Charge breeding of CO$^{+}$ beams at REX-ISOLDE

The β+ emitter 11C is a possible treatment ion for hadron therapy owing to its excellent properties in PET imaging, which could be used for range verification during the treatment. A charge breeder is required to transform the molecular CO+ beam, coming from an ISOL-production stage (Isotope Separation OnLine), to Cn+ and to match it with the acceptance of the medical accelerator. At REX-ISOLDE we have tested charge breeding of stable, molecular 13CO+ beams. Efficiencies for the normal REX operation scheme including a Penning trap and an Electron Beam Ion Source (EBIS) as well as for continuous injection into the EBIS without prior cooling and bunching in the trap are presented. We have in more detail explored molecular break-up in the buffer gas of the Penning trap and loss-mechanisms in the EBIS. Several 107 C6+ ions per pulse could be extracted, however, based on the present measurements, we also discuss possibilities for the future to increase the output and efficiency of the charge breeder.