Rapid normal zone propagation observed in a 13 T-46 kA NbAl cable-in-conduit conductor

Koizumi, Norikiyo; Matsui, Kunihiro; Kume, Etsuo ; Okuno, Kiyoshi

The NbAl Insert was developed by JAERI aiming at the demonstration of a NbAl conductor to fusion reactor magnets. A quench test was performed on the NbAl Insert at 13 T with various temperature margins, which are defined as a difference between current sharing temperature and operating temperature. The initial normalcy was initiated by using an inductive heater and a coil current was kept for several seconds. The normal zone propagation velocity was accelerated after 3 s from the onset of heating in case that the temperature margin was set at 0.5 K. A simulation using one-dimensional stability and quench simulation code was performed. The calculation results indicate that such rapid propagation occurred due to a temperature rise beyond a current sharing temperature because of a large pressure increase even at the location where the normal front did not reach yet. This large pressure rise was caused since the coolant was contained in the closed circulation circuit of the cooling system, which is usually applied to a large magnet cooling system.