| 摘要 |
PURPOSE:To generate a magnetic field having high uniformity by forming a projection in approximately 0.06 thickness and approximately 0.8 width at the nose section of a pole piece. CONSTITUTION:When a secondary magnetic-field coefficient F2 to the width W of a projection 2 is calculated while using the thickness (d) of the projection 2 as a parameter and a quaternary magnetic-field coefficent F4 to the width W is obtained, the combination of (d) and W through which F2 and F4 are brought to 0 simultaneously is formed under conditions corresponding to the intersection of the loci of both roots, dapprox.=0.06 and Wapprox.=0.8. The projection having thickness (d) and width W is formed by shimming a pole piece. When the distribution of magnetic field strength in the (r) direction in a central surface S is measured to a magnet device consisting of pole posts 3, a yoke 4 and exciting ciils 5 and the deviation is represented by the ratio (h) to Bz(O), extremetly excellent uniformity of approximately 10<5> is obtained. |
