Recombination of D+ and He+ ions with low-energy free electrons

We have measured the rate coefficients for the recombination of D+ ions with free electrons in the electron cooler of the storage ring CRYRING, as a function of the relative energy in the interval from 0 to ∼10 eV. Also measured is the rate coefficient for He+-e recombination at zero relative energy. The experimental data are reported at two different transverse temperatures of the electron beam, namely, 0.1 and 0.01 eV/k. The present data are compared with calculations for radiative recombination, which is expected to be the dominant recombination process for our experimental conditions. The calculations of the rate coefficients are performed using the nonrelativistic dipole approximation represented by the semiclassical Kramers approximation, corrected by the Gaunt factor. The measured rate coefficients are systematically higher than the theoretical predictions for radiative recombination, corrected for field-ionization effects in the dipole magnets of the ring. Other contributions to the recombination rate, i.e., collisional-radiative recombination and radiative stabilization, are discussed