Mechanical design of a low β superconducting elliptical cavity for CSNS-II

A low β superconducting elliptical cavity was designed for the China Spallation Neutron Source phase II project (CSNS-II). The method to improve the mechanical stability of the low β superconducting elliptical cavity was introduced, and the corresponding mechanical design was given. The software COMSOL Multiphysics and ANSYS APDL were used to calculate the static Lorentz force detuning factor kL (LFD) and the helium pressure sensitivity factor kp (DFDP) of the bare cavity, which were − 4.71 Hz (MV/m)−2 and − 21.1 Hz/mbar, respectively. The double-ring stiffeners reinforcement scheme was adopted. The radii of the double-ring stiffeners were 70 and 135 mm, respectively. The structure design of the helium vessel of the cavity was given. The following is the mechanical parameters of the reinforced cavity, the tuning sensitivity is 199.8 kHz/mm, longitudinal stiffness is 4.76kN/mm, kL and kp were − 1.39 Hz (MV/m)−2 and 4.67 Hz/mbar, respectively, which met the operating requirements. The tuning sensitivity and stiffness of the reinforced cavity with different wall thicknesses were optimized, and the final wall thickness was selected as 4 mm. The mechanical design of CSNS-II 648 MHz five-cell low β superconducting elliptical cavity was introduced systematically in the paper. The LFD, DFDP, and the maximum surface stress of the cavity were reduced by optimizing the cavity wall thickness and the position of the double-ring stiffeners. The reinforced cavity met operational requirements.