Mechanical Treatments at Room Temperature of Nb3Sn Practical Wires:
Pre-torsion for Wires with a Different Architecture

P Badica ^1,2, H Oguro ¹, S Awaji ¹, G Nishijima ¹, K Watanabe ¹

(1) High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
(2) National Institute of Materials Physics, Bucharest-Magurele, POB MG-7, 077125, Romania
E-mail: badica2003@yahoo.com

Abstract - Room temperature mechanical treatment consisting of multiple torsion loadings (named pre-torsion) was applied to short samples of Nb3Sn composite wires with different architecture to reduce thermal residual compressive strain experienced by the superconducting Nb3Sn filaments. Due to this effect all investigated wires have shown enhancement of the critical current density, Ic up to 56% at 15T and 4.2K. Enhancement of Ic was larger for the reinforced wires than for the wires without reinforcement suggesting that reinforcement is useful in strain relaxation during pre-torsion. The best results were obtained when the position of the reinforcement was located in the outer region of the wire. Pre-torsion is similar or more efficient than cycles of bending loadings (named pre-bending). For pre-torsion, important parameter is the rotation angle per length of the wire and optimum conditions for short wires are valid for long wires. Nonuniformity of Ic along the length of a 0.99 m wire after pre-torsion was minimal, within uncertainty of Ic measurement.

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Received January 29, 2008; accepted March 3, 2008.  Reference No. ST32; Category 5.
Based on paper accepted for Proceedings of EUCAS 2007; published in JPCS 98 (2008), paper # 012036