Studying Of The Electromagnetic And Mechanical Performance Of Superconducting Strands\Cables And Collider Magnets

Superconducting magnets have the advantages of low energy consumption,small size,light weight and have been widely used in clean energy,high-energy physics,transportation,medical equipment and other fields.Superconducting magnets are under extreme environments(extremely low temperature,high current and high magnetic field)and the structures of superconducting magnet need to stand the residual stress from the manufacture,thermal stress during cooling down and electromagnetic force during the operation.These stresses lead to the high stress and strain levels in the magnet structure.The strands which constitute the superconducting magnets are strain sensitive and may cause the coils and superconducting magnets performance degradation at the high strain level.High stress results in the magnet's structural damage.The influence of mechanical deformation on the transport performance of superconducting strands and the stress analysis of superconducting magnet become important factors affecting the application of strands and the superconducting magnets design and stable operation.These are also the hot topic in applied superconductivity research.Based on this,the electromagnetic and mechanical performance of superconducting strands\cables and collider magnets are studied.Firstly,the transport performance of Nb3 Sn superconducting strand under bending strain and the AC loss are studied.Based on the uniform continuum model of superconducting strands,the governing equation for the superconducting strand transporting is solved by finite element method.The fracture of the superconducting filament under large bending strain and the changing of solution domain and the boundary condition caused by the fracture are also considered.The results show that the electric field distribution on the cross-section of the strand is asymmetrically distributed under the bending strain.Under the large bending strain,the non-uniform distribution of the current on the cross-section of the strand is intensified,which results in the degradation of the strand transport performance.Then,considering the anisotropic resistivity of the superconducting wire region,a three-dimensional finite element model is put forward to calculate the AC loss of the twisted superconductor strand.The influence of the magnetic field/current amplitude and the twisted pitch of the superconducting wire on the AC loss of the strand under the complex loading condition are quantitatively studied.The influence of the direction of the magnetic field and the non-uniform distribution of the current on the cross-section of the strand on the AC loss is analyzed.It is found that the smaller the pitch of superconducting strand,the higher the AC loss under the transverse magnetic field.The larger the pitch of superconducting strand,the higher of the AC loss under the transporting AC current.The influence of transverse magnetic field on the AC loss is greater than that of axial magnetic field.Secondly,the effective modulus and bending mechanical behavior of Rutherford cable are studied.Based on superconducting filament level,this dissertation is to predict the effective modulus of Rutherford cable from the perspective of theoretical and finite element method.The effects of insulation thickness,the insulation and strand Young's modulus on effective modulus of Rutherford cable are discussed.It is found that the effective modulus of the cable is increased by increasing the insulation layer's and the strand's modulus.Increasing the thickness of insulation layer will reduce the transverse Young's modulus of the cable(including the Young's modulus of thickness direction and width direction).Then,the prominent and pop-out behavior of Rutherford cable(without considering epoxy resin and insulation layer)during the bending are studied based on the strands' trace analysis of the displacement in the width direction and the strain in the thickness.The influences of different bending radius,different tensile loads,different friction coefficients and different supporting conditions on Rutherford cable's prominent and pop-out behaviors are discussed.It is suggested that the support structure should be added to reduce the prominent and choosing a smaller load or a larger bending radius can reduce the pop-out in the process of the cable winding.Finally,a two-dimensional finite element model of the collider magnet considering the stress distribution during the quenching process is established,considering the lack of stress analysis during the quench in the collider magnet design.Considering the electromagnetic force and the thermal stress due to the thermal mismatching of different magnet material during the quench,the pre-stress in the assembly process,the stress distributions characteristics in the coils of Block-coil and Cos-? magnet under the uniform and Coupling-Loss Induced Quench(CLIQ)protection system designed for European particle collider are analyzed.The results show the stresses in the coil will increase significantly after the quench and the mechanical analysis after the quench should be included in the structural mechanics analysis of the magnet during the collider magnet design.