Quench Detection of Bi2223/Ag Insulated Double-Pancake Coil Using Distributed Optic Fiber Sensor

Insulated high-temperature superconducting (HTS) magnet has extremely high upper critical field and excellent current carrying capacity, which serves as preferred option for China fusion engineering experimental reactor central solenoid magnet, the fusion device in the future. This paper makes the use of distributed optical fiber sensing sensor (DOFS) to study a propagation rule of hotspot temperature of HTS insulated double-pancake coil under different steady operating current by imposing thermal disturbance to local sections. Select two pieces of flexural flexible optic fibers with spatial resolution of 1 cm and sampling frequency of 1 Hz to detect the temperature of the insulated double-pancake coil, and proceed with quench propagation experiment under the condition of self-field and air cooling. The results show that the hotspot temperature propagates along the axial direction of the coil, and passes through the turn-to-turn insulation for radial propagation. It is discovered that as compared with quench voltage signal, variation to spectral offset of optic fiber is approximately 10 s earlier than the voltage signal, and is available for the positioning of hotspot. It is also verified that the DOFS can be used for a quench detection of the HTS insulated coil.