  The dynamics of electrons in counter-propagating, circularly polarized laser
beams are shown to exhibit attractors whose ability to trap particles depends
on the ratio of the beam intensities and a single parameter describing
radiation reaction. Analytical expressions are found for the underlying limit
cycles and the parameter range in which they are stable. In high-intensity
optical pulses, where radiation reaction strongly modifies the trajectories,
the production of collimated gamma-rays and the initiation of non-linear
cascades of electron-positron pairs can be optimized by a suitable choice of
the intensity ratio.
