Studies On Diffraction-Limited Storage Ring Lattices And Related Dynamics

As the user’s requirement for high brightness and coherence of synchrotron radiation improving,storage ring light sourcs have developed into the fourth generation——diffraction-limited storage rings(DLSRs),of which the beam emittance so far is about hundreds of picometers or even tens picometers.The lattice is the basis of the physics design of the storage ring and the emittance,brightness,injection efficiency,beam lifetime and many other performances are mainly decided by the lattice.To reduce the emittance dramatically,multi-bend achromat(MBA)lattices have been widely used in the design of DLSRs.While at the same time as lowering the emittance,the nonlinear dynamics performance deteriorates seriously.Then,many kinds of lattices and cancellation strategies for nonlinear dynamics effects were proposed worldwide in order to obtain lattices with both ultra-low emittances and good nonlinear dynamics performances.From the characteristic of chromaticity-correction point of view,these lattices can be divided into hybrid MBA lattices with lumped chromaticity-corrections,traditional MBA lattices with distributed chromaticity-corrections(e.g.,the MAX IV lattice)and the MBA lattices with semi-distributed chromaticity-corrections which are compromises between the former ones.In this dissertation,we will study the DLSR lattices and related dynamics.To be specific,we will develop new design methods and extend or improve some existing lattices and propose some new lattices.Firstly,when the linear lattices of hybrid MBA lattices have been fixed,there is little potential for nonlinear dynamics optimization and it is difficult to get a large momentum aperture.On the other hand,the beta functions at the three families of chromatic sextupoles have the same variation trends.To further improve the performance of hybrid MBA lattices,a new design method is developed based on the structural features.By optimizing the nonlinear dynamics indicators,the linear lattice solutions with a rich diversity are obtained and we can suppress the nonlinear dynamics effects in the linear lattice design if appropriate values of indicators are selected.This method is employed in designing lattices of two DLSRs and the results show that the low emittance lattices with both a large dynamic aperture(DA)and a large momentum aperture can be efficiently got by using this method.Then extensions are made based on hybrid MBA lattices.One is the case with M>7 and then hybrid 10BA lattices with two kinds of phase advances are studied.Another is a combination with double-bend achromat(DBA)lattices and hybrid MBA lattices to reduce the emittance and preserve considerable straight sections simultaneously.In this study,a double DBA-hybrid 6BA lattice is designed for HLS-II storage ring.Next,taking higher-order achromat(HOA)MBA lattices and locally symmetric MBA lattices as examples,the characteristic and dynamics performance of traditional MBA lattices with distributed chromaticity-corrections are studied.An HOA 6BA lattice and a locally symmetric 6BA are designed based on the beam energy of Hefei Advanced Light Source and then a comprehensive comparison for linear parameters and nonlinear dynamics performance among several MBA lattices are made.The results show that the DA for particles with nominal energy is not large,but the DA for off-momentum particles and the DA with longitudinal motion considered will not shrink too much.Besides,by breaking the perfect cancellation for driving terms,better nonlinear dynamics performance can be got with sextupoles divided into more families.Finally,inspired by the MBA lattices with interleaved dispersion bumps and locally symmetric MBA lattices,some new MBA lattices with semi-distributed chromaticity-corrections are proposed based on the cancellation strategy with local symmetry and-Ⅰ transformation,for the sake of a balance between the features of hybrid MBA lattices and traditional MBA lattices.Specifically,a preliminary study is carried out taking an 8BA lattice and an 11BA lattice as examples and the results show that this kind of lattices have many knobs for nonlinear dynamics optimization and acceptable DAs.These new MBA lattices can be a reference for or applied in the design of other DLSRs.