"Training Quench" is a very important part of magnet operation. Commercial magnets trained at the factory before they are shipped and no further training is needed. During the initial charging of the magnet, the magnet often quench when it is below the designed current value. This phenomenon is solved by "Traning" the magnet.
The specific heat of the superconductor at 4.2k is very small, of the order of 10e-4J /g/K, so any small thermal-mechanical disturbance in the magnet will generate heat and generate a hot spot, which will cause the temperature of the superconductor to exceed its critical temperature Tc. If the hot spot cannot be reduced or dispersed, the magnet will lose its superconducting state (quench).
A superconducting coil is a complex of materials such as superconductors themselves, insulating layers of resin, and so on. These materials have very different thermal shrinkage coefficients. During the cooling process, fractures occur under the action of the large Lorentz force, resulting in cracks in the resin that release enough strain energy to cause the quench. After the release of the strain energy, a similar phenomenon occurs again during the charging (ramp up) process in the next stage. The magnet is charged to a higher current. This process is repeated until the design current of the magnet is achieved.
Reference: "Superconductivity Basics and Applications to Magnets" by R.G. Sharma