Influence of Pressure on the Critical Current and Levitation Properties of HTS Tapes

The contemporary composite high-temperature superconducting tapes (HTS tapes) are an advanced material for development of systems based on magnetic levitation. Development of levitation systems requires awareness on information on the effect of various external factors on levitation characteristics of the tapes. One of these factors is external mechanical pressure. For comprehension of the processes of deterioration of transport and levitation characteristics originating under mechanical loads on the stacks of composite HTS tapes, the effect of pressure on the critical current and levitation properties of the HTS tapes was investigated. The compression took place in the direction perpendicular to the plane of tape. The pressure varied from 0 Pa to 695 MPa, which corresponded to the force of impact of 10 kN on the stack of fragments of HTS tapes of 12 × 12 mm 2 . The measurements of critical current on applied pressure both for individual tapes and for the stacks of three and five tapes were carried out. Also, the investigation of effect of compression on the levitation force of the stack of 50 tapes was carried out. The theoretical model based on the finite element method implemented with use of the Comsol Multiphysics software package was developed to analyze the obtained experimental results. On the basis of the evidence found, it can be inferred that, at uniform compression of an individual tape and stacks of tapes with small thickness (up to five tapes), deterioration of characteristics of the HTS tape takes place mainly at the boundary of the area of influence, owing to existence of bending deformation. Deterioration of the critical current and levitation force of the HTS tapes under pressures to 695 MPa was not found outside the boundaries of the impact. However, at compression of large stacks of tapes (50 units), though a boundary of compression is absent, inhomogeneous deformation of the layers of the tape proceeds, which can be produced by local flexural deformations determined by fluctuations of both shape of the tapes and thickness of the layers in individual tapes. This is responsible for a linear decrease in the levitation force with increase in pressure.