Characterizing Direct Laser Acceleration in the Radiation Friction Attractor Regime*

We investigate electron dynamics in direct laser acceleration (DLA) within the 'attractor' regime induced by radiation friction [New J. Phys. 23, 095010 (2021)]. DLA has been extensively studied analytically using test-electron models that exclude radiation friction, where an integral of motion, S, representing electron’s effective energy, well characterizes the electron dynamics. Previous studies have demonstrated that the inclusion of radiation friction leads to asymmetric variations in S during different phases of the electron trajectory. Over prolonged interaction periods, irrespective of the electron's initial condition, S converges towards a dynamic equilibrium value, known as the 'attractor' regime, which is determined by specific laser and plasma parameters. In this regime, a balance must be achieved between trajectory segments that increase S and those that decrease S. We leverage this additional constraint to derive the electron trajectories and energy in the 'attractor' regime based on input laser and plasma parameters.