Experiment Investigation Of Magneto-mechanical Behaviors Of Low-Temperature Superconducting Magnets In A Complicated Environment

With the development of superconductive science and technology, more and more superconducting magnets are being used in large electromagnetic scientific instruments and equipments with features of large volume and high magnetic fields. On the view of superconducting magnet design, the more high magnetic field will be obtained as the carry-current inside the superconducting magnet increases. However, since critical states of superconductors (magnetic field, current, temperature) are limited, as high magnetic field is achieved, its ability of carry-current will reduce sharply. And with the increase of carry current and magnetic field, the effect of temperature and the costs of cooling at extremely low temperature will also rise substantially. How to find a kind of balancing and optimization in the restriction of multi-factor, which have become a key problem in its design and R&D. In addition, continued raising carry-current superconducting coils are also exposed to large Lorentz forces with leading to a series of challenge on design and security of superconducting magnet structure. And during the operation of superconducting magnet, the entire superconducting magnet structure must work in multi-field environment, which include mighty current-magnetic field and ultra-low temperature, and those complicated environmental field will be also interaction. Obviously, the consideration only related to the electromagnetic characteristics, simple environmental field and strength of structure in the design of the superconducting magnet is always inadequate. Therefore, the study of superconducting magnet considering magneto-mechanical performance under complicated environment is important.Based on the measurement and analysis of mechanical behavior in some SC magnets produced by IMP in recent years, this dissertation presents related strain measurement using low-temperature strain gauge and its compensation technology. At the same time, cryogenic temperature dependence of tensile response of NbTi/Cu superconducting composite wires and its pure filaments also were argued in detail.(1) Strain measurements and analysis on LPT model superconducting magnet (5T) during coil excitation. Firstly, the feasibility of low-temperature strain measurements is carried out. Using low-temperature strain gauge and wireless strain acquisition system, the strain measurement of a cantilevered beam soaked to liquid nitrogen under static load is introduced. Based on this strain measurement technology, the hoop and axial strains of the LPT model superconducting magnet (5T) under cryogenic temperature and intense magnetic field were also measured effectively. Secondly, considering magneto-mechanical coupled effect, the deformation of superconducting magnet under intense magnetic field is analyzed by means of nonlinear FEM. The experimental data and simulation predictions show good agreements.(2) Measurements of mechanics and electromagnetics of C-ADS injector II superconducting solenoid structure in multi-field environment. Appling cryogenics mechanical measurement and its compensatory technology, their strain measurements can effectively capture the mechanical behavior of the C-ADS injector II superconducting solenoid structures in multi-field environment (4.2K,8.2T). And based on the rapid change characteristic of strain detetion signal during quench test, the strain measurements can also warn and detect the quench response of superconducting magnet.(3) Based on the strain measurement at cryogenic temperature and under intense magnetic field, a new non-electric quench detection method of a superconducting solenoid magnet is presented. During the excitation, electromagnetic, temperature and strain signal were real-time measured and analyzed, and the quench detection method based on the strain measurements for spontaneous quench of low temperature superconducting magnet is put forward. Applying the method, based on a LPT superconducting solenoid model magnet (5T) and C-ADS injectorⅡ superconducting solenoid structure, the spontaneous quench of low temperature superconducting magnet were performed successfully. At the same time, based on time lags of strain-based quench detection for multiple points, the axial quench propagation velocity of the solenoid is evaluated. This result fall to the same order of magnitude as other evaluation methods for low-temperature superconducting magnet.(4) The cryogenic test system of mechanical properties of superconducting composites and related experimental study. The development of the cryogenic test system of the thermo-mechanical coupling performance of superconducting materials under cryogenic temperature is introduced. The effects of variable cryogenic temperature on the tensile response are reported for the commercial superconducting composite wires consisting of niobium-titanium filaments in a copper matrix (NbTi/Cu). The mechanical behavior of the NbTi/Cu composite wire and pure NbTi filaments, including the tensile strength and elongation at fracture, yield strength and Young’s modulus, are further captured. There shows that tensile strengths and Young’s moduli of NbTi/Cu composite wire and pure NbTi filaments are almost linearly dependent on the temperature, while the elongation at fracture and yield strength exhibit notable nonlinear features with the superconducting wires cooling. In addition, based on the mechanical properties measured from room temperature to liquid nitrogen temperature, these properties at lower temperature of4.2K are extrapolated for the NbTi/Cu composite wire and NbTi filaments, which are compared with the experiment data in the literature.