Design of the High Beta Cryomodule for the HIE-ISOLDE Upgrade at CERN

The major upgrade of the energy and intensity of the existing ISOLDE and REX-ISOLDE facilities at CERN will require the replacement of most of the existing ISOLDE post-acceleration by a superconducting linac based on quarter-wave resonators. The first stage of this upgrade involves the design, construction, installation and commissioning of two high- cryomodules downstream of REX, the existing post-accelerator. Each cryomodule houses five high-beta superconducting cavities and one superconducting solenoid. As well as providing optimum conditions for physics, where the internal active components must remain aligned within tight tolerances, the cryomodules need to function under stringent vacuum and cryogenic conditions. To preserve the RF cavity performance their assembly and sub-system testing will need to be carried out using specifically designed tooling in an ISO class 5 (US Fed. class 100) clean-room. We present the determining factors constraining the design of the high-beta cryomodules together with the design choices that these factors have imposed.