Detailed design and study of RFQ accelerator for a carbon ion therapy system

Carbon ion therapy is an effective treatment modality for specific types of tumor. The high-energy ions required for treatment are typically accelerated by a multi-stage acceleration system, which includes both low-energy linac injector and high-energy synchrotron . This paper presents a comprehensive design of the radio frequency quadrupole (RFQ) accelerator for 12 C 4+ ion therapy system, encompassing both the beam dynamics and the RF electromagnetic design. The dynamics design results reveal that the 2.6-m-long RFQ achieves a transmission efficiency of 95.5 % with an inter-vane voltage of 55 kV, effectively accelerating 12 C 4+ beam to an energy of 0.6 MeV/u. Furthermore, error analysis provides curves of Twiss parameters of the mismatched beam and compares them with the contour lines of transmission efficiency. For the RF structure, a detailed design from two-dimensional to three-dimensional structure of the cavity was carried out. In order to get more realistic results, whole cavity simulation with modulation at the tips of vanes is performed, and the result shows that the field is in good agreement with the theoretical design. The design employs dipole stabilization rods (DSRs) to separate neighboring dipole modes, and the precise influences of these neighboring modes on the operating mode have been thoroughly discussed. To achieve best dipole mode symmetry, it has been found that the length of the DSRs for the cavity with modulated vanes needs to be modified to 185 mm compared to the case without modulated vanes, which is a point that has received limited attention in the existing research. Furthermore, the frequency separation of 4.8 MHz observed with modulated vanes is superior to the 4.3 MHz separation found in the absence of modulation. • Curves of Twiss parameters of the mismatched beam are presented in error analysis. • A thorough simulation is performed to determine the RF structure of the cavity. • The influence of interference modes is quantitatively analyzed from a novel perspective. • The impact of vane tip modulation on cavity performance is clarified. • The length of the dipole rods requires adjustment compared to the common design when vane modulation is applied.