Development of RF accelerating structures in the front-end system of light ion particle accelerators

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) is an RF linear accelerator-based neutron source which utilizes various RF cavity resonators to interact with a traveling particle beam to transfer energy to the beam. The RF cavity resonator generates a strong electromagnetic modal field specifically shaped at an operating frequency to provide good energy efficiency. Having a reliable cavity RF field is therefore, important to sustain performance and stable operation of the accelerator system. Although the SNS system is already built and in use, some parts still need to be improved to achieve better performance and higher operational reliability. Our study can provide potential improvements in existing accelerators as well as future ones. For example, the performance and reliability of the radio frequency quadrupole (RFQ) and the rebuncher cavities in the low beam energy front-end section of the SNS accelerators, have been improved by applying our newly proposed design ideas. In this dissertation, we propose four development directions for RFQ and rebuncher cavity to enhance its performance and field stabilization. These include: 1) a practical design method to determine RFQ fabrication tolerance based on extensive 3D simulations to help reduce RFQ fabrication errors. 2) alternative RFQ designs to improve RFQ mode separation with lower fabrication, tuning costs and structural reliability. 3) a multi-section RFQ with new RF coupling scheme which is validated with scaled prototyping. This design eliminates spurious electromagnetic modes and can decrease manufacturing and tuning costs of long coupled RFQs. 4) a double gap rebuncher cavity design instead of a single cavity for decreased gap voltage and peak electric field. This design modification can reduce X-ray radiation intensity which can address safety problems in the current accelerator front-end area. A summary of our proposed solutions and contributions are presented in this dissertation paper.