Relaxation of Trapped High Magnetic Field in 100 m-long Class Solenoid Coil in Persistent Current Mode Operation

This paper reports on the relaxation of trapped magnetic field in a MgB₂ solenoid coil in PC mode operation. For PC mode operation, we fabricated a closed loop circuit with a MgB₂ coil, a PCS and some superconducting joints. The MgB₂ coil was fabricated employing a 100 m-long PIT processed MgB₂ wire using a wind & react method. The critical current I_c of the coil reached 166 A and the coil was able to generate a maximum magnetic field of about 2.5 T at 4.2 K without an external field. The PCS was fabricated employing a long NbTi wire stabilized Cu-Ni alloy. The joints were fabricated between MgB₂ and NbTi conductor, between NbTi (PCS) and NbTi conductor. The resistance of all fabricated joints was estimated to be less than 1.0times10^-13 Omega. In PC mode operation with the closed loop circuit, a magnetic field of 1.46 T was trapped for about 50000 s (above 12 hr.) without any detectable decay. These results demonstrate the possible use of the MgB ₂ superconductor for applications such as MRI superconducting magnet