We develop and manufacture high temperature superconductor Roebel cable for use in high field and accelerator magnets, transformers, generators and motors.
The benefits of Roebel cable
Superconductivity applications that require a current capacity of thousands of amps necessitate the use of a cable rather than a wire.
The best cable is designed so that every strand is electromagnetically and mechanically equivalent. High temperature superconducting (HTS) Roebel cables are the only way to achieve this with HTS conductors. They are also ideally suited for coil and magnet winding.
Commercial cable productions
We formed GCS Ltd in 2007 through a commercial partnership with General Cable Corporation to manufacture HTS Roebel cable. GCS Ltd supplies HTS Roebel cable to leading institutions and corporations around the world.
Wire must be of high uniformity across its width to be suitable for Roebel manufacture. Once we have verified that the current carrying properties are unaffected by our punching process, we can use wire from any manufacturer.
The wire is first cut in a reel-to-reel punching machine to form the serpentine strands of cable shown below.
Once the strand has been formed, it is assembled into a cable by a winding machine.
Roebel cable for transformers
In 2013 and 2014 we built a 1 MVA distribution level transformer using HTS Roebel cable for the secondary winding. The solenoid winding used a 20 m 15/5 cable with an operating current up to approximately 2000 A at –203°C.
Measurements of AC loss in the winding showed that the Roebel cable reduces losses to a level where they are less than or comparable to other losses in the system, such as current lead and cryostat losses.
The project showed that Roebel cable is stable in operation and a suitable conductor for HTS transformers.
HTS Roebel for accelerator magnets
Roebel cables are a good candidate conductor for the next generation of accelerator magnets. These may be used in a Future Circular Collider as well as upgrades to the existing Large Hadron Collider. Roebel cable based on YBCO type material has the ability to operate at higher fields than the low temperature NbTi and Nb3Sn superconductors that are currently used.
The main research tasks are to ensure that Roebel cables can meet the mechanical requirements for accelerator magnets—the mechanical forces are large and the cable needs to be supported by an impregnation to ensure its mechanical integrity. There are also challenges in making sure that cable strands are evenly spaced and do not move during coil formation and cause damage.
HTS Roebel cables for ultra-high field magnets
Very high field magnets are used in the frontiers of physics and materials research. One example is the 45 T hybrid magnet, housed at the National High Magnetic Field Laboratory in Tallahassee, Florida.
Because high temperature conductors can continue to carry high current densities even up to 100 T, we are designing Roebel cable-based conductors that will enable planned new hybrid magnets to operate at up to 60 T. To withstand the very high stresses within these magnets, the conductor must be placed inside a mechanically strong conduit (usually made of stainless steel or Hastelloy) to form a cable-in-conduit conductor (CICC).
We are currently building the first CICC Roebel conductors and testing their mechanical properties. Unlike previous CICC made from low temperature superconductors, Roebel cable cannot be mechanically compressed by the conduit.
Other research is investigating how the cable can be made mechanically robust and meet the electromagnetic requirements, such as stability, while ramping the current as required in these applications.
View our recent publications about Roebel cable.