CSNS-Ⅱ超导椭球腔失谐研究  

Detuning Analysis of the Superconducting Elliptical Cavity for CSNS-Ⅱ Linac

作　　者：李波[1,2] 刘华昌 王云[1,2] 吴小磊 瞿培华[1,2] 李阿红 樊梦旭[1,2] 陈强 LI Bo;LIU Huachang;WANG Yun;WU Xiaolei;QU Peihua;LI Ahong;FAN Mengxu;CHEN Qiang(Institute of High Energy Physics,Chinese Academy of Science,Beijing 100049,China;Spallation Neutron Source science center,Dongguan 523803,Guangdong,China)

机构地区：[1]中国科学院高能物理研究所,北京100049 [2]散裂中子源科学中心,广东东莞523803

出　　处：《原子核物理评论》2020年第2期186-190,共5页Nuclear Physics Review

基　　金：广东省基础与应用基础研究基金联合基金资助项目(2019B1515120012)。

摘　　要：中国散裂中子源二期束流功率升级到500kW,直线加速器H^-的能量增益由现在的80MeV提高到300MeV以上,其中150~300MeV能量段采用648 MHzβ_g=0.60的5-cell超导椭球腔结构。超导椭球腔具有加速梯度高、结构简单、后处理容易等优点,缺点是结构强度弱、易失谐。本文主要研究该椭球腔的失谐特性。利用COMSOL Multiphysics软件进行了计算分析,在两端固定边界条件下,裸腔的氦压敏感性系数K_P=-45.705Hz/mbar(1mbar=100Pa),洛伦兹力失谐因子K_L=1.574Hz/(MV/m)^2。增加加强环并优化其位置来改善氦压敏感性系数和洛伦兹力失谐因子,通过计算分析最终确定选择双加强环方案来减小椭球腔的失谐。两个加强环位置分别取在75和120 mm的位置,腔体失谐的改善最大,K_P=6Hz/mbar,K_L=0.43Hz/(MV/m)^2。为了更准确地计算椭球腔的氦压敏感性系数和洛伦兹力失谐因子,本文引入调谐刚度边界条件进行失谐分析,在椭球腔调谐器端设置30kN/mm边界条件,另一端固定,计算得到氦压敏感性系数为4.8Hz/mbar,洛伦兹力失谐因子1.99Hz/(MV/m)^2,满足工程要求。另外,用CST软件对椭球腔的动态洛伦兹力失谐进行了初步分析,用软件Workbench计算了椭球腔的振动本征频率,结果显示,振动本征频率离射频脉冲重复频率及环境振动频率较远,不易发生共振失谐。China Spallation Neutron Source(CSNS)beam power will upgrade to 500 kW(CSNS-II),energy gain of H^-linac will up to 300 MeV from 80 MeV,and the 648 MHzβ_g=0.65-cell superconducting elliptical cavity will be adopted to accelerate the H^-from 150 to 300 MeV.Accompanied with the advantage of high accelerating gradient,simple structure,easy post-processing,weak stiffeness and detuning is the shortcoming of elliptical cavity,this study analysis detuning characteristic of the elliptical cavity.With code COMSOL Multiphysics,helium pressure sensitivity coefficient K_P and lorentz force detuning factor KL of bare cavity was calculated under two end fixed conditions,K_p=-45.705 Hz/mbar(1 mbar=100 Pa)and K_L=1.574 Hz/(MV/m)^2.Stiffener ring was designed and optimized to reduce the Helium pressure sensitivity coefficient and lorentz force detuning factor,and double ring was chosen to improve the detuning of elliptical cavity at last by vast calculation and analysis,the position of stiffener ring was optimized at 75 and 120 mm under two end fixed boundary,Helium pressure sensitivity coefficient drop down to K_P=6 Hz/mbar,lorentz force detuning factor drop down to K_L=0.43 Hz/(MV/m)^2.Moreover,elastic boundary was used to analyze helium pressure sensitivity coefficient and lorentz force detuning factor,more realistic results were got under tuner end 30 kN/mm boundary and the other end fixed condition,K_p=4.8 Hz/mbar and K_L=1.99 Hz/(MV/m)^2,meet engineering requirements.In addition,dynamic lorentz force detuning was analyzed qualitatively with code CST.And natural frequency of cavity was calculated by code Workbench,results show that nature frequency is far from RF pulse repetition rate and ambient vibration frequency,no resonance happen.

关 键 词：散裂中子源 超导椭球腔 氦压波动 洛伦兹力失谐 加强环 

分 类 号：TL53[核科学技术—核技术及应用]