Recombination of electrons with highly charged heavy ions at very low energies

Recombination of highly charged ions with free electrons is studied in merged-beams experiments at the UNILAC accelerator in Darmstadt and at the heavy-ion storage ring TSR in Heidelberg. Unexpected high recombination rates are observed for a number of ions at very low energies E(cm) in the electron-ion center-of-mass frame. In particular, theoretical estimates for radiative recombination are dramatically exceeded by the experimental recombination rates of U28+ ions near E(cm) = 0 eV. The observations point to a general phenomenon in electron ion recombination depending on E(cm), on the ion charge state, and possibly also on electron density, electron beam temperature, and strength of external magnetic fields.