Experimental Study on Quench Detection and Protection Conditions of Copper-Stabilized Coated Conductors Using Short Samples

In order to clarify the conditions for successful quench detection and protection of magnets wound with REBa
₂
Cu
₃
O
_y
(RE-123) coated conductors, experiments using short samples of copper-stabilized coated conductors were performed. A short sample of coated conductor was conduction-cooled to 30 K, a magnetic field was applied (μ
₀
H up to 2 T), a current was supplied, and subsequently quench was initiated using a small heater. When a normal voltage (over a preset threshold) was detected, the supplied current would be decreased exponentially. This procedure simulated the conventional quench detection (detecting voltage) and protection (using a dump resistor; current decaying exponentially with a time constant = coil inductance/resistance of dump resistor) for superconducting magnets. We examined how the critical current, time constant of current decrease, and voltage threshold for quench detection affected the hot-spot temperature. By comparing the critical currents and n values of a sample before and after quench, we identified the maximum current at which the sample exhibited no degradation (not-degrading current). The effect of transverse thermal diffusion and longitudinal thermal conduction was evaluated using one-dimensional/zero-dimensional quench simulation. The conditions for successful quench detection and protection were evaluated using not-degrading currents as well as the current at which the maximum hot-spot temperature reached 300 K.