| The China Accelerator Driven Sub-Critical System(CADS), promoted by Chinese Academy of Sciences in 2011, aims at the safe disposal of nuclear waste for the sustainable development of nuclear energy of China. CADS is based on a 1.5 Ge V, 10 m A CW superconducting(SC) linac as a driver, which can provide proton beam to bombard target to generate neutrons for a sub-critical reactor. The high energy section of the linac is composed of two families of SC elliptical cavities which are designed with geometrical beta 0.63 and 0.82. In this paper, the 650 MHz β=0.63 SC elliptical cavity is studied. A SC double-spoke cavity with the optimal β=0.67 for the mediumbeta accelerator of CADS is designed to compare with the elliptical cavity.The difficulty of the design of the SC elliptical cavity on the medium-beta section of a high-intensity accelerator is elaborated in the first part of this thesis. The design principle and process are introduced to optimize the elliptical cavity. The elliptical cavity is optimized for ideal electromagnetic and mechanical properties, which meets the requirement of CADS SC linac. The RF parameters of the elliptical cavity are better than those of other similar cavities in the world. Multipac 2.1 code was used to simulate the multipacting of the elliptical cavity. The result indicates that the multipacting barrier can be processed for a good cavity surface.HOMs not only impair the beam and degrade the beam quality but also interact with the cavity wall, inducing additional power dissipation and even thermal breakdown. The requirement of HOMs damping is calculated according to the beam intense and HOMs in the elliptical cavity simulated by CST. The frequency of HOMs is sufficiently far away from the machine resonance frequencyHelium tank is designed and optimized to ensure the mechanical stability of the elliptical cavity. Multi-discipline analysis based on the finite element method is used to analyze the detuning effects of the elliptical cavity. Generally, it includes the helium pressure coefficient, the Lorentz force detuning coefficient and microphone. The stiffening ring is optimized to improve the mechanical stability of the elliptical cavity and to reduce the detuning effects from these factors. |
