Abstract: A magnet system for providing a substantially homogeneous magnetic field in a region. The magnet system includes a main coil and a pair of correcting coils with the main coil generating a magnetic field in a zone including the region. The correcting coils are at first and second locations in the zone and are connected to one another so that a magnetic field generated by the main coil will induce currents in the correcting coils which oppose one another. The correcting coils are constructed so that there will be no resultant current in them when there is generated substantially the same field strength of both of the first and second locations. Thus, the generation of differing magnetic field strengths at the respective locations effects generation of a resultant current in the correcting coil causing strengthening of the magnetic field at the location having the lesser magnetic field strength and weakening of the magnetic field at the other location, making the net field relatively homogeneous.

Abstract: Methods and apparatus are provided for minimizing heat introduced by electrical leads into the cryogenic liquid in which a superconducting magnet is immersed. The electrical leads have normal portions extending from exterior of the cryogenic liquid containment vessel and thereinto and superconducting portions extending vertically downward therefrom and connected to the magnet. Means are provided to lower and raise the level of cryogenic liquid around the superconducting portions of the leads to fully immerse the supercoducting portions during periods of magnet energization and expose selected segments thereof when the magnet is de-energized. When exposed, the non-immersed segments provide a thermal resistance between the normal metal portions and the cryogenic liquid.