FEM models and Fourier decomposition of three thick septa

TL;DR

This paper presents FEM models and Fourier analysis of thick septa in the CEBAF accelerator, introducing a new septum design with improved magnetic field properties and lower current density.

Contribution

The paper develops detailed FEM models of existing and novel thick septa, proposing a new septum concept with comparable field quality and reduced current density.

Findings

New septum design has higher-order field components within a factor of two of existing models.

The new concept offers better harmonic content and lower current density in certain accelerator layouts.

FEM models effectively analyze magnetic field distributions of thick septa.

Abstract

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.