Merged-beams collision spectroscopy at the CRYRING@ESR cooler

The CRYRING formerly located at the Manne-Siegbahn Laboratory ( in Stockholm, Sweden, is well recognized for pioneering work on precision electron-ion spectroscopy with cold (‘expanded’) electron beams. CRYRING is presently being relocated to GSI using the ESR as the primary injector. The operation of CRYRING coupled to the ESR, i.e., to a second storage ring is world-unique and offers ample exciting opportunities for new paths in electron-ion collision physics.

CRYRING@ESR features an electron cooler/target with an electron beam that is adiabatically expanded in the transverse direction. The temperatures of the are distinctively lower than than the ones at electron coolers without expansion such as the ESR cooler.

At the ESR, CRYRING is combined with a very capable injector that can deliver intense beams of heavy highly charged ions and few-electron radioisotopes. The dual-storage ring assembly provides many additional options for beam preparation and measurements.

In contrast to the ESR electron cooler, the CRYRING cooler possesses a very small electron energy-spread, in particular in transverse direction (temperatures kBT < 1.5 meV and kBT|| ≈ 0.05 meV. The longitudinal temperatures obtained with the CRYRING cooler are about a factor of 2-4 lower than those for the ESR cooler. However, through the implementation of adiabatic transverse expansion with expansion factors of up to 100, the transverse electron temperature of the CRYRING cooler is a hundred times lower than the one of the ESR cooler. The low temperatures of the electron beam lead to a vastly improved experimental resolution and a higher precision for the determination of resonance energies.