EM and Thermo-Mechanical Analysis and Design of a Compact-RFQ

The design and optimization of a Radio-Frequency Quadrupole (RFQ) for focusing, bunching and accelerating charged particles needs to simultaneously deal with electromagnetic, thermal and mechanical issues to achieve a fully operational structure. Four resonant cavities along the RFQ together with the ending cut backs have to provide a quadrupolar mode at the desired frequency and to produce a flat transversal electrical field amplitude across the overall length of the structure. The operation of an RFQ needs the injection of a very high RF signal power, so a high quality factor Q and appropriate handling of thermal losses is mandatory. A water-cooling circuit is commonly employed inserted in between the resonant lobes, close to the vane tips. On the other hand, RF and vacuum ports have to introduce minimal perturbations in the structure and, finally, a number of RF signal pick-ups and tuners are added to test and adjust the RFQ performance. The complexity of such structure together with the mechanical feasibility with required accuracy and tunability options is even more challenging when dealing with compact RFQ designs. The paper describes the EM and thermo-mechanical design and optimization of a compact RFQ intended for proton acceleration. The main aspects in this work are linked to the RFQ compactness and with the novel RF signal injection design.