Lattice comparison for the synchrotron light source BESSY II

A study of three different lattice schemes was done to find out an appropriate solution for the BESSY II lattice. Simple arrangements of achromatic bends like the two or three dipole scheme were considered. To compare different arrangements studies were made of: (1) a tenfold triple-bend achromat lattice (TBA10) with a triplet matching the insertion section to the achromat; (2) a twelvefold triple-bend achromat (TBA12) with a doublet as a matching section; and (3) a fourteen fold double-bend achromat (DBA14) with a triplet as a matching section. It is concluded that the different optics studied for BESSY II are all sufficiently well within the specifications and are all feasible. BESSY II will be optimized for insertion devices; this favors a higher periodicity. However, the advantage of the TBA lattices compared to the DBA is the better performance of the dipole radiation. The larger number of straight sections of the DBA14 has to be further weighted by the fact that half of them are reduced in length. The TBA10 better satisfies the required beam specifications and shows more flexibility in compensating the linear effects of the insertion elements. It also offers more space for diagnostics and correction elements. However, the behavior with respect to off-momentum particles of the TBA10 is not quite as good as that of the TBA12 type. In addition, the closed orbit of the TBA 10 lattice is more sensitive to focusing and alignment errors than the TBA12. A relaxed TBA10 with less focusing strength and a larger emittance might overcome these problems.<
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