In superconducting magnets, variations in magnetic fields and temperature are common occurrences which often cause conduction faults in superconducting filaments. To compensate for such conducting faults, the magnetic windings are usually formed of wires in which the superconducting filaments are encased in a metal, such as silver, copper or aluminum, which is normally conductive across a wide range of temperatures, including superconducting temperatures. The metal electrically stabilizes the wire by shunting any portion of the filament(s) which has become non-superconducting. Furthermore, the encasing metal has good thermal conductivity, tending to transfer heat away from hot spots in the windings. Nevertheless, events, such as flux jumps, wire motion or eddy currents, in the superconducting filaments or encasing metal produce heat which may lead to a precipitous normalization of superconductive windings. Such temperature excursions occur during periods measured in microseconds, such short periods being insufficient for dissipation of the heat to the coolant, e.g., liquid helium.
To reduce the probability of normalizing temperature excursions, U.S. Pat. No. 4,171,464 proposes that particles or fibers of gadolinium oxide or gadolinium-aluminum oxide be incorporated in the metal, e.g., copper, that encases the superconducting filaments. These materials have high heat capacities at superconducting temperatures, e.g., below about 5.degree. K., and thus tend to absorb substantial amounts of locally produced heat. Furthermore, these materials undergo antiferromagnetic transitions within the superconducting temperature range, and when a decrease in the magnetic field occurs as a result of a conduction fault, the specific heat of the material increases, enhancing the adiabatic stabilization.
However, adiabatic thermal stabilization through adiabatic demagnetization by compositions, such as the gadolinium and gadolinium-aluminum oxides which undergo antiferromagnetic transitions, is only realized if the effective magnetic field experienced by the material decreases. Thus, the material is less efficient in preventing precipitous normalizations in circumstances where a localized normalization of the superconducting filaments occurs but does not produce an immediate change in the magnetic fields to which the thermal stabilizer is subjected.
Furthermore, because the magnetically affected contributions to heat capacity of materials, such as gadolinium oxides, are a substantial portion of the total heat capacity and because these components of their total heat capacity decrease with increasing magnetic field, these materials are less useful for thermal stabilization in superconducting applications where very intense magnetic fields are produced. As noted in the above-mentioned '464 patent, Gd.sub.2 O.sub.3 has substantially less heat capacity in a 2.4 Tesla (Tesla=10,000 Gauss) field than in a 0 Tesla field. Many present day superconducting magnet applications require substantially higher magnetic fields; for example, at the present time, superconductng magnets for fusion applications may produce magnetic fields in the range of 15 Tesla. At such magnetic field intensities, the heat capacities of materials, such as Gd.sub.2 O.sub.3, having large magnetic field-affected components of heat capacity, will be severely depressed.
There is a need for materials for use in superconducting applications which have high heat capacities and which are substantially unaffected by the magnetic field.