Conceptual Design of Superbend and Hardbend Magnets for Advance Light Source Upgrade Project

Abstract

ALS-U is an ongoing upgrade of the Advance Light Source (ALS) at Lawrence Berkeley National Laboratory (LBL). The upgraded ring of the ALS will use a multi-bend-archomat (MBA) lattice, which will allow increasing the brightness of soft x-ray sources 2-3 orders of magnitude with respect to current ALS ca-pabilities. One of the goals of the project is maintaining support for existing x-ray beamlines with useful intensity around 12.5 keV, which are used for a macromolecular crystallography. The medium energy x-ray source points will be provided by replacing six gradient-dipole magnets of the upgraded ring with high-field magnets generating a higher peak field at the source point. Two defocusing quadrupoles will be installed together with each high-field magnet in order to match the quadrupole field component of removed gradient dipole. Two alternative designs were investigated. The first design is a warm-bore superconducting magnet. Its coils are made of an internally reinforced bronze-route Nb 3 Sn wire and a holmium pole is used as a flux concentrator. The second option is NdFeB permanent magnet system with build-in field clamps. Due to limited space in the accelerator lattice and the magnetic field requirements for the x-ray source points, both designs present challenges due to high magnetic forces acting on the magnet components and due to impact of the magnet cross-talk on the beam trajectory.