Residual Gas Ions Characterization from the REXEBIS

The Isotope mass Separator On-Line DEvice (ISOLDE) is a user facility located at CERN where Radioactive Ion Beams (RIBs) are produced from proton collisions onto a target, mass separated and transported to user experimental stations either directly at low energy or after being post- accelerated, notably for nuclear physics studies. Prior to acceleration through the REX/HIE-ISOLDE linear accelerator, the ion beam is accumulated, bunched and cooled in a Penning trap (REXTRAP) and afterwards charge-bred in an Electron Beam Ion Source (REXEBIS). Multi-charged radioactive species of interest are then selected by a mass-to- charge (A/q) ratio separator dipole in the Low Energy Beam Transfer Line (LEBT). A method is presented to character- ize the Residual Gas Ion (RGI) background contamination for different operational conditions of the REXEBIS. More particularly, a discussion is held about the influence of the confinement time inside the charge-breeder on the residual gas spectrum. Finally, a method to identify sub-pico-Ampere contaminants is demonstrated.