Heat pulses required to quench a potted superconducting magnet

The Navy is presently considering the use of fully potted Niobium Titanium superconducting magnets for the field windings of electric motors and generators. These magnets will operate at fields of 6.5 tesla and will be subjected to shipboard shock and vibration. This shock, vibration or other mechanical perturbation can result in energy being imparted to the superconductor within the magnet. If this energy is sufficiently large, the temperature will rise locally driving the conductor normal. If the normal zone is larger than the minimum propagating zone, thermal runaway will occur and a magnet quench will result. A potted superconducting magnet was constructed to determine the amount of energy input required to produce a quench. The magnet was wound from multifilament Nb-Ti conductor, reenforced with fiberglass cloth, and vacuum impregnated with epoxy resin. Several heaters were embedded in the winding and the energy required to drive the magnet normal was measured at various magnetic fields and current levels. Energy pulse widths were varied over a wide range to examine the effects of thermal diffusion and cover a broad spectrum of possible energy inputs. The results are compared with magnet operating characteristics and general design limits are discussed.