Laser-wakefield accelerator source of positron beams suitable for plasma accelerator injection*

As laser wakefield acceleration matures as a technology, the use of these accelerators for applications previously only accessible through conventional accelerator facilities is being increasingly explored by international research efforts. One of these applications is the use of a plasma wakefields to accelerate positrons to energies sufficient to use in high-energy collider experiments. Beyond the linear wakefield regime, positron injection and acceleration in plasma wakefields presents a particular challenge that requires relatively narrow bandwidth and low-emittance positron beams. These requirements that have thus limited results of positron acceleration via wakefield acceleration. In this work, we report an experimental demonstration of a laser-driven electron converter source of GeV-scale positron beams with spectral and emittance quality suitable to be used as an injection seed in a wakefield accelerator. Numerical simulations agree with the measured beams and show transport of beams containing N_e+ ≥ 10⁵ positrons in a 5% bandwidth around 600 MeV with femtosecond-scale duration and micron-scale normalized emittance. Particle-in-cell simulations show that the positrons as measured in experiment may be efficiently injected into a laser wakefield accelerator for subsequent acceleration after production.