Development of a compact 325 MHz proton interdigital H -mode drift tube linac with high shunt impedance

This paper describes the construction, rf measurement and tuning, rf conditioning, and beam commissioning of a compact 325 MHz interdigital $H$-mode (IH) drift tube linac (DTL) with modified KONUS (Kombinierte Null Grad Struktur, combined zero-degree structure) beam dynamics at Tsinghua University. This IH-DTL accelerates a proton beam from 3 MeV to 7 MeV in about 1 m. With a high rf frequency of 325 MHz, the cavity is designed to be compact while retaining a high average gradient of $4\text{ }\text{ }\mathrm{MV}/\mathrm{m}$. The efficient shunt impedance $Z{T}^{2}$ is $101\text{ }\text{ }\mathrm{M}\mathrm{\ensuremath{\Omega}}/\mathrm{m}$. The beam test results show good agreement with the beam dynamics design. The developed compact IH-DTL can be applied to the injectors of medical proton machines.