High-temperature superconducting (HTS) YBCO wire is a versatile technology for a number of military and commercial applications. However, anticipated military applications such as energy-dense electric propulsion systems (including motor and adjustable speed motor drives), directed-energy weapons (including the gyrotron magnet and power supply), and commercial applications such as motors, generators, transformers, and power transmission lines require improvement in the performance of such wires before these applications are broadly realized.

Lengths of 344 superconductors prepared with the 1.4-μm High-Temperature Superconducting layer were used to fabricate a solenoid coil. The coil was constructed from 12 pancake coils and used 420 meters of wire.
The objective of this work was to demonstrate the practical manufacturing of continuous lengths of 344 superconductor wire with a critical current exceeding 200 A (>500 A/cm-w) at 77K, self-field, using a low-cost, solution-based deposition process for the YBCO layer. The approach for the deposition of YBCO films is based on the ex situ conversion of a fluorine-based precursor deposited by a low-cost metal organic deposition (MOD) technique employed on a trifluoroacetate (TFA)-based precursor. For ex situ conversion of a thick MOD film, the challenge is threefold: 1) coating and decomposition of defect-free thick precursor film of sufficient thickness; 2) control of thick film epitaxial nucleation; and 3) control of through-thickness YBCO growth.

The project focused on developing a robust, multi-coat process and increasing the thickness of the single-coat process; characterization and optimization of the nucleation and growth stages of both the single- and multi-coat films; and transferring the thick-film coating-decomposition-reaction process to a long-length roll-to-roll manufacturing process.

A critical current of 560 A/cm-w was achieved in a 2-μm MOD film (660 A/cm-w was demonstrated in a 2-μm MOD film in a separately supported effort.). The maximum thickness of the single-coat MOD film was increased by 50% to 1.2 μm. The thick-film multi-coat and single-coat coating/decomposition processes were successfully demonstrated in a roll-to-roll manufacturing line. A thick-film conversion process for a 1.4-μm film was successfully demonstrated in a pilot roll-to-roll YBCO manufacturing furnace. Multiple 100-meter lengths of wire, with an Ic exceeding 300 A/cm-w, were fabricated in a pilot manufacturing line.

Key processing parameters were successfully developed and optimized for obtaining high critical currents in thick MOD-based YBCO films. The thick-film process also was successfully demonstrated in a roll-to-roll pilot manufacturing line. The 344 wires achieved end-to-end critical currents exceeding 300 A/cm-w (77K, self-field).

This work was done by Xiaoping Li of American Superconductor Corp. for the Air Force Office of Scientific Research. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Materials category. AFRL-0180

This Brief includes a Technical Support Package (TSP).
High Critical Current in Metal Organic Derived YBCO Films

(reference AFRL-0180) is currently available for download from the TSP library.

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This article first appeared in the February, 2011 issue of Defense Tech Briefs Magazine.

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