FEM models and Fourier decomposition of three thick septa

The CEBAF recirculating linear accelerator uses 26 septa: 8 thin, 17 thick and one Lambertson. We report here on detailed FEM models of one thick current-sheet septum, the Lambertson, and a new thick-septum concept which contains features of both. The last has higher-order field components within a factor of two of the current-sheet septum and much lower current density in the conductor were it used as a drop-in replacement in CEBAF. There are accelerator layouts in which the new concept is superior to the current sheet septum in both harmonic content and current density.