Charge Breeding Techniques

The numerous newly built and forthcoming post-accelerators for radioactive ions, produced with the isotope separator on-line (ISOL) technique, all have a need for an efficient method to accelerate the precious primary ions. By increasing the ion charge-to-mass ratio directly after the radioactive ion production stage, a short and compact linear accelerator can be employed. Not only the efficiency, but also the rapidity of such a charge-to-mass increasing process, called charge breeding, is a crucial factor for the often short-lived radioisotopes. The traditional foil or gas stripping technique was challenged some five to ten years ago by novel schemes for charge breeding. The transformation from 1+ to n+ charged ions takes place inside an Electron Beam Ion Source/Trap (EBIS/T) or Electron Cyclotron Resonance Ion Source/Trap (ECRIS/T) by electron-ion collisions. These charge breeders are located in the low-energy part of the machine before the accelerating structures. Because of the capability of these devices to produce highly charged ions, mass-to-charge ratios between 4 and 9 are easily obtained. In this article the performance and the features of the above listed charge breeding concepts will be compared and discussed. An outlook on charge breeders for the next generation of radioactive ion beam facilities is also given. This paper is a longer version of a contribution to Radioactive Nuclear Beams 6, Argonne National Laboratory, Illinois, USA, Sept 22-26, 2003. To be published in Nucl. Phys. A