Generation of Ultrabrilliant Positron Beam via Superponderomotive Injection in Laser Wakefield Acceleration

Plasma-based acceleration of positrons attracts extensive interests due to the ultrahigh accelerating gradient and ultrashort duration, while generating wakefield positron beam by the inherent injection is still a great challenge. Here, we put forward a superponderomotive injection method of positrons in the blowout regime of laser wakefield acceleration. In this method, transverse laser fields facilitate the trapping of positrons into the laser-modulated longitudinal wakefield which dominates the subsequent energy gaining, that is distinct from the electrostatic induced superponderomotive electrons. Particle-in-cell simulations demonstrate that this method can be implemented by the collision between a donut wake and a pair jet, resulting in the multi-cycle positron beam with hundreds of pC charge and brightness of $10^{13}~\rm{Am}^{-2}$. Such a collisional setup is available in the current laser-plasma experiments, and the generated positron beam is favorable for developing next generation of electron-positron collider, modeling the laboratory astrophysics and performing the ultrafast material diagnostics research.