| The China Fusion Engineering Test Reactor(CFETR)project for the latest generation of large-scale scientific installations have been already in the future plans.The parameters of the fusion device will be greatly improved.For example,the maximum magnetic field of the CFETR CS magnet will exceed 15 T,which poses a huge challenge to superconducting technology.Compared with practical low-temperature superconducting materials such as NbTi and Nb3Sn,high-temperature superconducting materials Bi-2212 still has a very high upper critical field and excellent high-field current-carrying capacity,and is one of the most promising superconductors at high-field applications in the future.In particular,the critical performance of the Bi-2212 superconducting material can be significantly improved through the high-pressure heat treatment process,so its application range can be greatly expanded.In this paper,the Bi-2212 superconducting wire developed by the Northwest Institute of Nonferrous Metals(NIN)in China is used as the experimental subject.Its basic electromagnetic and mechanical properties are systematically tested and characterized,and the critical performance calibration parameters are obtained.A test device for studying the quench propagation characteristics of superconducting materials under variable temperature and variable field environments has been built.A one-dimensional quench propagation model has been established,and the minimum quench energy and quench propagation velocity of superconducting materials were measured,and discussed the results of measurement and simulation.At the same time,in order to verify the uniform performance of the Bi-2212 long wire,the Bi-2212 insert coil was designed and manufacture.The key process of the coil was explored,and the high-field performance test was successfully carried out.In this paper,we conducted a preliminary experimental study of Bi-2212 high-pressure heat treatment,then the critical characteristics and stress-strain performance of Bi-2212 superconducting wire under different temperatures and magnetic fields are studied.Including the relationship between the critical current with the temperature and magnetic field under different high-pressure heat treatment,the experimental data is fitted and analyzed through the Luca calibration model,a good comparability is obtained;then the experimental study of the relationship between the stress and strain of the Bi-2212 wire under the heat treatment of 3 MPa and without heat treatment.The results expressed the mechanical character of the superconducting wire will be better after the heat treatment;and relationship between the critical current and the strain of the sample under the heat treatment of 3 MPa and 5 MPa is also measured,it is found that the under higher heat treatment pressure,the critical performance of Bi-2212 superconducting material decreases with strain sensitivity,which is related to the density of the material under different heat treatment pressures.At the end,two alloy spring are compared.Compared with the Ti-6A1-4V alloy spring,the Be-Cu spring have similar thermal expansion coefficient with Bi-2212 can effectively eliminate the influence of initial strain,and the relationship between intrinsic strain and critical current can be directly obtained.This paper also.By testing the critical performance of Bi-2212 under different heat treatment pressures and the length of the effective heat treatment zone,and continuously optimizing the heat treatment curve,the optimal heat treatment process of 3 MPa was determined.On the other hand,we developed a test device that can study the normal propagation characteristics of superconducting materials under variable temperature and variable field environments.Then we carried out preliminary normal characteristics research,including MQE and NPVZ testing and analysis.We also established the one-dimensional propagation model about Bi-2212 superconducting wire,and compare with the model fitting data.Finally,this paper also designed and manufactured the Bi-2212 insert coil,including the electromagnetic structure design and manufacturing process of the coil,and successfully tested under the background magnetic field.The coil could achieve the critical current of 300 A and 130 A under the background field of 0 T and 12 T,respectively.Based on the experimental data,the performance of the Bi-2212 insert coil in the high-field(12 T),winding manufacturing process and the uniform property of the Bi-2212 long wire were successfully verified. |
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