Small-emittance and low-beta lattice designs and optimizations

Abstract

This paper uses the advanced light source (ALS) storage-ring lattice as an example to illustrate the strategies and techniques that we developed for lattice design and optimization. First, the theoretical minimum emittance (TME) theory is applied to optimize the ALS storage-ring lattice for its future upgrades. The study confirms the results found in earlier study using both global scan of all stable settings and multiobjective genetic algorithms (MOGA) techniques. It is shown that, using TME, the ALS natural emittance can be reduced to an even smaller value by introducing additional quadrupoles to the straight, which is unknown in previous studies. Then, the nonlinear properties of the lattice are optimized using MOGA. Instead of the conventionally used dynamic aperture area, the total diffusion rate of the lattice is used as an objective in the optimization, which leads to a superior performance in nonlinear beam dynamics. Finally, to find a best overall working lattice for ALS future upgrades, the linear and nonlinear properties of the lattice are optimized simultaneously using MOGA. Compared to the widely used dynamic aperture tune scan technique, MOGA not only allows us to rapidly find a best working point in a wide searching range, but also provides us trade-offs among the optimization objectives, such as the low emittance, small beta function, and large dynamic aperture. These trade-offs give us a guideline to choose a candidate lattice for ALS future upgrades. The strategies and techniques presented in this paper are not limited to the ALS, and can be adopted to other facilities.