Structure Optimization of RF Electric Focused Drift Tube Linac

Abstract: [Background] The radio frequency electric focusing CH-DTL (RFC) accelerating structure integrates the CH-DTL and the four vane RFQ which have the same electromagnetic field mode as TE210 in the same cavity, offering the advantages of compactness, efficiency, and operational stability. This RFC design is versatile, serving as an intermediate transition structure between an RFQ and the main acceleration section in large linear accelerators or as a suitable configuration for smaller accelerator systems in medical and industrial applications, demonstrating promising potential. [Purpose] To enhance the RF efficiency and operational stability of the RFC while reducing its fabrication complexity, a systematic optimization of its RF structure was undertaken. [Methods] Proceeding in sequential order from the acceleration unit to the entire cavity, and employing the equivalent circuit method, optimizations are carried out on the CH-DTL module, the RFQ section, the transition unit, and ultimately, the entire cavity. This systematic approach aims at striking a balance between performance enhancement and manufacturing practicality. [Results] Finally, based on the optimization results, the design of 162.5MHz RFC power cavity is completed. The effective accelerating gradient of the cavity reaches 1.6 MV/m, the effective shunt impedance is 46 MΩ/m, and it has good process feasibility and cooling performance. [Conclusions] This research work will promote the development of RFC accelerating structure, and can also provide a reference for similar types of resonant cavity design.