| 摘要 |
PURPOSE:To improve a linearity of a magnetic field by a method wherein a distance from a facing end surface to the center of a coil and a distance from the facing end surface to the center of a pole piece of the coil are obtained taking primary image currents into account and the coil is provided to the point whose distance from the center of the pole piece is determined by the above two distances. CONSTITUTION:A third grade magnetic field differential component, taking image currents into account, is expressed by an equation I . If the primary image currents 4a, 4b, which deteriorate a linearity of the magnetic field most, only are considered, the equation I is replaced by the equation II. A solution Yo which makes the equation IIzero is obtained. If a coil current Ix is provided to the position Yo, a coil which produces a linear magnetic field differential Bz/differential Y which is obtained by taking the primary image currents into account can be produced. In the equation, muo means a permeability of a vacuum, Ix means a coil current, Zo means a Z-axis distance from the center of a pole piece to the center of a coil line, Yo means a Y-axis direction from the center of the pole piece to the position of the coil and (a) means a Z-axis distance from the center of the coil line to an end surface of the pole piece. With this constitution, as the coil is arranged taking image currents into acount, the linearity of the magnetic field is significantly improved. |
