Investigating thermal hydraulic quenchback in a cable-in-conduit superconductor

Quench propagation of a cable-in-conduit force-cooled superconductor plays a very important role in the protection of a magnet built with such a conductor as in a superconducting magnetic energy storage (SMES) system. Some thermal analysis showed that the compressional and frictional heating exerted by the expanding hot helium could heat the helium away from the normal zone above the superconductor current sharing temperature. Thus, an acceleration of the quench propagation could be realized. This phenomenon is called thermal hydraulic quenchback (THQ). A setup was built specifically to investigate this phenomenon. The test sample consists of a 50 m long NbTi superconducting cable enclosed in a stainless steel conduit. Heaters 0.2 to 8 m long are provided to quench the conductor. The authors report experimental finding of THQ and its dependence on the initial normal zone length, the conductor current, the magnetic field, and the coolant temperature. >