Abstract
The flux jump in bulk superconductors is accompanied by a rapid change in temperature and magnetic field, which can induce change in electromagnetic bodyforce and thermal stress. It is well known that bulk superconductors are brittle and have low mechanical strength, and thus, large electromagnetic bodyforce and thermal stress can cause damage of the bulk superconductor. In this paper, an electromagnetic-thermal-mechanical multi-physics model is adopted to compute the mechanical response of a bulk superconductor during flux jump in an external magnetic field. The results indicate that the flux jump in the bulk superconductors can also lead to the jump of the average electromagnetic force, temperature, stress, and strain. Meanwhile, it can be found that the flux jump can occur more easily with a faster change in the magnetic field, a lower ambient temperature, and a large-size superconductor. The results also show that the peak value of thermal strain is much larger than the strain generated by electromagnetic bodyforce during the flux jump. In addition, the change in strain has the same trend as that of the temperature. Thus, the strain may also be used to monitor the flux jump.
Highlights
Melt-processed and largely grown high temperature bulk superconductors have significant potential in many engineering applications, such as rotating machines, magnetic bearings, and magnetic separation.1 Compared to permanent magnets, high temperature bulk superconductors can generate an order of magnitude higher magnetic field with the induced electrical current.2 Two conventional techniques, which include field-cooling magnetization (FC) and zero-field-cooling magnetization (ZFC), are used to magnetize high temperature bulk superconductors.3,4 The main difference is dependent on the sequence of cooling and external field loading
The temperature and electromagnetic field can both have a rapid change during the flux jump, which can generate large thermal stress and Lorentz force
This section discusses the effect of ramp rate of the external field, different ambient temperatures, and different radii on the flux jump
Summary
Melt-processed and largely grown high temperature bulk superconductors have significant potential in many engineering applications, such as rotating machines, magnetic bearings, and magnetic separation. Compared to permanent magnets, high temperature bulk superconductors can generate an order of magnitude higher magnetic field with the induced electrical current. Two conventional techniques, which include field-cooling magnetization (FC) and zero-field-cooling magnetization (ZFC), are used to magnetize high temperature bulk superconductors. The main difference is dependent on the sequence of cooling and external field loading. Based on the critical state model, a theory has been proposed to explain the flux jump of an infinite superconducting slab subjected to an external magnetic field.. The temperature and electromagnetic field can both have a rapid change during the flux jump, which can generate large thermal stress and Lorentz force. It is very important to clarify mechanical deformation of the bulk superconductor caused by electromagnetic force and thermal stress during the magnetization. The electromagnetic force and temperature are used to obtain the mechanical response of the MgB2 cylindrical bulk superconductor in the magnetic field. The stress generated during the flux jump is closely related to the ramp rate of the external field, ambient temperature, and radius of the bulk superconductor.
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