Preview

PDF, English Download (8MB) | Terms of use

Abstract

Charged particles emit electromagnetic radiation when accelerated, and the subsequent impact on the trajectory must be accounted for by energy and momentum conservation in a self-consistent equation of motion, such as the Landau-Lifshitz (LL) equation. This effect, known as radiation reaction (RR), becomes significant for relativistic particles in the presence of extremely strong electromagnetic fields, such as an intense laser pulse or pulsar magnetosphere. The LL equation is typically solved either analytically, while treating each particle independently in an external field, or numerically, with a mean field generated by a charge distribution in addition to an external field, as in particle-in-cell (PIC) codes. Yet, the first approach is in principle inconsistent, while the latter neglects the point-like nature of particles which gives rise to RR. We extend the LL equation in its reduced form to include the Lienard-Wiechert fields from neighbouring particles, which is solved numerically for the first time, to our knowledge. For the collision of a relativistic electron-positron bunch with an intense laser pulse, we identify a regime in which micro-bunches are created by the reflected radiation, which leads to coherent emission across a broad range of frequencies in the X-ray domain, in which RR can play a significant role. A similar, coherently enhanced RR is also observed in a constant and uniform magnetic field, with a weaker form of micro-bunching. In both cases, this `collective RR' coincides with a phase space expansion and is therefore transient.