Open Access

This dissertation presents the development of a new radio frequency quadrupole (RFQ) structure of the 4-rod type with an operating frequency of 108 MHz for the acceleration of heavy ions with mass-to-charge ratios of up to 8.5 at high duty cycles up to CW operation ("continuous wave") at the High Charge Injector (HLI) of the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt. The need to develop a completely new RFQ for the HLI arises from the fact that with the previously designed and built 4-rod RFQ structure, which was commissioned at the HLI in 2010 as part of the planned HLI upgrade program, the desired operating modes in both pulsed and CW operation could not be achieved even after several years of operating experience and considerable efforts to eliminate or at least mitigate the severe operational instabilities. Mechanical vibrations of the electrodes, which result in strong modulated power reflection, as well as the high thermal sensitivity proved to be particularly problematic. In addition to the RF design of the new RFQ by simulations performed with the CST Microwave Studio software, the focus of the investigations fell on the mechanical analysis of vibrations on the electrode rods caused by RF operation, for which the ANSYS Workbench software was used. Due to the high thermal load of the RFQ structure of more than 30 kW/m in CW operation, an accurate analysis of the thermal effects on electrode deformation as well as resulting frequency detuning of the resonator is also required, which was investigated by simulations within the capabilities of CST Mphysics Studio. Based on the results of the design studies carried out by simulations and the thereby achieved design optimizations, a 4-rod RFQ prototype with 6 stems was finally manufactured, on which most of the properties expected from the simulations could be validated by measurements of the RF characteristics as well as of the vibration behavior. Finally, based on the results of the pre-tests and considering a newly developed beam dynamics concept, a completely revised RF design for a new full-length HLI-RFQ was derived from the prototype design.