High-chromaticity Optics for the MAX IV 3 GeV Storage Ring

Abstract: The MAX IV facility is a 3rd generation state-of-the-art synchrotron light source currently under construction in Lund, Sweden. The MAX IV 3 GeV storage ring has a large negative natural chromaticity, which has to be corrected to positive values to prevent head-tail instabilities. On the other hand, high linear chromaticity can lead to a large tune footprint limiting Touschek lifetime. Therefore, the linear chromaticity is corrected to +1 in both planes with sextupoles while both sextupoles and octupoles are used to optimise the tune footprint. Studies indicate this design leads to threshold currents for resistive wall and transverse mode coupling instabilities beyond what is expected during regular user operation. However, since these are preliminary studies based on several approximations, the possibility of instability issues during commissioning needs to be considered. A short term solution is to operate the storage ring at a higher chromaticity. This thesis describes the development of a high-chromaticity optics for the MAX IV 3 GeV storage ring with linear chromaticity +4 in both planes. It focuses on reduction of chromatic and amplitude-dependent tune shifts to maximize dynamic aperture and Touschek lifetime. A comparison between the performance of the high-chromaticity optics and the design optics is also presented. The analysis reveals that the performance of the developed high-chromaticity optics is, not quite unexpectedly, poorer than the performance of the design optics. However, the performance of the high-chromaticity optics is estimated to be sufficient to allow the optics to be applied in the MAX IV 3 GeV storage ring as a short term solution if instability issues should occur during commissioning.