The Department of Energy's High Temperature Superconducting (HTS) wire research has progressed from "First Generation" to "Second Generation" to fulfill its mission for higher-performance, lower cost wire at long lengths.

"First Generation" (1G) HTS wires were manufactured by traditional materials processing. This process is a technique that was discovered in the late 1980s and has been perfected to a high level of sophistication by several companies worldwide. It entails the packing of silver tubes with powders followed by several steps of heating, drawing, and rolling of the tubes to produce long wires with a stacked platelet structure in the superconductor. Silver is an excellent match to this process, as it does not react with the HTS materials and allows the oxygenation needed to form the superconducting phase during the heating process.

"Second Generation" (2G) HTS wires resulted primarily from mid-1990s discoveries at the Los Alamos National Laboratory (LANL) and the Oak Ridge National Laboratory (ORNL). The methodology utilizes the phenomenon of "epitaxial" growth, where films deposited on a prepared structure can assume the substrate's crystal orientation. These methods include rolling-assisted biaxially textured substrates (ORNL) and ion-beam-assisted deposition substrate texturing (LANL). While 1G manufacturing focused on perfecting a single process, the 2G experimental "space" is essentially unbounded, with the principal areas of focus being preparation of the substrate; deposition of film layers that will provide the desired match to the HTS crystal structure while not reacting with the HTS material; and deposition of the HTS materials on this template. The main advantages of 2G compared with 1G are the potentially lower cost and higher performance in magnetic fields characteristic of power technologies.

Performance in long wire lengths is quite close to that achievable in short lengths — such long-length uniformity is required for HTS electric wires where the overall current is limited by the lowest current section. The DOE high temperature superconductivity program is leading the world in critical current performance and long length wire.

HTS Wire Performance Metrics and Goals

The Department of Energy leads the Nation's research and development of HTS wire in power applications. The DOE HTS applications activities focus on the research, development, and testing of prototype HTS power system applications through industry-led projects. Research teams investigate adaptability issues for using superconducting wire in power system applications, which include transmission and distribution cables, fault-current limiters, and other applications. Application issues include the development of efficient cryogenic systems (PDF 108 KB), cable-winding techniques, and magnetic field research.

The applications activities at DOE have undergone a series of research and development phases since its inception in the mid-1990s. The program started with development of small-scale equipment that was heavily monitored in a laboratory setting. These initial attempts in building and operating HTS equipment facilitated more advanced systems that were used in industrial research settings in a less-controlled environment. Some examples of these projects included an HTS transformer, flywheel, magnetic separator, and novel cable project. Leveraging the lessons learned from these important demonstrations assisted in the development of several full-scale industrial cable projects. This phase has shifted the control to the industrial partners, which is a necessary step for demonstrating the transparency of HTS technologies.

The deployment of HTS technologies will help in not only increasing current carrying capacity on the electric grid, especially in urban areas, but also to relieve overburdened cables elsewhere in local grids, helping to ensure a continued delivery of safe and reliable power to all Americans.