Mechanical Response And AC Loss In Superconductors Under Multi-physical Fields

High temperature superconducting materials have high critical transition temperature,critical current density and upper critical magnetic field,which are widely used in power,energy,medical,national defense and major scientific engineering fields.However,superconducting materials usually operate in extreme environments of extremely low temperature,high magnetic field,high current and complex mechanical loads.When superconducting materials operate under complex conditions,on the one hand,it is easy to cause structural deformation,performance degradation and even damage due to excessive electromagnetic force and thermal stress.On the other hand,the temperature rise caused by AC loss is prone to magnetic flux jump or even quench.Therefore,the study of the mechanical response and AC loss of HTS materials and structures in extreme environments is the basis for ensuring the safe and stable operation of superconducting magnets and equipment in multi-physical fields.In this paper,two-dimensional and three-dimensional numerical calculation models are established for bulk superconductors and cable structures which have been widely used in engineering applications.On the basis of considering the electric-magnetic-thermal coupling,the electromagnetic field and temperature distribution,AC loss and mechanical behavior of high-temperature superconducting structures are quantitatively studied in combination with relevant experimental results.The main research contents of this paper are as follows:Firstly,based on the H formulation and heat conduction equation,the magnetization behavior of inhomogeneous high-temperature superconductors under pulsed magnetic field is studied.The comparison with the experimental results shows that the calculated model can reproduce the variation of the trapped magnetic flux in the inhomogeneous bulk superconductor.The distributions of electromagnetic field and temperature without flux jump and with flux jump under the given coefficient of inhomogeneity is discussed,and the corresponding radial and hoop stress distributions are given.The most likely damage locations of the bulk superconductor under the two cases are obtained.The protection of the stainless steel ring reinforcement on the bulk is analyzed.Finally,the minimum pulse field amplitude with flux jump under different non-uniform coefficients is given.Secondly,the trapped field,temperature distribution and mechanical response of the bulk superconductors with finite length under pulsed field magnetization are studied.The influence of Lorentz force and thermal stress on the total stress in the process of pulsed field magnetization is discussed in detail.The difference between radial stress and hoop stress at different heights is analyzed.The effects of different metal ring reinforcement,pulse field amplitude,the diameter of bulk superconductors,the thickness of bulk superconductors and three multi-pulsed magnetization methods on the magnetization of the bulk are given.According to the excitation behavior of stacked bulks under pulsed field magnetization,the trapped field and stress under different stacking spacing,external magnetic field amplitude and critical current density are calculated.The magnetization law of stacked structure under field cooling and pulsed field magnetization is obtained by homogenization T-A formulation.Finally,based on the real geometry structure,the three-dimensional modeling of square stacked tapes,TSTC cable and CORC cable is carried out,and their trapped field characteristics,mechanical behavior and the influence of strain on AC loss are discussed.Based on the T-A formulation,the electromagnetic field distribution of stacked tapes in the field-cooled magnetization process is analyzed,and the mechanical response in the stacked structure is given combined with the electromagnetic force.After considering the strain distribution of superconducting layer in different cable structures during winding process,the AC loss characteristics of superconducting tapes under alternating current and alternating external magnetic field with different torsional pitch and winding pitch are analyzed by using strain-dependent critical current density.