Simulation of a magnetic field correction scheme for a Halbach-type undulator

An electron-beam trajectory in a Halbach-type undulator with simulated magnetization errors in its component magnet blocks has been calculated using a three-dimensional magnetic field calculation program. The errors taken into account were deviations of the magnetization strength from a nominal value and a deviation of the magnetization direction from a nominal axis. Both uniform and Gaussian distributions of the error magnitudes are assumed for the component magnet blocks of an ideal reference undulator. A simple method for rearranging magnet pairs is discovered. The field integrals are reduced by factors of 4–15 on the average with the method, and the local distortion of the trajectory is strongly corrected. It is found that the distortion of the trajectory in the corrected undulator is almost independent of the magnet gap.