Particle Drifts and Radiation Reaction in Astrophysics

In the presence of strong electromagnetic fields, the energy radiated by accelerated relativistic charged particles becomes comparable to their kinetic energy. Under such conditions, radiation reaction, i.e., the recoil charges experience when radiating, must be taken into account to correctly describe particle motion. Earlier results have shown that, in the radiative regime, initially stable relativistic plasmas subject to a strong uniform magnetic field will develop ring-shaped momentum distributions with inverted populations.

These distributions are unstable to maser-type kinetic instabilities capable of coherent radiation, whose properties align to those observed in pulsars and Fast Radio Bursts. In this thesis, we generalize the previous result to account for other non-uniform configurations of the electromagnetic fields. First, we investigate single particle dynamics and derive the equations of motion for the guiding center of a particle in the radiative regime. Second, we study the effects of a drift velocity, with an emphasis on the curvature drift, on the momentum distribution of a radiatively cooled plasma.

Our findings show that plasmas will develop spiral momentum distributions if the drift velocity is high enough. Criteria for the different regimes are determined. Lastly, we study beam-plasmas undergoing radiative cooling as they travel along the field lines of a static magnetic dipole.

Our results are corroborated via test particle simulations employing a fully-parallelized pusher using the Landau-Lifshitz model for classical radiation reaction, developed for this thesis. We conjecture the physics explored here is relevant in providing intuition for the dynamics of astrophysical plasmas and for coherent radiation generation.