Conceptual design of a 714-MHz RFQ for compact proton injectors and development of a new tuning algorithm on its aluminium prototype

Radio frequency quadrupoles (RFQs), which are crucial components of proton injectors, significantly affect the performance of proton accelerator facilities. An RFQ with a high frequency of 714 MHz dedicated to compact proton injectors for medical applications is designed in this study. The RFQ is designed to accelerate proton beams from 50 keV to 4 MeV within a short length of 2 m and can be matched closely with the downstream drift tube linac to capture more particles through a preliminary optimization. To develop an advanced RFQ, challenging techniques, including fabrication and tuning method, must be evaluated and verified using a prototype. An aluminium prototype is derived from the conceptual design of the RFQ and then redesigned to confirm the radio frequency performance, fabrication procedure, and feasibility of the tuning algorithm. Eventually, a new tuning algorithm based on the response matrix and least-squares method is developed, which yields favorable results based on the prototype, i.e., the errors of the dipole and quadrupole components reduced to a low level after several tuning iterations. Benefiting from the conceptual design and techniques obtained from the prototype, the formal mechanical design of the 2-m RFQ is ready for the next manufacturing step.