Superconducting magnet assemblies.

摘要

A superconducting magnet assembly including a hollow, cylindrical vacuum vessel (40). An annular, liquid helium holding low temperature reservoir (60) extends centrally through the vacuum vessel, but is sealed therefrom such that liquid helium is not drawn into the vacuum. A plurality of annular superconducting magnets (56) are received in the low temperature reservoir immersed in the liquid helium, the magnets producing a field in the bore of the vacuum vessel. A first cold shield (44) and a second cold shield (50) are mounted in the vacuum vessel surrounding the low temperature reservoir. A main magnetic field shield coil (66) is disposed in the low temperature reservoir outside of the annular superconducting magnets for canceling the magnetic field generated by the annular magnets surrounding the magnet. A gradient shield coil (70) is mounted in the low temperature reservoir inside the annular superconducting magnets to cancel magnetic fields generated by gradient magnetic field coils (14) in the region beyond the gradient shield coil, the gradient field coils imposing a gradient on the field produced in the bore by the annular superconducting magnets. The gradient shield coil is electromagnetically coupled to the gradient field coils to be driven by magnetic fields emanating therefrom. Optionally, the gradient shield coil can be constructed of a higher temperature superconducting material and disposed in association with one of the cold shields. <IMAGE>