Robust energetic positron beam production in laser-electron beam interactions

Particle accelerators require energetic positron sources to satisfy next generation requirements. Positrons are currently sourced using solid targets. Here, we consider the collision of an energetic electron beam ( ≥ 5 GeV) with an intense laser pulse ( 2 × 1 0 22 Wcm −2 ) as a potential positron beam source. Prolific pair production occurs due to strong field quantum electrodynamic effects in the interaction resulting in a high positron yield. Through the decoupling of initial and final positron energy, positrons converge towards the same average energy regardless of the initial energy they are produced at. Through 1D particle-in-cell simulations we demonstrate that positron beams with 200 MeV average energy may be generated through non-linear Breit-Wheeler pair production. By reducing the electron beam energy, the energy spread of resulting positron beam decreases by up to 38% while the final positron energy remains constant. Comparison between the simulations and the analytical model show that the simulated positrons agree with the model within 4%. The low energy spread and low shot-to-shot variation in energy make these beams ideal for injection into particle accelerators.