Highly spin-polarized multi-GeV electron beams generated by single-species plasma photocathodes

TL;DR

This paper demonstrates a novel plasma-based method to generate highly spin-polarized, multi-GeV electron beams using a single-species ytterbium vapor, combining simulations to achieve 56% polarization in a compact accelerator.

Contribution

It introduces a new scheme for producing and accelerating highly spin-polarized relativistic electron beams in plasma accelerators using ytterbium vapor and laser photoionization.

Findings

Achieved up to 56% net spin polarization in electron beams.

Generated 15 GeV electron beams within 41 cm of plasma.

Combined simulations to validate the scheme's effectiveness.

Abstract

High-gradient and high-efficiency acceleration in plasma-based accelerators has been demonstrated, showing its potential as the building block for a future collider operating at the energy frontier of particle physics. However, generating and accelerating the required spin-polarized beams in such a collider using plasma-based accelerators has been a long-standing challenge. Here we show that the passage of a highly relativistic, high-current electron beam through a single-species (ytterbium) vapor excites a nonlinear plasma wake by primarily ionizing the two outer 6s electrons. Further photoionization of the resultant Yb2+ ions by a circularly polarized laser injects the 4f14 electrons into this wake generating a highly spin-polarized beam. Combining time-dependent Schrodinger equation simulations with particle-in-cell simulations, we show that a sub-femtosecond, high-current (4 kA) electron beam with up to 56% net spin polarization can be generated and accelerated to 15 GeV in just 41 cm. This relatively simple scheme solves the perplexing problem of producing spin-polarized relativistic electrons in plasma-based accelerators.