High Strength Silver Sheath for Bi2212/Ag Conductor

This proposal describes an innovative high strength silver alloy for making Bi2212/Ag round wire conductor. To generate magnetic fields greater than 20 T, a new high field superconductor such as Bi2212 is needed. However, Bi2212 is brittle ceramic that can be easily damaged, and its critical current is very strain sensitive. The Bi2212 compound is contained in a silver matrix that is chemically compatible with the Bi2212 ceramic. Silver provides very little mechanical support for the superconductor during either magnet fabrication or operation. High field magnets are subject to large stresses, which can exceed the yield strength of the silver matrix, causing degradation of the superconductor, and necessitating more expensive approaches for making high field amgnets. This proposal seeks to develop a high strength, high modulus silver alloy for manufacturing Bi2212 round wire multifilament conductor. The silver is strengthened by a fine dispersion of alumina particles that are chemically inert to Bi2212 and produce an alloy having high strength and stiffness even after high temperature processing. The increased strength and stiffness provided by the silver alloy results in greater resistance to mechanical stresses and electromagnetic forces. These attributes simplify magnet design, resulting in reduced costs with the added benefit of higher performance. Potential applications include particle accelerators and high field NMR magnets. Phase I demonstrated the feasibility of all the critical aspects of the technology: production of an silver/alumina composite, fabrication of tubes from the composite and a Bi2212 conductor using a silver/alumina composite tube. The Phase II plan includes research to further refine the basic alloy formulation, develop improved processing technology, advance the production technology for making tubes, and a full scale demonstration for making a Bi2212 production conductor. Commercial Applications and Other Benefits: A high field superconductor such as Bi2212 will find its primary application in accelerator magnets for high energy physics. The other major application for the technology is high field nuclear magnetic resonance systems for imaging complex organic compounds and biological materials.