Femtosecond probing of light-speed plasma wakefields by using a relativistic electron bunch

TL;DR

This paper demonstrates a femtosecond-resolution technique using a relativistic electron bunch to probe and visualize the electric field structure of light-speed plasma wakefields, advancing plasma accelerator diagnostics.

Contribution

It introduces a novel method for mapping the electric fields of plasma wakefields with femtosecond precision using a high-energy electron probe.

Findings

Reconstructed wakefield from density-modulated probe bunch

Visualized linear wakefields in low-density plasmas

Characterized wakes in plasma density ramps

Abstract

Relativistic wakes produced by intense laser or particle beams propagating through plasmas are being considered as accelerators for next generation of colliders and coherent light sources. Such wakes have been shown to accelerate electrons and positrons to several gigaelectronvolts (GeV), with a few percent energy spread and a high wake-to-beam energy transfer efficiency. However, complete mapping of electric field structure of the wakes has proven elusive. Here we show that a high-energy electron bunch can be used to probe the fields of such light-speed wakes with femtosecond resolution. The highly transient, microscopic wakefield is reconstructed from the density modulated ultra-short probe bunch after it has traversed the wake. This technique enables visualization of linear wakefields in low-density plasmas that can accelerate electrons and positrons beams. It also allows characterization of wakes in plasma density ramps critical for maintaining the beam emittance, improving the energy transfer efficiency and producing high brightness beams from plasma accelerators.