Magnetic cross-talk simulation between Q2 and L-bend magnets of APS-U

Abstract

The Advanced Photon Source Upgrade project (APS-U) will replace the present storage ring of the Advanced Photon Source (APS) with a new storage ring based on a multi-bend achromat (MBA) lattice. Due to the increased number of magnets in each sector of the MBA lattice, the space between magnets is very limited, with the smallest separation between magnets being only 5 cm between the Q2 quadrupole in the doublet section and the adjacent M1 longitudinal gradient dipole (L-bend). Cross-talk between these magnets is of concern and is investigated in this work. Both magnets are modeled separately in Opera-3D, and then together as per their design layout in the MBA lattice. The trajectory of a 6.0 GeV electron beam through both magnets is calculated, the local field multipoles along that trajectory computed, and the integrated harmonics compared with a superposition of the fields in the individual magnets. These simulations show that the integrated quadrupole field of the Q2 magnet drops by 0.16% due to the presence of the M1, while the integrated dipole field of the M1 is practically unaffected. The effect on the higher-order multipoles at a radius of 10 mm was less than 0.01% of the integrated dipole field, and is within acceptable limits. The detailed magnetic structures of the Q2 and the M1, electron beam trajectory through these magnets, the local main and harmonic fields along the trajectory, and their integrals with and without cross-talk are reported.