A case study for charge state breeding of heavy ions in the storage ring, ESR

Utilizing a multi-charge state mode for the operation of the heavy ion storage ring ESR, heavy ions in the charge state q can be bred from stored ions with an original charge state q + 1 via radiative recombination in the electron cooler. Using additionally the internal gas target of the ESR, also ionization and electron capture have to be taken into account. This method was tested with Pb ions, injected as bare species (Pb82+) at 277 MeV/u into the ring. The observed evolution of the intensity for the coasting beams with different charge states is described by simple rate equations applying proper rates for the charge changing processes in the cooler and in the gas jet. Using this model, a comparison of the efficiencies of the two different methods is made, i.e. the direct accumulation of the desired charge state and the breeding technique. In the latter case, projectiles ionized in the gas target are transferred back to the Pb81+ charge state via radiative recombination in the cooler and can thus efficiently be reused.