Multiple self-injection in the acceleration of monoenergetic electrons by a laser wake field

Multiple electron self-injection in laser wake-field acceleration is studied via fully relativistic two- and three-dimensional particle-in-cell simulation. The electron density modulation in the laser wake originating from oscillations of the laser pulse waist and relativistic effects can provoke the parametric resonance in the electron fluid momentum. This may result in repetitive trapping of plasma electrons in the acceleration phase of the laser wake: multiple electron self-injection. The maximal energy of the accelerated electrons depends strongly on the total charge of the injected electrons. A low energy spread, less than 1%, for an almost 1GeV energy electron beam with charge about 10pC is found numerically in the plasma channel irradiated by a 25TW laser pulse, while a 200TW laser pulse produces a few nC beam with only 150MeV energy. Essentially thermalization of accelerated electrons is also a result of charge loading.