|Access My Subscription|
|Order Any Article|
|Premium Subscriber Content|
|Industry News Releases|
|What Is Superconductivity?|
|Superconductor Week Forums|
|Home||Subscribe/Renew||Why Subscribe?||About||Free Content||Help & F.A.Q.||Calendar||Contact Us|
The DOE has awarded nGimat Co. of Atlanta, GA a two-year, $750,000 Small Business Innovation Research (SBIR) Phase II to develop insulation for superconducting Nb3Sn wire. The project goal is to develop insulation that will enable the development of higher magnetic field strengths for Nb3Sn magnets produced by the wind and react method.
The relatively thick insulation sheaths currently available take up valuable space that could be occupied by superconductor, and the potential for the insulator’s 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 goal for the insulation developed under this project is to allow realization of Nb3Sn’s higher Jc potential, which is currently inhibited at least in part by the lower packing factor allowed by thick insulation,” commented Michelle Hendrick, Process Support Manager at nGimat. “A more tightly defined magnetic field enables smaller and lower power consuming MRI and other high field devices to be made. Higher fields are required for enhanced acceleration, confinement and control of high-energy material.
Multiple Performance Characteristics for Wind and React Insulation
Nb3Sn must be reacted at high temperatures as part of the manufacturing process. Because this reaction yields wire that brittle and difficult to manipulate, magnet manufacturers wind coils before reacting them. Insulation materials must be able to withstand this process, as well as the extreme physical stresses that come from magnet operation.
“Current fiberglass insulation sleeves move and compress during winding, making positioning less exact, which can cause larger field errors. An ideal insulation would provide sufficient electrical insulation and thermal conductivity, be durable, be thin, and not react with the underlying wire.”
Developing the optimal insulation for Nb3Sn wires involves several hurdles. Hendrick commented: “The insulation must be able to withstand the reaction cycle of the wire, including temperatures typically around 700ºC, the application process must not negatively affect the underlying wire by allowing oxidation of the copper surface or elemental diffusion into the wire, and the materials of the insulation should be electrically insulating but thermally conductive to help dissipate heat build up in areas.”
Manufacturability also Important
“The insulation must be essentially defect free so electrical shorts do not occur, it must be flexible so the wire can be wound around a core or yoke, and it must be durable so it can be handled and not abraded by the yoke surface or winding process.
As the final wound wire is potted in epoxy, the insulation must also be conducive to epoxy infiltration between windings and not negatively react with the epoxy.
nGimat stated that requirements for Nb3Sn wire range from less than ten kilometers of wire to more than 300 kilometers, depending on the application: “And since the lengths of wire needed for useful applications are measured in kilometers, whatever insulation process is used must be amenable to long, continuous lengths of wire.”
Coating Includes Nano-Ceramic Particles
nGimat utilizes a nanomaterial dip coating in the insulation application process. Hendrick commented: ”Dip coating is amenable to coat long lengths of wire at reasonable speeds (multiple meters per minute) with consideration of coating quality.” Hendrick said nGimat’s dip process builds on existing technology: “The insulation we have developed is of a proprietary composition; it is based on nano-ceramic particles, and the composition of these materials is chosen to allow electrical insulation but not reaction with the wire.
“The composition is designed to be flexible as applied but then goes through a transformation during the wire heating treatment that binds the nano-ceramic particles together, which leaves the coating less flexible. Since it is already wound in position, it does not need to move after heating.”
Nb3Sn Wire Source Not Decided
nGimat will use copper-clad Nb3Sn superconductor for all magnet testing, the copper being used as a surrogate due to cost and availability. Hendrick commented: “In order to optimize the coating composition, the wire is monitored for possible copper oxidation before or after heating.”
Hendrick stated that nGimat was unsure whether it would purchase wire or collaborate for the project. “nGimat is not involved with manufacturing superconducting wire. The insulation will be made available through nGimat applying the coating as needed and then via licensing or some other conduit that makes the most sense at various volumes.”
Nb3Sn Insulation Prices Range Widely
nGimat declined to comment on the costs involved in manufacturing insulation for Nb3Sn wire, saying only that it was a significant consideration. Hendrick stated that due to the current availability of Nb3Sn wire insulation, the driver for a thin alternative is improved performance of the final application: “Nonetheless, with insulation prices in 2008 ranging from $0.20 per meter of insulation to $20 per meter, our goal is to keep our costs within the lower end of this range.
“This should be feasible since the materials, process, and energy input to produce the insulation coating are not substantial. The labor required for the insulation process is also taken into account, and the equipment we use to apply the coatings is being designed so that only one person is necessary for setting up and monitoring the coating process.”
nGimat believes insulation techniques developed for Nb3Sn wire could be used for other superconducting cables: “The insulation is being developed for Nb3Sn wire that goes through the wind-and-react cycle, so it potentially will be useful for any application that requires such wire.”
nGimat Sees Broad Market Potential
Hendrick explained that low-Tc superconductors like Nb3Sn make up much of the commercial superconductor use. “Nb3Sn magnets have uses in high energy physics accelerators and magnetic fusion energy. Very high field NMR magnets are the largest commercial application. The initial market potential for this insulation will be national laboratories, and once verified by such entities the insulation will have potential use in commercial markets.
nGimat Believes Improved Insulation Key to Expansion of Nb3Sn Market
The majority of the commercial superconductor market, worth over $4.5 billion in 2004, is for MRI units. This segment, along with R&D, is widely expected to continue to dominate the global market, while many anticipatet high growth rates for industrial and electronic applications. nGimat believes each of these markets represent a significant opportunity for a thinner, economical insulation. Though only a small number of companies are working on developing Nb3Sn wire, nGimat said that the main obstacle in the development of many applications is the desire for insulation with improved properties.
nGimat stated that it was the only commercial company working on Nb3Sn wire insulation, and that “the most probable path of alternative insulation development is through a national laboratory where experts in this area test and verify insulation performance before commercial interest can be generated on a high level. Funding through the DOE SBIR program is a good conduit for small companies such as nGimat to develop a new technology in collaboration with a national lab, and then to generate interest in the commercial market through this collaboration.”
nGimat makes nanopowders for many different application areas, functional surfaces for applications like antimicrobial activity and self cleaning, coatings for electronic applications like embedded passives and sensors, and devices including phase shifters and tunable filters. The Company currently has a portfolio of 45 U.S. patents, 69 non-U.S. patents, and is processing about 60 patent applications. The company stated that it had 6 employees working part-time on developing Nb3Sn wire insulation.