Effects of Radiation Damping in Extreme Ultra-intense Laser-Plasma Interaction

Abstract

Recent advances in the development of intense short pulse lasers are significant. Now it is available to access a laser with intensity 1021 W/cm2 by focusing a petawatt class laser. In a few years, the intensity will exceed 1022 W/cm2, at which intensity electrons accelerated by the laser get energy more than 100 MeV and start to emit radiation strongly. Resultingly, the damping of electron motion can become large. In order to study this problem we developed a code to solve a set of equations describing the evolution of a strong electromagnetic wave interacting with a single electron. Usually the equation of motion of an electron including radiation damping under the influence of electromagnetic fields is derived from the Lorentz-Dirac equation treating the damping as a perturbation. So far people had used the first order damping equation. This is because the second order term seems to be small and actually it is negligible under 1022 W/cm2 intensity. The derivation of 2nd order equation is also complicated and challenging. We derived the second order damping equations for the first time and implemented in the code. The code was then tested via single particle motion in the extreme intensity laser. It was found that the 1st order damping term is reasonable up to the intensity 1022 W/cm2, but the 2nd oder term becomes ii not negligible and comparable in magnitude to the first order term beyond 1023 W/cm2. The radiation damping model was introduced using a one-dimensional particle-in-cell code (PIC), and tested in the laser - plasma interaction at extreme intensity. The strong damping of hot electrons in high energy tail was demonstrated in PIC simulations.