Heat Treatment Optimization Studies on PIT Nb₃Sn Strand for the NED Project

T. Boutboul, L. Oberli, A. den Ouden, D. Pedrini, B. Seeber and G. Volpini

Abstract— For the Next European Dipole (NED) program, a Powder-In-Tube (PIT) strand was successfully developed by SMI. This high-performance Nb₃Sn strand presents a non-copper critical current density of ~ 2500 A/mm² at 12 T applied field and 4.2 K and a filament diameter around 50 µm. Extensive heat treatment optimization studies were performed in order to maximize both critical current and RRR, with a plateau temperature down to 625 ^oC and duration up to 400 hours. It appears that a critical current enhancement of ~ 10 % can be achieved for a reaction schedule of 320 hours at 625 ^oC with non-copper critical current density respectively exceeding 2700 and 1500 A/mm² at 12 and 15 T (4.2 K). Thanks to this modified heat treatment, this strand completely fulfills the NED stringent specification.

Index Terms—Niobium compounds, superconducting wires, low-temperature superconductors, superconducting materials measurements.

Manuscript received August 18, 2008. This work was supported in part by the European Community-Research Infrastructure Activity under the FP6 “Structuring the European Research Area” program (CARE, contract number RII3-CT-2003-506395)
T. Boutboul and L. Oberli are with CERN, AT department, CH-1211 Geneva 23, Switzerland (corresponding author: phone: +41-22-7679588; fax: +41-22-7676300; e-mail: thierry.boutboul@cern.ch).
A. den Ouden is with University of Twente, Faculty of Science and Technology, P.O. Box 217, 7500 AE Enschede, the Netherlands (e-mail: A.denOuden@tnw.utwente.nl).
D. Pedrini and G. Volpini are with INFN-Milan/LASA, via Fratelli Cervi 201, 20090 Segrate (Milan), Italy (e-mails: danilo.pedrini@mi.infn.it, giovanni.volpini@mi.infn.it).
B. Seeber is with University of Geneva, 20 rue de l’Ecole de Médecine, CH-1211 Geneva, Switzerland (e-mail: Bernd.Seeber@physics.unige.ch).

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