Development Of Test Facility And Experimental Research On DC Performance Of High-Current Conductors

High-current superconducting conductors are widely used in fusion magnets and high energy accelerators.With the advancement of projects such as the China Fusion Engineering Test Reactor(CFETR)and the Circular Electron Positron Collider(CEPC),the performance of superconducting conductors in the future has been put forward with higher requirements.It's urgent to carry out experimental research on DC performance of new conductors.In this paper,a new test facility for DC performance measurement of straight conductors has been developed,whose maximum background magnetic field is 6 T with a maximum test current of 30 kA.The test technologies such as secondary current measurement,voltage tap technology,transverse stress applying and monitoring have been developed.Theoretical DC performance analysis of conductors are also carried out.The overall design of the conductor test facility is completed,including the determination of facility composition and parameters,the optimization of sample space,the determination of sample current range and power supply method.In order to ensure the safety of background magnet,quench detection and protection scheme is designed.The quench protection threshold and protection resistance are analyzed.In response to the problem of large heat leakage of current leads,a pair of 6 kA gas-cooled high-temperature superconducting current leads is independently developed.The heat leakage of a single lead is about 2.07 W.In terms of the optimization of the heat leakage of the gas-cooled high-temperature superconducting current leads,the proposed new solution form realizes the unity of the temperature distribution solutions of the microelements in the copper segment and the superconducting segment.The design of the new "CIC bundle" copper heat exchanger not only increases the heat exchange area,but also improves the convection heat transfer coefficient.In order to further reduce the heat leakage of the device,the Dewar structure and its heat transfer structure are optimized and analyzed.The overall heat leakage of the device after optimization is about 10.4 W.Development of superconducting transformer is carried out,including the optimization of transformer electromagnetic parameters,the design of transformer magnets,secondary windings,transformer terminals,the method of transformer fixing,and the test of transformer.Among them,the secondary winding design comprehensively considers the secondary current measurement,the force of transformer under background magnetic field and less secondary loop connector resistances.Aiming at the problem of torsion of transformer under background magnetic field,the optimization of position relationship between transformer and background magnet,the fixing structure design of transformer are carried out.Aiming at the problem that Hall sensor is susceptible to the stray fields during secondary current measurement,the "Hall sensors Pair" secondary current measurement method is developed to reduce the effect of stray fields.For the testing of armored conductors and cables,the passive sample support and the active sample support are developed respectively,and the assembly gap of the passive sample support are analyzed.The effects of cooling and electromagnetic force on transverse stress on the sample with active sample support are studied.At the same time,considering the stability margin of test conductor and the influence of transverse stress on performance of the sample,the selection basis of transverse stress at room temperature is summarized.Besides transverse stress applying technique,the technique of transverse stress monitoring is also studied.According to the transposition of superconducting wires in the cable,different voltage tap processing methods,"equipotential point" and "single wire monitoring",are given.The DC performance of NbTi Rutherford cable,MgB2 CICC(Cable-in-conduit Conductors)and YBCO CORC(Conductor on Round Core)are successfully measured.The influence of the change of induced voltage on the test results is analyzed,and measures to reduce this influence are proposed.The measurement errors of Ic(critical current)and joint resistance are also analyzed.In order to evaluate the conductor performance,considering the magnetic field distribution and equivalent strain on the cable,the conductor performance is compared with the performance of witness superconducting single wire.The "maximum magnetic field" and "average potential" evaluation methods are used to theoretically analyze the DC performance of high-current conductors.Taking the sample cable structure and voltage tap processing method into consideration,these two evaluation methods are compared.