Beam Dynamics Studies of the ISOLDE Post-accelerator for the High Intensity and Energy Upgrade

The High Intensity and Energy (HIE) project represents a major upgrade of the ISOLDE (On-Line Isotope Mass Separator) nuclear facility at CERN with a mandate to significantly increase the energy, intensity and quality of the radioactive nuclear beams provided to the European nuclear physics community for research at the forefront of topics such as nuclear structure physics and nuclear astrophysics. The HIE-ISOLDE project focuses on the upgrade of the existing Radioactive ion beam EXperiment (REX) post-accelerator with the addition of a 40MVsuperconducting linac comprising 32 niobium sputter-coated copper quarter-wave cavities operating at 101.28 MHz and at an accelerating gradient close to 6 MV/m. The energy of post-accelerated radioactive nuclear beams will be increased from the present ceiling of 3 MeV/u to over 10 MeV/u, with full variability in energy, and will permit, amongst others, Coulomb interaction and few-nucleon transfer reactions to be carried out on the full inventory of radionuclides available at ISOLDE. In this thesis the beam dynamics of the superconducting linac is studied with a focus on identifying and mitigating the sources of beam emittance dilution. Highlights include the suppression of a parametric resonance, compensation of the beam-steering effect intrinsic to quarter-wave cavities and a study of the energy change in the cavities well below their geometric velocity using second-order transit-time factors. The studies lead to the specification and tolerances for the linac components. An extensive investigation of REX was also carried out involving rf and beam measurements that facilitated the benchmarking of the beam dynamics codes that were used to design the matching sections and ensure the compatibility of the upgrade. In addition, a solid-state diagnostics system was developed as a tool to aid the quick and eventually automated tuning of the large number of cavities that will accompany the upgrade.