The use of correcting coils in end magnets of accelerators

The end magnets of the race-track microtron booster, which is the second stage of the 30.0 MeV cw electron accelerator under construction at IFUSP, play a fundamental role in terms of the beam quality. The use of correcting coils, based on the inhomogeneities of the magnetic field and attached to the pole faces, assured uniformity of 10^-5. We present the performance of these coils when operating the end magnets with currents that differ in ±10% from the one used in the mappings that originated the coils copper leads. For one of the magnets, adjusting conveniently the current of the correcting coils, made it possible to homogenize field distributions of different intensities, once their shapes are practically identical to those that originated the coils. For the other one, the shapes are changed and the coils are less efficient. This is related to intrinsic factors that determine the inhomogeneities. However, in both cases we obtained uniformity of 10^-5, much better than necessary