Tail-Wave-Assisted Positron Acceleration in Nonlinear Laser Plasma Wakefields

Abstract

Relativistic laser-wakefield acceleration is characterized by an unsurpassed accelerating gradient, which is very suitable for electron acceleration over short distances and could be a promising candidate for next-generation compact accelerators. However, using this technique for positron acceleration remains challenging because positively charged particles are commonly defocused in the accelerating structure of a standard nonlinear wakefield driven by an ultrashort laser pulse. Here we propose and numerically demonstrate a scheme to accelerate an externally injected positron beam in a nonlinear laser wakefield in a regime where a tail wave is formed behind density cusps of the wakefield. This tail wave can provide a focusing force in addition to longitudinal acceleration for the positrons. Three-dimensional particle-in-cell simulations demonstrate that a trapping efficiency of positrons of nearly 100% in the nonlinear wakefield is possible. This scheme may open a simple way to achieve compact positron acceleration of hundreds of MeV at high repetition rates with terawatt-class laser systems without the need for special laser modes and plasma structures.