The relaxation of a trapped magnetic field in a MgB2 solenoid coil, in persistent current (PC) mode operation, was reported. For the PC mode test, a closed-loop circuit was fabricated having a small MgB2 test coil, a persistent current switch and some superconducting joints. The MgB2 test coil was fabricated by using a wind-and-react method employing a 96m-long powder-in-tube processed MgB2 wire. The critical current of the coil reached 88A at 4.2K, without an external field. The resistance of the fabricated joints between the MgB2 and NbTi conductors (MgB2–NbTi) was estimated to be less than 1.0 x 10-13Ω. In PC mode with a closed-loop circuit, a magnetic field of 0.68T was trapped for more than 8h. These results demonstrated the possible use of MgB2 for applications in fields such as MRI and NMR.

Relaxation of a Trapped Magnetic Field in a 100m Long Class MgB2 Solenoid Coil in Persistent Current Mode Operation. M.Takahashi, K.Tanaka, M.Okada, H.Kitaguchi, H.Kumakura: Superconductor Science and Technology, 2005, 18, S373-5