| 摘要 |
PROBLEM TO BE SOLVED: To provide an electromagnet unit comprising a shim coil which is capable of generating such a correction magnetic field as canceling a disturbance magnetic field.SOLUTION: An electromagnet unit comprises a plurality of magnetostatic coils of which the center axes are matched to each other, and generates magnetostatic fields in parallel with the center axes in a uniform magnetic field region. The electromagnet unit further comprises a plurality of shim coils (No.1 to No.6) for improving uniformity of magnetic fields in the uniform magnetic field region by generating a magnetic field which is capable of canceling magnetic fields in an arbitrary radial direction of the magnetostatic coils approximately vertical to the center axes generated in the uniform magnetic field region. The magnetostatic coil is a superconducting coil and the shim coil 1 includes the superconducting coil. Magnetic flux storage in a superconducting state of the superconducting coils is utilized to passively cancel an error magnetic field caused by the outside. The superconducting coils of the magnetostatic coils and the shim coils 1 are operated under a permanent current mode. |
