Abstract
A novel scheme is proposed for generating a polarized positron beam via multiphoton Breit-Wheeler process during the collision of a 10 GeV, pC seeding electron beam with the other 1 GeV, nC driving electron beam. The driving beam provides the strong self-generated field, and a suitable transverse deviation distance between two beams enables the field experienced by the seeding beam to be unipolar, which is crucial for realizing the positron polarization. We employ the particle simulation with a Monte-Carlo method to calculate the spin- and polarization-resolved photon emission and electron-positron pair production in the local constant field approximation. Our simulation results show that a highly polarized positron beam with polarization above $40\%$ can be generated in several femtoseconds, which is robust with respect to parameters of two electron beams. Based on an analysis of the influence of $\gamma$-photon polarization on the polarized pair production, we find that a polarized seeding beam of the proper initial polarization can further improve the positron polarization to $60\%$.
Highlights
Polarized positron beams are indispensable tools in many areas of science and technology
The field experienced by the seeding beam can be unipolar by incorporating a proper impact parameter, which is crucial to realizing the positron polarization
The positron polarization degree can be further increased to 60% provided the seeding beam is initially polarized
Summary
Polarized positron beams are indispensable tools in many areas of science and technology. The magnetic field in the rest frame of the seeding beam is approximately along one direction, which is a key factor for the spin polarization of both primary electrons of the seeding beam and the newly generated e−e+ pairs. The equivalent validity condition of LCFA is a0∗ ≈ 2|e|Ermax d /π mec , i.e., a0∗
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