The synchronous measurement of mechanical and magnetic characteristics of superconducting materials in extreme environments

Abstract

Thermomagnetic instability typically occurs before the quench of high temperature superconductors. Magnetic perturbation and thermal agitation are known to be the main driving force of thermomagnetic instability. However, the interaction between mechanical deformation and the thermomagnetic instability is still unclear. To investigate the phenomenon and inner principle of the thermomagnetic instability induced by mechanical deformation, an experimental method is proposed for the in-situ, real-time, and synchronous test of mechanical deformation and magnetic flux based on digital imaging correlation (DIC) and magneto-optical imaging (MOI). Under the current-carrying and external magnetic field conditions, uniaxial tensile tests of YBa₂Cu₃O_7-δ (YBCO) coated conductors (CCs) are carried out, in which the evolution and distribution magnetic flux induced by strain are studied. At the same time, chemical etching is adopted to explore the damage caused by mechanical deformation in YBCO layer. It is found through the experiment that the mechanical deformation can induce thermomagnetic instability, and threshold of strain for inducing flux motions is obtained. Meanwhile, magnetic flux avalanche occurs in front end of the flux penetration area in the case of current carrying. In addition, plenty of various-sizes transverse cracks are discovered in the superconducting layer whose distribution area basically coincides with the flux penetration area. The experiment results reveal the intrinsic correlation between the mechanical deformation and thermomagnetic instability of high temperature superconducting wires, which provides a direct experimental approach for the study of unpredicted quench behaviors of superconducting magnets.