Classical dynamics of enhanced low-energy electron-ion recombination in storage rings

Electron-ion recombination observed in storage ring experiments shows a strong enhancement of the recombination rate for highly charged ions with low-energy electrons relative to what standard radiative recombination rates predict. We present detailed simulations of the toroid and solenoid regions of the electron cooler, analyzing the classical dynamics of an electron in the presence of the Coulomb field of the ion, the homogeneous magnetic field inside the cooler, and the transient electric field in the merging section. Both bound and continuum electron dynamics display partially chaotic motion. For bound states we observe stochastic and quasiperiodic l mixing while for continuum electrons we find transient chaos characterized by a fractal generalized reflection function. We determine the modified radiative and field-induced recombination of the electron with a highly charged ion in a storage ring. The obtained absolute excess recombination rates are compared with the experimental data and, overall, reasonable agreement is found. The scaling of the rate with the average relative energy, the ion charge, the magnetic guiding field, and the electron-beam temperatures is analyzed