Higher order terms of radiative damping in extreme intense laser-matter interaction

The higher order terms of the Lorentz-Abraham-Dirac equation have been derived, and their effects are studied via a relativistic collisional particle-in-cell simulation. The dominant group of terms up to the fourth order of the Lorentz-Abraham-Dirac equation is identified for ultra-intense laser-matter interactions. The second order terms are found to be the damping terms of the Lorentz force while the first order terms represent friction in the equation of motion. Because the second order terms restrict electron acceleration during the laser interaction, electrons/ions are prevented from over-accelerating. Radiative damping becomes highly significant when I≥ 1022 W/cm2 while Bremsstrahlung will be saturated, thus radiative damping will be a dominant source of hard x-rays in regimes at extreme intensities.