Relationships Between Conductor Damage, Quenching and Electromechanical Behavior in YBCO Coated Conductors

The implementation of emerging superconducting materials into magnet systems with long service lifetimes requires a thorough understanding of their engineering properties, including their quench and electromechanical behaviors. Furthermore, it is essential to understand the role of defects in the conductor, whether they be pre-existing defects from the conductor manufacturing process that locally reduce J_c, or local defects that result from a non-destructive quench (i.e., a quench that may reduce J_c locally but does not significantly affect the end-to-end behavior). This paper reports results on both of these types of defects and the interplay between quenching and electromechanical behavior. Quench studies investigate the initiation and propagation of quenches in coated conductors. Disturbances in homogeneous conductors are initiated by a pulsed heater attached to the conductor. Disturbances in locally damaged conductors are initiated by increasing the transport current above the I_c at the local defect but below the end-to-end I_c. Samples are quenched to determine the minimum quench energy and the quench propagation velocity. Homogeneous samples are also quenched to the point of initiating local damage, thereby identifying the maximum allowable hot-spot temperature or hot-spot temperature gradient. Samples used in quench studies are subsequently used in I_c-strain measurements to determine how quenching affects subsequent performance. Samples that exhibit reduced I_c from quenching, and samples from regions adjacent to such damaged samples, are studied. It is found that quenching can reduce the electromechanical performance of conductors that do not initially show a reduction in their electrical performance.