Design and Preliminary Tests of the IH-DTL II for Heavy Ion Therapy

The Chinese Academy of Sciences Heavy Ion Medical Research Center (CASHIM), in collaboration with Sun Yat-sen University, has developed a linear injector for a new generation of domestically produced heavy ion therapy facilities. The injector consists of a radio frequency quadrupole (RFQ) followed by two interdigital H-mode drift tube linacs (IH-DTLs), capable of providing C 4 + beams with an energy of 7 MeV/u. The RFQ and IH-DTL I cavities are fabricated and tested, and the test results meet the design specifications. The IH-DTL II adopts an alternating phase focusing (APF) scheme, which eliminates transverse focusing elements and enables a compact cavity structure. It accelerates C 4+ beams from 4 MeV/u to 7 MeV/u at an operating frequency of 200 MHz, achieving a transmission efficiency of 100% and an energy spread below 0.5%. The cavity is designed with a Kilpatrick ( Kp ) factor of 1.65 to mitigate the risk of voltage breakdown and exhibits a quality factor ( Q ) of approximately 17,000. The IH-DTL II cavity has been successfully fabricated, and both cold tests and preliminary beam energy measurements have been completed. This paper presents the detailed design and experimental results of the IH-DTL II.