Beam Dynamics Investigation of the 101.28 MHz IH Structure as Injector for the HIE-ISOLDE SC Linac

The first phase of the HIE-ISOLDE project at CERN consists of a superconducting (SC) linac upgrade in order to increase the energy of post-accelerated radioactive ion beams from 2.8 MeV/u to over 10 MeV/u (for A/q = 4.5). In preparation for the upgrade, we present beam dynamics studies of the booster section of the normal conducting (NC) REX-ISOLDE linac, focused on the longitudinal development of the beam in the 101.28 MHz Interdigital H-mode Structure (IHS), employing a Combined Zero Degree Structure (KONUS), pulsing at a high gradient of over 3 MV/m. The evolution of the transverse emittance in the SC linac depends critically on the injected longitudinal phase space distribution of particles from the existing linac and, with a better understanding of the beam dynamics upstream, the performance of the upgrade can be optimised. Data taken during the commissioning phase of the REX-ISOLDE linac is analysed to understand the properties of the beam in the booster and combined with beam dynamics simulations which include the realistic fields of the IHS, determined from both simulation and perturbation measurement.