Measurement of Propagation Velocities of the Normal Zone in a 1 mφ×1 m Superconducting Solenoid Magnet

Propagation velocities of the normal zone in a 1 m×1 m superconducting solenoid magnet were unambiguously measured as a function of the magnet excitation current by inducing quenches with a heater. The magnet was built to study the feasibility of constructing thin, large solenoid magnets and it has a single layer aluminum-stabilized NbTi/Cu superconductor of 269 turns. The ratio of Al:NbTi:Cu of the conductor is 24:1:1. The design current of the conductor is 4.5 kA at 1.5 Tesla. Measured velocities are 30, 65, and 90 m/s in the direction of the conductor at 2020, 3030, and 3540 A, respectively. Thermal distributions inside the coil after quenches were quite uniform and no local overheating was observed.