiles.

Validated the technique with 3D particle-in-cell simulations.

Abstract

Plasma wakefields can enable very high accelerating gradients for frontier high energy particle accelerators, in excess of 10 GeV/m. To overcome limits on total acceleration achievable, specially shaped drive beams can be used in both linear and nonlinear plasma wakefield accelerators (PWFA), to increase the transformer ratio, implying that the drive beam deceleration is minimized relative to acceleration obtained in the wake. In this Letter, we report the results of a nonlinear PWFA, high transformer ratio experiment using high-charge, longitudinally asymmetric drive beams in a plasma cell. An emittance exchange process is used to generate variable drive current profiles, in conjunction with a long (multiple plasma wavelength) witness beam. The witness beam is energy-modulated by the wakefield, yielding a response that contains detailed spectral information in a single-shot measurement. Using these methods, we generate a variety of beam profiles and characterize the wakefields, directly observing beam-loaded transformer ratios up to R=7.8. Furthermore, a spectrally-based reconstruction technique, validated by 3D particle-in-cell simulations, is introduced to obtain the drive beam current profile from the decelerating wake data.