A SUPERCONDUCTING SOLENOID SYSTEM WHICH CANCELS FLUCTUATIONS IN THE AMBIENT MAGNETIC-FIELD

An extra superconducting coil added to a standard, high-field solenoid results in a self-shielding solenoid system which utilizes flux conservation to passively shield an interior volume from changes in the ambient field, such as those from elevators or subways. For this first experimental demonstration, a highly homogeneous 6 T solenoid and an added coil were arranged in one of the geometries predicted to produce effective shielding. The fluctuations in the shielded high-field region are observed to be smaller than the fluctuations in the spatially uniform ambient magnetic field by a large factor of 156, confirming the general shielding principles presented earlier. This shielding is crucial for ongoing antiproton cyclotron resonance experiments and should be useful for nuclear magnetic resonance experiments and ion cyclotron resonance experiments and for other applications where high field and high stability are required simultaneously. © 1991.