A method and apparatus are provided for protecting a superconducting magnetic energy storage system having a coil from damage caused by a change of state of at least a portion of the coil from superconducting to normal conducting, and the consequent conversion of stored electrical energy to heat. A thermal capacitance is placed in thermal contact with the coil. The thermal capacitance is formed of a substance, such as nitrogen, which is solid at operating pressure at a temperature substantially above the transition temperature of the coil and that vaporizes below the temperature at which the system is damaged. The volume of the substance is sufficient to provide thermal capacity upon vaporization of the substance to dissipate substantially all of the stored energy without permitting the system to overheat. Liquid helium is provided in thermal contact with the substance and the coil for normally cooling the coil and the thermal capacitance to a temperature which is low enough so that the coil is in its superconducting state and the substance becomes substantially solid. Means are also provided for propagating any normal conducting region that is present for more than a very short time over substantially all of the coil by removing the helium from thermal contact with a substantial portion of the coil. In this manner, the substance absorbs the stored energy while maintaining the temperature of the system below the temperature at which it is damaged.