| 摘要 |
PURPOSE:To minimize magnetic field components unnecessary for correcting an unequal magnetic field by mounting another linear current path in parallel with a linear current path of a saddle-shaped coil constituting a correcting coil and flowing currents so that magnetic fields generated from both current paths cancel each other out. CONSTITUTION:A ZX shim coil 6 is constituted by each one pair of first and second saddle-shaped coils 7a, 7b arranged on straight lines while holding a high uniform magnetic field region 3, and each one pair of saddle-shaped coils 7a, 7b are disposed symmetrically to ZX surfaces. The ampere-turns of four saddle-shaped coils as the first and second saddle-shaped coils 7a, 7b are mutual equal. The directions of currents are determined so that the direction of the currents of the ZX shim coil and the directions of arcuate section currents on the sides near to the high uniform magnetic field region 3 of the saddle-shaped coils 7a, 7b are equalized. Arcuate sections on the sides near to the high uniform magnetic field region 3 of the saddle-shaped coils 7a, 7b may be arranged at the same position as the arcuate section of the ZX shim coil. It is preferable that the linear sections of the saddle-shaped coils 7a, 7b may be lengthened as much as possible, but short linear sections are sufficient enough when magnetic field correction outputs may be of small value. |
