After injection into the ESR storage ring, the hot ion beam is cooled via Coulomb interaction with the monoenergetic electron beam of the electron cooler, resulting in a low beam emittance of about 0.1 π mm and a very narrow momentum distribution of about Δp/p = 10^-5. Besides its application as a cooling device, the ESR electron cooler also serves as an electron target, allowing for recombination experiments at near-zero relative velocities.

Layout of the ESR electron cooler: Electrons produced at a cathode temperatur of about 1300 K are guided by a 0.1 T magnetic field to overlapp with the ion beam on a range of about 2 m.

Schottky spectrum of the ion bam before and after electron cooling is applied.

Typical experimental setup for X-ray spectroscopy experimentens at the ESR electron cooler: X-Ray detectors are located at angles of approximatly 0 and 180 degree with respect to the ion beam axis. Like at the gas target, a particle detector after the next dipole magnet allows for coincidence measurements.