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

Background A lowβsuperconducting elliptical cavity was designed for the China Spallation Neutron Source phase II project(CSNS-II).Methods The method to improve the mechanical stability of the lowβsuperconducting 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 k_(L)(LFD)and the helium pressure sensitivity factor k_(p)(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.Results 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,k_(L) and k_(p) 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.Conclusion The mechanical design of CSNS-II 648 MHz five-cell lowβsuperconducting 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.

Structural design of 648 MHz single spoke resonator prototype at CSNS

Purpose Superconducting radio frequency(SRF)cavities are adopted to upgrade the CSNS Linac energy from 80 to 300 MeV in phaseⅡ.A 648 MHz single spoke resonator(SSR)prototype has a compact size and low cost,which is a good pre-research cavity for CSNS to learn SRF technology.In this paper,the sequential approach of analysis and optimization performed for the structural design of 648 MHz SSR prototype are presented.Methods The COMSOL Multiphysics is used to perform the multiphysics analysis of jacketed cavity.Firstly,the mechanical performance of bare cavity is estimated,and then,several stiffeners are added to strengthen the cavity.After that,the Lorentz coefficient and helium fluctuation df/dp of jacketed cavity are optimized.At last,the tuning sensitivity and mechanical performance of maximum allowable working pressure are calculated.Results The final results of Lorentz coefficient and df/dp are-5.06 Hz/(MV/m)^(2)and 0.3 Hz/mbar,respectively,and the tuning range of jacketed cavity is larger than±1000 kHz at 2 K.Conclusion The structural design of a 648 MHz SSR prototype is performed in this paper.The Lorentz coefficient and df/dp are carefully optimized.The simulation result shows all mechanical performance satisfies the design goals very well.

RF design of a compact 648 MHz single spoke cavity at CSNS

Purpose In order to increase CSNS beam power from 100 to 500 kW,the linac injection energy needs to be increased from 80 to 300 MeV.The combined layout of superconducting spoke cavities and lliptical cavities will be adopted to accelerate H-beam to 300 MeV.In this paper,a compact single spoke cavity withφ50-mm beam aperture was proposed,with the RF performance of the spoke cavity optimized to E_(p)/E_(acc).<5,E_(p)/E_(acc)<9,as well as the good multipacting behavior.Methods CST Microwave Studio was used to optimize the RF performance(E_(peak)/E_(acc),B_(peak)/E_(acc) R/Q)with cavity geometry parameters.After electromagnetic design was finished,multipacting behavior was studied with CST Particle Studio module,and cavity shape modification was made to get a reasonable<SEY>value.Results The simulation got optimum results of E_(peak)/E_(acc)=4.97 and B_(peak)/E_((acc)=8.42 mT/(MV/m),and the<SEY>max is 1.52at E_(acc)=7.74 MV/m.Conclusion A 648 MHzβ=0.4 single spoke cavity with beam apertureФ50 mm was proposed in the paper.This compact cavity may be a very promising option for CSNS linac upgrading.In addition to the optimization of the RF parameters,the multipacting behavior of the cavity is also studied,and cavity shape is optimized to reduce<SEY>value.