AC Loss And Dynamic Stability Analysis Of High Temperature Superconducting Magnets

The thermal stability of high temperature superconducting magnet is an important part of the safety assessment,the electromagnetic characteristics of high temperature superconductor which are highly relevant to its temperature,transported current and magnetic field vector show obvious nonlinear features.Therefore,the stability analysis of high temperature superconducting magnets is extremely complicated,and many factors such as cooling condition,current,magnetic field,and temperature should be evaluated.The paper studies the directly coupled method of electromagnetic model and thermal model,the modelling of common structures of HTS magnets are analyzed in this paper,we also propose a quench model under constant current situation based on the extended critical current density and verified the validity of the model.In this paper,two different evaluation metrics are used to measure the dynamic stability of HTS coil during quench process,and the method to improve the stability of HTS magnet is analyzed.The specific contents are as follows:(1)Solenoid coils and racetrack coils are analyzed in this paper.On the basis of E-J exponent model,a 2D axisymmetric FEM model and 3D FEM model are established,which laid the foundation of assessing the stability of HTS magnet and the quench model.(2)Based on the voltage current characteristic of the HTS tape itself,the electrical conductivity of the superconducting tape is redefined in this paper,the concept of the expansion of the critical current density is first proposed to solve the singularity of J_c(B,T)which otherwise will lead the calculation not converge.The essence of the definition is the extended description of the HTS tape conductivity under normal state.Based on the extended critical current density,a quench model under constant current is proposed.The experimental results are consistent with the calculated results of 2D axisymmetric quench model under constant current,which validates the effectiveness of the axisymmetric quench model.(3)Based on the LabVIEW platform,this paper design and build the HTS coil testing subsystem of the WHMFC aims at the quench study of HTS coils.The system integrates different kinds of technologies of platform,and effectively solves all kinds of difficulties such as storage standardization of data and test signal,waveform parameterization and modular design of measurement.Thus data can be automatically collected,processed and analyzed,furthermore,the expansibility of the follow-up system development is enhanced with sufficient interfaces remained.(4)Based on the HTS coil test system,the related technologies for improving the electromagnetic thermal stability of HTS magnet are studied.The paper analyses the basic characteristics of the non-insulation HTS magnet.The thermal stability of HTS magnet under constant current condition can be improved by the non-insulation magnet.