Polarized proton acceleration in ultra-intense laser interaction with near critical density plasmas

TL;DR

This study demonstrates the potential for producing polarized proton beams with multi-GeV energies through ultra-intense laser interactions with near-critical density plasmas, analyzing polarization dynamics and acceleration efficiency.

Contribution

It introduces a novel simulation-based analysis of polarized proton acceleration in near-critical plasmas, including polarization dynamics and species ratio effects.

Findings

Protons can be efficiently accelerated if their fraction is below 20%.

Proton polarization can be altered by laser and wakefield magnetic fields.

Large bubble sizes facilitate higher energy proton acceleration.

Abstract

The production of polarized proton beams with multi-GeV energies in ultra-intense laser interaction with targets is studied with three-dimensional Particle-In-Cell simulations. A near-critical density plasma target with pre-polarized proton and tritium ions is considered for the proton acceleration. The pre-polarized protons are initially accelerated by laser radiation pressure before injection and further acceleration in a bubble-like wakefield. The temporal dynamics of proton polarization is tracked via the T-BMT equation, and it is found that the proton polarization state can be altered both by the laser field and the magnetic component of the wakefield. The dependence of the proton acceleration and polarization on the ratio of the ion species is determined, and it is found that the protons can be efficiently accelerated as long as their relative fraction is less than 20%, in which case the bubble size is large enough for the protons to obtain sufficient energy to overcome the bubble injection threshold.