| Chinese Fusion Engineering Testing Reactor(CFETR)will be built in China,which is to conduct the scientific research on stable and efficient fusion reactor.The central solenoid(CS)coil is one of the critical components of the CFETR magnet system.The project of the CFETR CS model coil is being carried out to develop and verify the key techniques and manufacturing processes of large-scale superconducting magnet,the highest field of the CS model coil is 12 T,and the largest magnetic field change rate is 1.5 T/s.the project is aiming to complete the manufacturing and performance evaluation of the model coil.Superconducting joint is one of the key technologies for manufacturing model coil,the main function of the joint is to be used to connect the adjacent windings electrically and hydraulically,the Joule heat and ac losses generated by the joints will add extra heat loads to the cryoplant.The main content of this paper is as follows.Firstly,according to the conductor parameters and magnet structure of CS model coil,the design requirements of the superconducting joint are determined,the structure design of the superconducting joint of CS model coil is carried out,and the structure form and related parameters are determined.On this basis,the important design parameters of the superconducting joint,including dc resistance and ac loss,are analyzed and estimated theoretically.It provides a theoretical basis for the design of the superconducting joint.Many technical research and development works have been launched for CSMC joint fabrication.It mainly includes:RRR test of copper,vacuum brazing terminal sleeve and NDE test,jacket removal,superconducting cable surface treatment(Ni removal and silver plating for NbTi cable,Cr removal for Nb3Sn cable),terminal sleeve compaction,Nb3Sn cable and terminal sleeve sintered,NbTi cable and terminal sleeve soldered and so on.Through the research on the joint technology for CS model coil,the feasible manufactring process of the joint is determined,which also lays a foundation for the development of the full-size joint sample.Thirdly,the development and test of NbTi CICC superconducting joint are carried out to verify the manufacturing process of the joint.The design of NbTi-NbTi full-size superconducting joint sample is carried out,and the manufacturing process of the sample is described in detail.A 24 kA superconducting transformer is designed to feed the joint sample,the hall sensor calibration and error analysis of the current measurement,and the dc resistance of the superconducting joint in different current is tested.The dc resistance test result of the superconducting joint is verified by the method of secondary loop current attenuation.The dc resistance of the NbTi-NbTi superconducting joint is about 0.5 n?,satisfies the design requirements of the CS model coil superconducting joint.Finally,prior to the joint fabrecation in field,the electrical performance of the prototype superconducting joint must be tested.Based on the test requirements and the background of the test device,the Nb3Sn-NbTi superconducting joint sample is designed.The manufacturing process of Nb3Sn terminal is introduced,and the soldering of the joint terminations is described in detail.The dc resistance of Nb3Sn-NbTi superconducting joint is about 1.5 n? in 5 T background field and 47.65 kA operation current,and meets the below 5 n? criterion.The ac loss of the joint is less than 30 J/cycle with the amplitude of 0.2 T and frequency in the range of 0.03-1 Hz,The peak of ac loss is in the 0.1 Hz.A linear summation model(LSM)and a multizone partial shielding model(MPAS)are used to analyze and simulate the ac loss test results.According to the test results,the joint ac loss power of CS model coil is calculated during ac waveform.The peak loss power of the Nb3Sn-NbTi joint is about 50 W.The maximum temperature rise of the joint is about 0.75 K and the temperature margin is about 2.15 K.The superconducting joints of the CSMC can operate steadily. |
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