Beam dynamics and cavity design of an 8 MeV CW IH-DTL for SYSU-PAFA

Abstract

Abstract As a part of the Particle Accelerator Facility at Sun Yat-sen University (SYSU-PAFA), a 200 MHz drift tube linac (DTL), operating under continuous wave (CW) mode, has been designed. PAFA-DTL is expected to accelerate a 10 mA proton beam from 2.5 MeV to 8 MeV. Using the alternative phase focusing (APF) beam dynamics scheme, a compact cell array has been designed and optimized in order to limit the cavity length to 2.4 m with high acceleration efficiency. As a result, PAFA-DTL contains 31 acceleration cells with beam transmission efficiency reaches 100%, and better output beam quality is obtained by optimizing the input beam parameters. Interdigital H-mode (IH) structure is utilized in the PAFA-DTL cavity, which has achieved a high unloaded quality factor of 13987. Additionally, to ensure the stability of PAFA-DTL under CW operation, a low Kilpatrick factor (Kp) of 1.42 is obtained by adjusting the blending radius of the drift tubes (DTs) to reduce the risk of RF breakdown. The gap voltage distribution through RF design is compared with that from the beam dynamics, and the maximum absolute value of deviation is only 0.73%. In this paper, the detailed design and results of PAFA-DTL, including beam dynamics and RF design, are presented.