周期载荷下Nb3Sn温度裕度及变形研究

Research on temperature margin and deformation for Nb3Sn with load cycle

国际热核聚变反应堆ITER和国内聚变工程实验堆CFETR装置上的CICC运行于复杂的电磁环境中,为应对12 T及更高电磁场的影响,其上的中心螺线和环向磁体已采用Nb3Sn超导材料,作为A15型的Nb3Sn材料对应变变化较敏感。而应变下温度裕度和变形等是影响低温(4.2/4.5 K)下超导体稳定运行的重要参数,为获得真实运行情况下磁场与电流产生的电动力所导致的周期应变对温度裕度等的作用,本文采用周期电磁载荷来模拟应变作用,利用温度裕度与刚度的数学计算方法,对Nb3Sn超导体的温度裕度和变形进行测试对比分析。结果显示分流温度和温度裕度随载荷周期增加而减小,其中分流温度在1~1000载荷周期快速变小,温度裕度在2000~3000载荷周期急剧减小;同时载荷周期导致股线刚度减小和股线变形增加。由此可见,载荷周期产生的应变导致Nb3Sn性能退化降级。

Conductors on ITER and CFETR will be operated in the complex electromagnetic environment.In response to impact of magnet field above 12 T,the Nb3Sn that is sensitive to strain changes as a15 type material has been applied to the central solenoid and the toroidal field on fusion device such as ITER and CFETR.The temperature margin and deformation under strain are important parameters affecting the stable operation of superconductors at low temperature(4.2/4.5 K).In order to obtain the periodic strain effect on temperature margin under real operation conditions caused by electric power from magnetic field and current,the periodic electromagnetic load was used to simulate the strain effect in this paper,and the temperature margin and deformation of Nb3Sn superconductor were measured and compared by using the mathematical calculation method.The results show that the current-sharing temperature and temperature margin decrease with the increase of load cycle,in which the current-sharing temperature decreases rapidly in 1~1000 load cycle and the temperature margin decreases sharply in 2000~3000 load cycle.At the same time,the load cycle leads to the decrease of strand stiffness and the increase of strand deformation.So,it is found that the performance degradation of Nb3Sn strand is resulted from strain caused by electromagnetic load cycle.