Patent ID: 7135948

Claim:
An actively shielded superconducting magnet comprising: at least one main coil having a central axis, said main coil producing a central magnetic field and a far fringe field when energized; at least one shield coil having a central axis generally parallel to the central axis of the main coil, said shield coil being positioned substantially concentrically outside of the main coil and producing an opposing magnetic field when energized for substantially reducing the far fringe field; and at least one dipole shim coil having a central axis generally parallel to the central axes of the main and shield coils, said dipole shim coil being positioned substantially concentrically outside of the main coil and producing an additional magnetic field when energized for adjusting and fine-tuning the far fringe field that has been substantially reduced by the first magnetic field of the shield coil, and wherein the main coil has a first radius and the shield coil and dipole shim coil have a second radius, said second radius being greater than the first radius.