Nmr magnet system with superconducting coil in a helium bath

摘要

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 (101) of a cryostat in supercooled liquid helium at a temperature of less than 4.2 K, with the cryostat having at least one further chamber (102) containing liquid helium that is essentially at atmospheric pressure with a temperature of approximately 4.2 K, 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 (106) with which the liquid helium can be cooled to a temperature T << 4.2 K, especially to T APPROX 1.8 - 2.3 K, is provided in the first chamber. Helium pumped from the refrigerator (106) passes via inlet (161) into an annular heat exchanger (130) in a tower (131) and to an outlet (162). Radiation shields (121, 122) are thermally coupled to the heat exchanger (130). Helium evaporating from the upper chamber (102) leaves the tower (131) through outlet (163). Preferably the cryostat includes three towers (131).