Abstract: In an NMR magnet system for generating a highly homogeneous magnetic field of high field strength, with at least one superconducting magnet coil which is arranged in a first chamber of a cryostat in supercooled liquid helium at a temperature of less than 4.2K, with the cryostat having at least one further chamber containing liquid helium that is essentially at atmospheric pressure with a temperature of approximately 4.2K, the first chamber is connected to the further chamber in such a way that the supercooled liquid helium located in the first chamber is also essentially at atmospheric pressure. A refrigerator with which the liquid helium can be cooled to a temperature T<<4.2K, especially to T.apprxeq.1.8-2.3K, is provided in the first chamber.

Abstract: Multifilament superconductors of brittle, prereacted Nb.sub.3 Sn filaments in a bronze matrix wherein the electrical power under superconductive conditions is stabilized. The superconductor comprises a core of Nb.sub.3 Sn multifilaments and a bridge containing a band of purest aluminum which is soldered in parallel to the superconductor core.