Superconducting Properties of a Prototype Pancake Coil using a MgB₂ Rutherford-type Stranded Conductor

Our group has developed a coil using MgB₂ wires for SMES. In this paper, a prototype coil using a MgB₂ Rutherford-type stranded conductor was fabricated based on react-and-wind (R&W) method. In the R&W method, a Rutherford-type conductor in which nine MgB₂ wires were wound at pitch of 450 mm around a copper former were manufactured using reacted wires (performed by Columbus Superconductors SpA), and then coiling was performed. The coil was cooled by conduction cooling and the I-V properties were evaluated under magnetic field. As a result, in the R&W method, critical current of a coil was degraded, since making a coil by hand would cause the strain beyond the scope of the assumption which was the marginally allowable bending strain. This result suggests the coil for SMES proposed in ASPCS is difficult to react before twisting, and Rutherford-type conductors should be fabricated before reacting, which means that coil processing should be performed based on the React after making stranded conductors and Wind method, or the wind-and-react method.