A magnet model for a hybrid undulator assembly

A modelling method, in which a single magnet block is divided into several sub-blocks, is described. It is assumed that each sub-block is polarized homogeneously. The sub-block polarizations are derived with a genetic algorithm, which analytically calculates the total magnet flux density values generated by all sub-blocks and fits it to the values measured at the corresponding points in the vicinity of the magnet. The sub-block modellings accomplished show notable improvement in predicting the magnet flux density within the undulator gap when compared with a model based on homogeneously polarized blocks. The sub-block model can also be used when discarding bad magnets from a set. Finally, the results show that the inhomogeneities in individual magnets are one of the major reasons for poor predictability of the undulator field in hybrid devices.