The CRYRING@ESR electron cooler as internal target for atomic physics experiments

We present developments at the electron cooler of the CRYRING@ESR storage ring aimed at improving its performance as internal target in low-energy electron–ion collision experiments. We describe recent modifications of the high-voltage and vacuum systems which lead to improved electron energy control and lower background count rates during such measurements. In a benchmark experiment on dielectronic recombination of F$^{6+}$, we demonstrate that a spectroscopic resolution equivalent to transverse and longitudinal thermal electron energy spreads of $\approx$ 1 meV and $\approx$ 45 µeV, respectively, can be achieved under optimum conditions. This surpasses system performance observed previously in similar experiments.