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Abstract

Merged beams experiments on inelastic electron-ion collisions in ion storage rings can reach very high energy resolution and offer fine control of the collision partners. To optimize the energy resolution, an electron target* was installed at the TSR in addition to the e-cooler. This made it possible to perform electron collision experiments at variable relative energy avoiding the resolution loss caused by the interruption of electron cooling. Furthermore, a strong gain in energy resolution was obtained by using a cryogenic electron source** developed for the TSR target. Here, a GaAs photocathode provides dc electron currents up to about 0.5 mA with an emission energy spread of about 10 meV. In first recombination measurements using this source, performed on HD+, H3+ and Sc18+, low energy resonant structures at milli-eV collision energies revealed unprecedented low transverse and longitudinal electron temperatures of about 0.5 meV and 0.025 meV, respectively. In this talk the performance of the TSR ultra-cold electron target is presented. In addition, the perspectives of photocathode-driven electron coolers operating at very low laboratory energies are discussed.