Simulation of accelerated electron spectra in laser wakefield accelerators

The generation of high quality electron beams in a laser wakefield accelerator (LWFA) is generally thought to require phased injection of an ultrashort electron bunch. However, simulations have shown that longer bunch, unphased injection may also produce high quality, short electron bunches if the injection energy is properly chosen. The process involves pruning of electrons that move into defocusing portions of the wakefield, along with strong phase bunching and rapid acceleration. Simulation results are consistent with a simple Hamiltonian model that numerically integrates particle orbits in an idealized wake potential. Simulations are also presented for a channel-guided LWFA system using optical injection.