Dipole septum magnet in the fast kicker system for multi-axis advanced radiography

Here we present designs for a static septum magnet with two adjacent apertures where ideally one aperture has a uniform dipole field and the other zero field. Two designs are considered. One is a true septum magnet with a thin layer of coils and materials separating the dipole field region from the null field region. During the beam switching process, the intense electron beam will spray across this material septum leading to concerns on beam control, vacuum quality, radiation damage, etc. due to the lost particles. Therefore, another configuration without a material septum is also considered. With this configuration it is more difficult to achieve high field quality near the transition region. Shaped shims are designed to limit the degradation of beam quality (emittance growth). Simulations are performed to obtain the magnetic field profile in both designs. A PIC simulation is used to transport a beam slice consisting of several thousand particles through the magnet to estimate emittance growth in the magnet due to the field non-uniformity.