Friday, 2D-12, 5:00-5:10

Angular Dependence of Critical Current in YBCO Coated Tapes

Jan Jaroszynski

Aixia Xu, Youri Viouchkov and David Larbalestier

National High Magnetic Field Laboratory, 1800 E.Paul Dirac Dr. Tallahassee, FL 32310, USA phone 1-850-6457490, fax 1-850-644 5038, e-mail jaroszy@magnet.fsu.edu

It is now well established that YBCO can incorporate many different types of pinning centers with significant effect on the critical current. However, the angular anisotropy of the critical current density and the microscopic mechanisms behind it are still poorly understood in emerging YBCO coated conductors (CC). Here we present detailed measurements of the critical current in different YBCO CC fabricated by Super Power Inc. The measurements were performed in magnetic fields up to 31 T on short samples (length ~ 2cm, width ~ 1mm) at 4.2K so as to be relevant for very high field magnet design. To make these measurements possible, we developed a high current (up to 500 A) rotator probe with angular resolution better than 1 degree. We studied tapes with dense nano-sized non-superconducting precipitates. Measurements performed in moderate magnetic fields showed nontrivial, and not fully understood, dependence of the critical current on field, temperature and angle. In particular, these pinning nanostructures strongly enhance critical current in the out-of -plane configuration with B||c, and thus diminish the current anisotropy well below the effective mass anisotropy. However, at fields greater than ~15 T these correlated pinning effects are washed out and the angular current anisotropy reaches a value of ~5. Importantly, a very sharp peak of the angular current dependence is observed around the in-plane configuration, with full-width half-maximum as small as ~14 degrees. Our results lead to a better understanding of the pinning mechanism in YBCO CC. Angular characterization of the critical density provides data to optimize the design of superconducting magnets made of YBCO CC and discriminate whether it is the parallel field critical current that limits the highest field possible in the magnet, or if it is limited by the field at the ends of the coil where the field vector is far from the plane of the CC.

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