Study On Multi-field Mechanical Problems Of Large Superconducting Magnet With Complex Structures During Assembly And Operation

The superconducting coil and magnet structure under the action of strong electromagnetic force.In addition to the superconducting material itself needs enough mechanical strength to overcome the ultra-high electromagnetic stress,the structural stability of superconducting magnet must be achieved by applying pre-stress or strong support and constraint.In addition,superconducting magnet is a complex multi-phase and multi-scale structure,including composite superconducting conductor with core wire or layered microstructure,paraffin or epoxy resin insulation material,support material and structure,etc.its design and preparation are often processed and assembled at room temperature,while the actual operating environment is at extremely low temperature(such as 4.2K),resulting in extreme strip The assembly mechanics problem under the component becomes a new challenge;the ultra-low temperature,high current and strong magnetic field of the operating environment make the superconducting magnet often in a complex and harsh stress environment,coupled with the characteristics of superconductivity degradation due to the strain sensitivity of superconducting materials,the related multi-field behavior and mechanical properties are directly related to the safe operation of the magnet structure.The mechanical problems in the design and development of high field superconducting magnets are recognized as the bottleneck problems in the application of superconducting magnets.Focusing on the assembly mechanics of typical composite structure of superconducting magnet,as well as the mechanical behavior analysis and test under multi-field environment,this paper carried out a systematic quantitative analysis and experimental research,developed new assembly technology,and successfully applied the relevant methods in the design and preparation of the fourth generation superconducting ECR ion source magnet(FECR)prototype in Institute of modern physics,Chinese Academy of Sciences(IMPCAS).The analysis is in good agreement with the measured data,which provides basic methods and theoretical guidance for the design and analysis of complex structure of large superconducting magnet and its operation test.(1)Focusing on the multi-field mechanical problems in the process of winding,cool down and excitation of superconducting solenoid,a typical structure of superconducting magnet,quantitative analysis and experimental research are carried out in this paper.The finite element models are established for the low temperature superconducting Nb₃Sn single solenoid magnet and Nb Ti combined superconducting solenoid magnet,respectively.The multi-field behavior analysis of the magnet in the process of cooling down and excitation is realized.The numerical prediction results are in good agreement with the experimental results,which verifies the reliability of the method.Furthermore,through optimization analysis and experimental verification,the assembly and mechanical analysis of the 5T split superconducting solenoid magnet are successfully solved based on the design and analysis of the cantilever type composite coil support structure.(2)In order to solve the assembly problem of Nb₃Sn complex superconducting magnet structure,a new assembly technology based on Bladder&key is developed.A water air hybrid pressurization system and a widened metal pressure capsule(Bladder)are developed.The reliability of the performance is verified by basic experiments.The numerical model of multi-field mechanical behavior for assembly and operation process is further developed,and the thermo-mechanical behavior analysis is carried out.By considering the influence of different Bladder operation pressure,interference and friction factor,the regulation mechanism of pre-stress on the internal mechanical characteristics of complex structure during assembly and operation process is revealed.At the same time,the strain in the process of structure assembly is measured and characterized by strain gauge and non-contact full field strain DIC(Digital Image Correlation)measurement.The analysis results are in good agreement with the measurement results.The relevant methods and results lay a solid foundation for the later coil structure assembly.(3)Combined with the development of the complex magnet structure of the fourth-generation superconducting ion source(including four solenoid coils and six sextupole coils),the combined support structure based on aluminum shell and the electro-mageto-thermo-mechanical multi-field analysis model based on ANSYS Workbench platform are developed.On this basis,the structural design and analysis of the magnet prototype are carried out,the complete assembly mechanics scheme of the magnet system is formed,and the quantitative results of each process are obtained.The results of numerical simulation can be used to determine the assembly parameters and evaluate the mechanical properties of the magnet prototype,which provides a theoretical basis and method support for the subsequent magnet development.(4)Considering the whole process of assembly,cool down and excitation,the simulation analysis of the assembly and loading process of the dummy coil structure of the superconducting ion source magnet prototype is carried out.At the same time,a complete assembly platform is built and the whole process of experimental test is carried out.The numerical prediction results are in good agreement with the experimental results,which provides effective theoretical and technical guidance for the assembly of the superconducting ion source magnet prototype.(5)The assembly of the superconducting coil and the shimming of the support structure of the magnet prototype of the superconducting ion source(FECR)were completed,and the experimental tests of the cool down and excitation process of the magnet prototype were carried out.The results show that:for the assembly and operation of the prototype,the test results are qualitatively consistent with the numerical prediction results,and the test results of the FECR magnet prototype achieve the expected goal,which verifies the effectiveness of the analysis method of the complex structure of superconducting magnet from the whole process of assembly,cool down and excitation operation Bladder&key assembly technology has theoretical and engineering significance for solving the assembly reliability of complex magnet structure of the fourth generation superconducting ion source,and for the development of large superconducting magnet in the future.