Beam Dynamics Studies of a Multi-harmonic Buncher for 10 MHz Post-accelerated RIBs at HIE-ISOLDE

A comprehensive beam dynamics study was carried out to assess the performance of a proposed bunching system at HIE-ISOLDE to increase the bunch spacing of post-accelerated radioactive ion beams by a factor of 10 to approximately 100 ns. In this note different layout options are presented that are based on a multi-harmonic buncher (MHB) with a fundamental sub-harmonic frequency of 10.128 MHz placed upstream of the REX-ISOLDE RFQ. The electrode geometry of the MHB is specified along with the required rf phase and voltage stability, and the transfer line between the ion source and RFQ including the MHB is designed and simulated. It is shown that for minimal losses in transmission a 10.128 MHz beam can be delivered to the experiments with only a slight degradation in beam quality. In certain scenarios the longitudinal emittance could be reduced significantly.