| Currently,the International Thermal-Nuclear Experimental Reactor(ITER)has entered the construction phase and its first plasma would be in 2025.Based on ITER's technology,various countries have proposed research plans to build a fusion demonstration reactor(DEMO).China is also put forward its own "Chinese Fusion Engineering Test Reactor(CFETR)" project,its physical and engineering parameters between ITER and DEMO,the main target is the absorption of ITER's technology,and to develop the significant technologies for the future fusion power plant.Superconducting magnet is the core system of the tokamak,the fusion power is proportional to the magnetic field intensity of 4 power(?B4).By increasing the strength of magnetic field,the plasma constraint performance and stability can be improved.It can effectively reduce the size and costs of fusion power plant and make it more efficient.At present,ITER has the highest magnetic field among the superconducting tokamaks which are existing and under construction in the world.The central field of toroidal field is 5.3 T,and the maximum field on the TF coil reaches 11.8 T.The transient field of CS coils is up to the 13 T during operation.Which is close to the upper critical field of Nb3Sn superconductor at operating temperature.So it is necessary to find new kinds of superconducting material with higher performance to that can improve the performance of fusion reactor in the future.In the copper oxide superconductors,Bi-2212 round wire shows good performance at high magnetic field,relatively lower AC loss,and isotropous to the magnetic field.Its most advantage for fusion magnet is that Bi-2212 can be made into round wire,and easy for cabling.From the above,it can be seen that Bi-2212 is competitive in future fusion magnet,especially for central solenoid coils.In this thesis,the performances,cable structure and thermal stability of cable-in-conduit conductor of an Ag matrix Bi-2212 round wire developed in China are studied.First,the critical performances at various temperature and magnetic field of Bi-2212 wire are measured.Base on the experimental result and flux pinning theory,a critical surface model Jc(B,T)is established,which can describe the relationship among critical current and magnetic field and temperature of Bi-2212 wire well.The magnetization curves of Bi-2212 wire are measured at various conditions,and the hysteresis losses are calculated.A test facility was developed which can be applied in strain dependence critical current measurement for short sample of superconducting strands or tapes.Based on this facility,the impact of strain on the critical performance of Bi-2212 wire was studied.And according to the test results,the reversibility of strain dependence critical currentand its mechanism in different strain range were studied and discussed.The quench model at adiabatic condition of Bi-2212 wire was established,analytical method and numerical method were used to resolve the problem.In the numerical method,the implicit differential scheme was used to improve the accuracy of the solution.The minimum quench energy and quench velocity of Bi-2212 wire were calculated at different conditions by solving the model.In Bi-2212 cable-in-conduit conductor preliminary study.a sub-scale 3rd stage Bi-2212 cable was fabricated and tested to verify the feasibility of the short twist pitch cable structure to Bi-2212 conductor.And the impact of the depth of indentation on the wire,which could be caused during cabling,was also studied,as a reference for the analysis of the conductor performance degradation.Finally,the thermal stability of Bi-2212 cable-in-conduit conductor was analyzed.the influence of the heat treatment of Bi-2212 conductor to the conductor pressure drop was studied and analyzed.then the Bi-2212 wire was assumed to be used into the ITER CS coils,and the energy margins at different operating conditions of ITER CS coil with the performance and the properties of Bi-2212 wire were calculated and compared with the Nb3Sn conductor. |
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