Narrow bandwidth, low-emittance positron beams from a laser-wakefield accelerator

TL;DR

This paper demonstrates the first experimental generation of high-quality, ultra-relativistic positron beams from a laser-driven source, enabling future plasma-based positron acceleration for high-energy colliders.

Contribution

It provides the first experimental evidence of a laser-driven positron source suitable for injection into plasma accelerators, with detailed characterization and simulation support.

Findings

Positron beams with >10^5 particles at 600 MeV energy

Spectrally narrow (5%) and femtosecond duration

Micron-scale normalized emittance

Abstract

The rapid progress that plasma wakefield accelerators are experiencing is now posing the question as to whether they could be included in the design of the next generation of high-energy electron-positron colliders. However, the typical structure of the accelerating wakefields presents challenging complications for positron acceleration. Research in plasma-based acceleration of positrons has thus far experienced limited experimental progress due to the lack of positron beams suitable to seed a plasma accelerator. Here, we report on the first experimental demonstration of a laser-driven source of ultra-relativistic positrons with sufficient spectral and spatial quality to be injected in a plasma accelerator. Our results indicate, in agreement with numerical simulations, selection and transport of positron beamlets containing $N_{e+}\geq10^5$ positrons in a 5\% bandwidth around 600 MeV, with femtosecond-scale duration and micron-scale normalised emittance. Particle-in-cell simulations show that positron beams of this kind can be efficiently guided and accelerated in a laser-driven plasma accelerator, with favourable scalings to further increase overall charge and energy using PW-scale lasers. The results presented here demonstrate the possibility of performing experimental studies of positron acceleration in a plasma wakefield.