Huang, W.L. Liu, M.Y. Liu, Q.R. Liu, X.Y. Nie, X.J. Sui, Y.F. JACoW Publishing Geneva, Switzerland 2673-5350 978-3-95450-236-3 10.18429/JACoW-IBIC2023-TUP014 English 219-221 linac electron cavity proton neutron Contribution to a conference proceedings 2023 2023-12 https://doi.org/10.18429/JACoW-IBIC2023-TUP014 https://jacow.org/ibic2023/papers/tup014.pdf During the upgrade of linac in CSNS-II, the beam in-jection energy will increase from 80.1MeV to 300MeV and the beam power from 100kW to 500kW. A com-bined layout of superconducting spoke cavities and ellip-tical cavities is adopted to accelerate H⁻ beam to 300MeV. Due to a ~10ps short bunch width at the exit of the spoke SC section, the longitudinal beam density dis-tribution will be measured by bunch shape monitors using low energy secondary emission electrons. As the most important part of a bunch shape monitor, a prototype 324MHz RF deflector is designed and tuned on the basis of a quasi-symmetric λ/2 325MHz coaxial resona-tor, which was fabricated for the C-ADS proton accelera-tor project. Preliminary parameters of the bunch shape monitor are presented. Simulation of the RF deflector and test results in the laboratory are described and analysed.