IH-DTL design with modified KONUS beam dynamics for a synchrotron-based proton therapy system

A modified Kombinierte Null Grad Struktur (KONUS) beam dynamics for inter-digital H-mode (IH) drift tube linac (DTL) is proposed in this study. This modified KONUS beam dynamics, which is aperiodic and is suitable for a short (<1 m) DTL design, is applied to a dedicated 325 MHz IH-DTL design at Tsinghua University. The IH-DTL, which is utilized in the injector of a synchrotron-based proton therapy system, is divided into three sections, namely, rebunching (-80 degrees), 0 degrees acceleration, and debunching (10 degrees). It is slightly different from the conventional KONUS cavity, and no focusing magnets exist in the cavity to reduce the cost of fabrication. The presence of 21 gaps in the cavity can accelerate a 15 mA proton beam from 3 MeV to 7 MeV. The cavity is tapered to adjust the gap voltage distribution, and the inner diameter varies from 196.8 mm to 232.6 mm. A cavity length of 1 m has a theoretical power consumption of 151 kW, whereas the maximum surface electric field is 40 MV/m (2.3 Kp). A new design process, which is similar to alternating-phase focusing method, is proposed. Details of the design method and results are presented in this study.