Modern synchrotron light sources are competing intensively to increase X-ray brightness and, eventually, approach the diffraction limit, which sets the final goal of lattice emittance. Recently, we propose a new optics solution aimed at reaching low emittance, using a lattice element “Complex Bend”. The Complex Bend is a sequence of dipole poles interleaved with strong alternate focusing so as to maintain the beta-function and dispersion oscillating at low values. By integrating this element at low emittance lattice, the designed emittance is around 30 pm-rad. To prove the feasibility of this new design, we designed and fabricated the key element, prototype complex bend, with gradient at 140 T/m. It was installed in the beam line with 100-200 MeV beam energy at NSLS-II linac beamline and beam commissioned started in Jan. 2023. In this paper, we report the beam commissioning result.

Nonlinear lattice optimization and correction become increasingly important as storage ring light sources continue to push towards ultra-low emittances. An advanced algorithm based on machine learning technique, called multi-generation Gaussian process optimizer (MG-GPO), was applied to find optimal nonlinear lattice solutions, and was demonstrated to outperform traditional algorithms. It was also implemented in online optimization and resulted in improved machine performance. The need to drive and maintain large beam oscillation amplitude for nonlinear beam dynamics measurement and correction motivated the study of resonant driving with swept frequency. We discovered that there exists a drive amplitude threshold for successful beam excitation. The dependence of the threshold on frequency sweep rate and lattice parameters is theoretically analyzed. The results were verified by both simulations and experimental data.

The demands of a higher brightness photon beam push the electron beam emittance of storage rings towards a diffraction-limited level. The concept of multi-bend achromat (MBA) structure and its variations, containing multiple dipoles in a cell, has been widely employed in the fourth-generation storage ring light sources. Recently, a novel concept of lattice structure, called complex bend lattice, extends the option for low emittance ring lattice design. This paper presents the developed low-emittance complex bend lattices. The benefits of using complex bends include low natural emittance, long straights for IDs, more free space for accelerator equipment, and reduced power consumption for magnets.

Misalignment of magnets in the storage rings causes trajectory deviation when the beam traverses through magnets, resulting in the degraded performance of linear optics and nonlinear dynamics. The beam-based alignment (BBA) technique is commonly used to steer the beam passing through the centers of magnets. Recently, a new method has been developed to determine the centers of multiple magnets simultaneously [1]. In this paper, the test of this fast BBA method at NSLS-II is presented.