Characterizing ultralow emittance electron beams using structured light fields

Andreas Seidel,Matt Zepf,Jens Osterhoff

doi:10.1103/physrevaccelbeams.24.012803

Abstract

Novel schemes for generating ultra-low emittance electron beams have been developed in the last years and promise compact particle sources with excellent beam quality suitable for future high-energy physics experiments and free-electron lasers. Current methods for the characterization of low emittance electron beams such as pepperpot measurements or beam focus scanning are limited in their capability to resolve emittances in the sub $0.1$ mm mrad regime. Here we propose a novel, highly sensitive method for the single shot characterization of the beam waist and emittance using interfering laser beams. In this scheme, two laser pulses are focused under an angle creating a grating-like interference pattern. When the electron beam interacts with the structured laser field, the phase space of the electron beam becomes modulated by the laser ponderomotive force and results in a modulated beam profile after further electron beam phase advance, which allows for the characterization of ultra-low emittance beams. 2D PIC simulations show the effectiveness of the technique for normalized emittances in the range of $\epsilon_n=[0.01,1]$ mm mrad.

Highlights

The emittance of an electron beam is one of its most important quality measures for many applications
Novel schemes for generating ultralow emittance electron beams have been developed in past years and promise compact particle sources with excellent beam quality suitable for future high-energy physics experiments and free-electron lasers
When the electron beam interacts with the structured laser field, the phase space of the electron beam becomes modulated by the laser ponderomotive force and results in a modulated beam profile after further electron beam phase advance, which allows for the characterization of ultralow emittance beams. 2D PIC simulations show the effectiveness of the technique for normalized emittances in the range of εn 1⁄4 1⁄20.01; 1 mm mrad

Summary

INTRODUCTION

The emittance of an electron beam is one of its most important quality measures for many applications. Significant improvements in radio-frequency (rf) guns with laser photocathodes allow a small initial source size and limit the emittance growth in the early stages using strong accelerating fields of several tens of MV/m Using this approach GeV level linear accelerators (linacs) currently achieve a normalized transverse emittance εn 1⁄4 βeγeε (βe 1⁄4 ve=c, γe—electron gamma factor, and ε—geometric beam emittance) of 0.002 mm mrad [3]. Measurements of small spatial scales with laser interference structures is a viable approach to assess the quality of electron beams and has been demonstrated in beam-size monitors, where in contrast to wire scanners the fine wire is replaced by a “laser-wire” formed by interfering lasers in the so-called Shintake monitor [16] It can resolve nm-spatial scale electron beam foci using a scanning technique. While this method requires a measurement of the electron bunches at focus, which can be an immense effort for polychromatic electron beams, our proposal is compatible with broadband diverging beams and allows a determination of the slice emittance

THEORETICAL MODEL

SIMULATION RESULTS

CONCLUSION