The IFUSP race-track microtron booster accelerator end magnets antisymmetric perturbations

We will present measurements and calculations related to the antisymmetric perturbations, and comparisons with the symmetric ones, of the IFUSP race-t rack microtron booster accelerator end magnets. These perturbations were me asured in planes situated at +/-12 mm of the middle plane, in a gap height of 4 cm, for a field distribution of about 0.1 T. The measurements were don e in 1170 points, separated by a distance of 8 mm, using an automated syste m with a +/-1.5 mu T differential Hall probe. The race-track microtron boos ter is the second stage of the 30.0 MeV electron accelerator under construc tion at the Linear Accelerator Laboratory in which the required uniformity for the magnetic field is of about 10(-3). The method of correction employe d to homogenize the IFUSP race-track microtron booster accelerator magnets assures uniformity of 10(-5) in an average field of 0.1 T, over an area of 700 cm(2). This method uses the principle of attaching to the pole pieces c orrection coils produced by etching techniques, with copper leads shaped li ke the isofield lines of the normal component of the magnetic field measure d. The ideal planes, in which these measurements are done, are calculated a nd depend on the behavior of the magnetic field perturbations: symmetric or antisymmetric with reference to the middle plane of the magnet gap. These calculations are presented in this work and show that for antisymmetric per turbations there is no ideal plane for the correction of the magnetic field ; for the symmetric one, these planes are at +/-60% of the half gap height, from the middle plane. So this method of correction is not feasible for an tisymmetric perturbations, as will be shown. Besides, the correction of the symmetric portion of the field distribution does not influence the antisym metric one, which almost does not change, and corroborates the theoretical predictions. We found antisymmetric perturbations of small intensity only i n one of the two end magnets. However, they are not detected at +/- 1 mm of the middle plane and will not damage the electron beam.