Formation of GeV-level collimated linear Breit-Wheeler positron beams by experimentally available laser pulses and targets

Motivated by the experimental capability of newly constructed laser facilities and the developments in target fabrication, it has been previously shown [Comm. Phys. 4, 139 (2021)], by using a post-processing algorithm, that over 10⁸ electron-positron pairs can be created by the linear Breit-Wheeler (BW) process by two laser pulses with the intensity of the order of 10²² W/cm² colliding inside a structured plasma channel. However, the dynamics of these created linear BW positrons is yet to be examined. By using a random pairing method, we have successfully implemented the linear BW process into the particle-in-cell code EPOCH. From the numerical simulations, we found that the linear BW positrons can be accelerated by the remaining laser pulses to GeV-level energies, and confined by the azimuthal plasma magnetic fields to form collimated energetic positron beams. The formation of such linear BW positron beams is likely to facilitate the experimental observation of the linear BW positrons, and also indicates that such an experimental setup has the potential to serve as energetic positron source in future experiments.