Field Correction of a Quadrupole Magnet and a Skew-Quadrupole Magnet By Using Iron Plates Attached to the End Shaping

Abstract

It is well known that magnetic field linearities of the conventional quadrupole magnet and the skew-quadrupole magnet are improved by the end shaping of the pole. We found that small iron plates which were attached to the end shaping changed field distributions and radial and azimuthal multipole error components were cancelled by selecting the optimum mass of iron plates. The optimum mass was determined from a few field measurements easily. In addition, we found that the transverse distribution of the field gradient of the quadrupole magnet changed concavely according to increasing iron plates and the that distribution of the skew-quadrupole magnet changed convexly in reverse. This difference of the change of the field is due to the difference of the sign of the dodecapole error component between the quadrupole magnet and the skew-quadrupole magnet