STUDY OF FODO STRUCTURES FOR A SYNCHROTRON LIGHT SOURCE

Synchrotron radiation is a helpful tool to Investigate a wide range of physical, chemical and biological phenomena. Extremely high flux, brilliance synchrotron radiation can be achieved in low emittance electron storage rings with wigglers and undulators. The Advanced Light Source (ALS) is a synchrotron radiation source with 1.5 GeV design energy. The lattice is designed with 12 superperiods each containing a 6 m long straight section to accomodate the insertion devices. Two straight sections are reserved for injection elements and accelerating cavities. To minimize source width and angular divergence the dispersion is matched to zero in the straight sections. The goals for the design of such a lattice are low emittance, flexibility and large dynamic apertures after chromaticity correction, at low cost. The most economical, and therefore most frequently used structure in the past is that suggested by Chasman and Green. It has become apparent recently that alternative designs with excellent characteristics have been proposed for synchrotron light sources. Therefore a new lattice design study for the ALS has been carried out. The Triple Bend Achromat (TBA) lattice proposed by Vignola has been compared with the Chasman-Green lattice. An expanded Chasman-Green lattice proposed by Hutton was reviewed for the ALS. Finally the FODO achromat lattice as proposed by Wiedemann for the SSRL has been studied as a candidate for the ALS. The results for the FODO achromat lattice are presented here. In part II the minimum emittance of the FODO achromat has been derived in a semianalytical approach. It has been shown, that after performing two optimization steps, the emittance can be reduced far below the minimum emittance of a pure FODO structure. In part III, three examples of the FODO achromat lattices for the ALS are presented. For the relatively short structure of the ALS, the minimum emittance unfortunately cannot be utilized because the strong focusing produces large chromatic aberrations which must be compensated with sextupoles of high strengths. These sextupoles generate geometric aberrations which reduce the dynamic acceptance below the acceptable limit. Therefore the FODO structures presented in part III are a compromise between the conflicting requirements of small emittance and large dynamic acceptance