Huang, Y.L. Chen, L. He, Y. Li, Y.M. Zhang, S.H. JACoW Geneva, Switzerland 978-3-95450-191-5 10.18429/JACoW-SRF2017-TUPB040 English 478-480 TUPB040 cavity ion HOM multipactoring linac Contribution to a conference proceedings 2018 2018-01 https://doi.org/10.18429/JACoW-SRF2017-TUPB040 http://jacow.org/srf2017/papers/tupb040.pdf Superconducting technology is adopted in the main accelerating section of the CW Linac in China Initiative Accelerator Driven System (CIADS) to accelerate the 10 mA proton beam from 2.1 MeV up to 1.5 GeV. The high energy section of the superconducting linac is composed of two families of SC elliptical cavities with optimum beta 0.62 and 0.82 for the acceleration of proton beam from 178 MeV to 1.5 GeV. In this paper, the design and optimization of the 650 MHz medium and high beta elliptical cavities are discussed, including the RF design, multipacting analysis, high order modes (HOMs) analysis, generator RF power calculation, and the mechanical design.