Lattice study for the HLS-II storage ring *

The Hefei Light Source (HLS) is undergoing a major upgrade project, named HLS-II, to obtain lower emittance and more insertion device straight sections. Undulators are the main insertion devices in the HLS-II storage ring. In this paper, based on the built database of lattice parameters for the HLS-II storage ring obtained by the global scan method, we use the quantity related to the brightness of undulator radiation to more directly search for high brightness lattices. Lattice solutions for achromatic and non-achromatic modes have been easily found with lower emittance, smaller beta functions at the center of insertion device straight sections and lower dispersion in non-zero dispersion straight sections compared with the previous lattice solutions. In this paper, the superperiod lattice with alternating high and low horizontal beta functions in long straight sections for the achromatic mode is studied using the multiobjective particle swarm optimization algorithm.