Trapping and acceleration of spin-polarized positrons from γ photon splitting in wakefields

Abstract

Energetic spin-polarized positrons are very useful for forefront research such as e^{−}e^{+} collider physics, but it is still quite challenging to generate such sources. Here, we propose an efficient scheme of trapping and accelerating polarized positrons in plasma wakefields. By developing a fully spin-resolved Monte Carlo method, we find that in the nonlinear Breit-Wheeler pair production the polarization of intermediate γ photons significantly affects the pair spin polarization, and ignoring this effect would result in an overestimation of the pair yield and polarization degree. In particular, seed electrons colliding with a bichromatic laser create polarized γ photons which split into e^{−}e^{+} pairs via the nonlinear Breit-Wheeler process with an average (partial) positron polarization above 30% (70%). Over 70% of positrons are then trapped and accelerated in the recovered wakefields driven by a hollow electron beam, obtaining an energy gain of 3.5 GeV/cm with slight depolarization. Our method provides the potential for constructing compact polarized positron sources for future applications and may also attract broad interest in strong-field physics, high-energy physics, and particle physics.