Analysis of Quench Initiation in YBCO Coated Conductors Using Optical Interferometric Techniques

Quench initiation in homogeneous YBa₂Cu₃O_7-delta (YBCO) coated conductors in nitrogen vapor has been analyzed using digital speckle pattern interferometry (DSPI) and measurements of the temporal evolution of the electric field along the conductor. These optical experiments can detect sample surface displacements smaller than 100 nm in the perpendicular direction. In these quench experiments, displacements are caused by dilatation effects associated with heat generation during the transition to the normal state. DSPI detects a multispot origin of quench initiation in these homogeneous materials. This confirms that, in addition to I _c distributions, there are other factors as inhomogeneities in thermal stabilizations that strongly determine sample quench behavior. The knowledge of the origin of this behavior is important for the design of different applications. The technique has been improved in order to characterize samples immersed in liquid nitrogen. The first results in 0.025 mm-thick Cu foils immersed in liquid nitrogen are presented. In addition to sample heating, DSPI allows the visualization of liquid nitrogen convention movements.