The US Department of Energy (DOE) has awarded nGimat Co. a Small Business Innovation Research (SBIR) Phase II to develop insulation for superconducting Nb3Sn wire. This is expected to be a two-year contract with potential funding of approximately $750,000. The resulting wire will enable higher magnetic field strengths which can reduce required power and enhance system performance in applications such as higher resolution MRI scans for hospitals.
Nb3Sn superconducting wire is a preferred superconducting medium for many applications since it can produce a higher field than another common superconductor, NbTi, which is important in higher magnetic field applications such as superconducting undulators. However, Nb3Sn wire requires a "Wind & React" technique, and because the reacted wire is too brittle to wind, the wire is first wound around a yoke, then reacted at temperatures well in excess of 600 ºC in an inert environment. The wire must be insulated before winding, so the insulation must also be heated and remain intact throughout the wire's reaction. Insulation sheaths are currently available, most notably of fiberglass, but these relatively thick sheaths take up valuable space that could be occupied by superconductor, and their possible looseness around the wire makes uniform, well-packed winding difficult. To effectively incorporate Nb3Sn superconducting wire for desired high peak fields, a thinner insulation material (about 25 mm) at similar or even lower cost is desired.
The Phase II approach will build on the Phase I insulation developed as a thin, ceramic-based coating that can be wound and go through the wire's reaction cycle at >600 ºC in an inert environment. Use of a thin ceramic (<30 micron) allows insulation that adheres to the wire and forms a more stable and controllable base for precision winding compared to the typical fiberglass insulation, which often adds over 100 microns to the wire diameter. The Phase I coating unit will be improved to allow uniform coating deposition with minimal operator input onto production-scale, continuous lengths of wire that can then be wound on a short yoke and tested for superconductivity and other properties.
Applications for superconductors such as Nb3Sn require from less than ten kilometers of wire to more than 300 kilometers of wire, depending on specific use. The majority of the commercial superconductor market (>$4500M in 2004) is for magnetic resonance imaging (MRI) units. This segment, as well as R&D, on a global scale is expected to continue to dominate the market, while high growth rates are anticipated for industrial and electronic applications. Each of these markets represent significant opportunity for a thinner, economical insulation.