First, some background
At the National MagLab, engineers are always trying to build stronger magnets, because stronger magnets mean more science discoveries. That generally means packing more current into a conductor so that it can generate a higher magnetic field. Magnets use different kinds of conductors, from copper, to low-temperature superconductors based on niobium, to high-temperature superconductors (HTS) such as barium-strontium-calcium copper oxide, also referred to as Bi2Sr2CaCu2O8, or Bi-2212.
What did researchers discover?
After tweaking the way they made the superconducting powder used to manufacture Bi-2212 wires, scientists and engineers saw a huge, 33 percent increase in the amount of current the wire could carry, also called its superconducting critical current density (or Jc). Measured at a temperature of 4.2 Kelvin and in a magnetic field of 15 teslas, the Jc increased from 4,200 to 5,600 amps per square millimeter.
Making the wire was a collaborative three-step process involving the National MagLab and industry partners: (1) synthesizing Bi-2212 powder (done by Georgia-based manufacturer nGimat); (2) fabricating a silver-sheathed wire (done by Bruker Oxford Superconductor Technology); and (3) heat treating the wire using overpressure processing to make it superconducting, a technique developed at the oxygen overpressure furnace facility at the MagLab's Applied Superconductivity Center.
Why is this important?
The next generation of all-superconducting magnets will generate fields well beyond the capability of existing niobium-based superconductors. This will require using coils made from materials such as Bi-2212, which is the only HTS material that can be fashioned into a round wire, which magnet designers and builders prefer over tape-shaped superconductors.
Who did the research?
J. Jiang1, E. Hellstrom1, D. Larbalestier1, M. White2, R. Nesbit2, Andrew Hunt2, Y. Huang3, H. Miao3
1Applied Superconductivity Center, National MagLab; 2nGimat; 3Bruker Oxford Superconductor Technology (BOST)
Why did this research need the MagLab?
The oxygen overpressure heat treatment was developed at the MagLab, and can only be performed here. The lab has installed several unique overpressure furnaces, which apply pressure to the Bi-2212 wire while it is being heat treated. The technique densifies the wire, increasing critical current density.
Details for scientists
- View or download the expert-level Science Highlight, New Bi-2212 (Bi2Sr2CaCu2O8) Powder Delivers Record Superconducting Critical Current Density in Bi-2212 Round Wire
This research was funded by the following grants: G.S. Boebinger (NSF DMR-1157490); D.C. Larbalestier (DOE-DE-SC00110421)
For more information, contact Eric Hellstrom.