Electromagnetic design and analysis of pi-mode structure for CSNS

The phase one project of the China Spallation Neutron Source (CSNS) is in the stage of beam commissioning. In the future, the pi-mode structure (PIMS) will be used to upgrade the energy of linac from 80 MeV to 300 MeV. Some preliminarily study was done. The dimension of the PIMS was designed with 2D code SUPERFISH, where the operating frequency was 324 MHz and the β value was 0.4. Coupling coefficient, number of coupling slots and the shape of them were optimized by 3D code CST Microwave studio. The coupling coefficient was chosen to be 6.53%. Field flatness was tuned to 2.18% with slug tuners, which meet the operational requirements.