Research On The Magnetic Field Stability Of No-Insulation High Temperature Superconducting Coil

In recent years,high temperature superconducting(HTS)insulated magnet has been widely concerned.Due to the low turn-to-turn transverse resistivity of no-insulation coil,the induced screening current is large and the coupling loss is high,which makes the central magnetic field of no-insulation coil drift for a long time.In order to solve the above problems,this paper analyzes the mechanism of the screening current of no-insulation coil,deduces the distribution of current density in the process of coil excitation,and then calculates the screening current and the screening current induced field.This thesis analyzes the methods to reduce the screening current,and proposes a method to reduce the screening current by enhancing the turn-to-turn transverse resistivity of no-insulation coil,so as to shorten the drift process of the central field of the coil,which is of great significance to promote the application of no-insulation superconducting coil.The key to reduce the screening current of the coil is to enhance the transverse resistivity of the coil.In this thesis,through physical and chemical methods,a compact high resistivity layer is formed on the outer surface of the turn-to-turn stainless steel tape,so as to enhance the overall transverse resistivity of the stainless steel(SS)tape.On the basis of keeping the minimum increase of stainless steel tape thickness and keeping the original properties of stainless steel tape,a variety of reinforcement processes were tested,analyzed and compared,and the treatment process was optimized.This thesis introduces the design and winding process of the no-insulation HTS double coil and the precautions in the winding process.The non-treated stainless steel tape and two kinds of optimized processes for enhancing the transverse resistivity of the stainless steel tape are used to co-wind the double coil with the HTS tape.At the same time,the length of coil tape is calculated,and the inductance of coil is deduced theoretically.Finally,the critical current of coil is simulated by COMSOL software.The PDE module based on H algorithm is simulated,and the simulation results are consistent with the experimental results,which has very important reference significance.Finally,the coil is tested in the liquid nitrogen environment.By changing the excitation rate,the drift process of the central magnetic field of every coil under different excitation rates is obtained.The experimental results of no-insulation HTS coil with enhanced transverse resistivity are faster to achieve stable magnetic field,and the stable value is larger than that of the non-treated one.The results are verified from the experimental point of view.It is proved that the enhancement of the transverse resistivity of the turn-to-turn stainless steel tape can effectively reduce the influence of the screening current induced field on the central magnetic field of the coil,shorten the drift process of the central field,and improve the temporal stability of the coil.The results of this paper lay a foundation for the application of no-insulation HTS magnet.