MAGNETIC SUBSTRATES REDUCE PERFORMANCE OF Y-Ba-Cu-O COATED SUPERCONDUCTORS.

Measurements by NIST scientists on Y-Ba-Cu-O coated superconductor tapes revealed that the use of magnetic substrates may reduce the current carrying capacity of the tapes when they are arranged in stacks of two or more layers. This finding has a significant bearing on the potential use of coated superconductors with magnetic substrates, particularly in low-field applications such as transmission lines. The disclosure of NIST's findings resulted in an accelerated effort at the Department of Energy's national labs and their industrial partners to develop non-magnetic substrates for coatedconductor fabrication.

High temperature superconducting tapes based upon coatings of Y-Ba-Cu-O on textured, buffered, magnetic nickel substrates showed a 15 % degradation in criticalcurrent density when the Y-Ba-Cu-O layer was sandwiched between two magnetic nickel substrates. This configuration commonly occurs in many applications where the conductor needs to be cabled or wound, such as in transmission lines and magnets. The interaction of the top and bottom nickel layers increases the perpendicular component of magnetic flux at the superconductor tape edges. This reduces the current carrying capacity of the superconductor due to the presence of the magnetic field. Removing the top nickel substrate restores the critical current density to its original value.