A Cross-Cell Interleaved Nonlinear Lattice for Potential NSLS-II Upgrade

Abstract

An interleaved sextupole scheme using a cross-cell betatron phase cancellation technique is adopted as a candidate for a future upgrade to the NSLS-II lattice. The upgraded lattice will use as many NSLS-II installed magnets as possible, including 30 dipoles, which will create a triple bend achromat configuration. A 300 pm-rad horizontal beam emittance has already been achieved with the current configuration. The emittance can be further reduced to around 200 pm-rad with damping wigglers. Some new design concepts used in modern 4th-generation light sources, such as adopting longitudinal gradient bends and reverse bends, are incorporated into the design as well. The betatron phase-advance between sextupoles is designed to have a cross-cell interleaved cancellation pattern in the transverse planes. The dynamic aperture is sufficient to allow the conventional off-axis top-off injection. At the same time, a large energy acceptance looks promising and would ensure a sufficiently long beam lifetime.