Design and beam dynamics study of a multifunctional MEBT for CSNS

Abstract The China Spallation Neutron Source (CSNS) is an accelerator-based facility that has been operating at a stable beam power of 160 kW since March 2024, representing a significant 60% increase over its original design capacity. The ongoing upgrade project, termed CSNS-II, aims to further enhance the linac output energy to 300 MeV by integrating a superconducting accelerator and increasing the peak current to 50 mA. As part of this upgrade, a versatile Medium Energy Beam Transport (MEBT) system has been meticulously studied and redesigned to satisfy the stringent requirements for beam loss control. The MEBT system boasts several key functions and features, including beam chopping for optimizing beam structure, scrapers to confine and remove beam halo particles, as well as separation and removal of associated protons from H^-. This comprehensive approach enables effective beam transport management within the MEBT system and ensures the maintenance of beam quality throughout the subsequent acceleration process. Detailed studies on beam performance and error analysis in conjunction with the main linac, have been conducted and are presented in this article. Extensive multiparticle simulations have demonstrated that the multifunctional MEBT is crucial in preventing unacceptable beam loss in the main linac, underscoring its significance in facilitating the successful operation and performance optimization of the CSNS-II facility.