A comparison of the Chasman-Green and triple bend achromat lattices
The basic Chasman-Green or double focusing achromat (DFA) lattice, see Fig. 1, represents the most compact and economical of the structures used in low emittance electron storage rings. The main problem with this structure arises from the requirement to operate at zero (or slightly positive) chromaticity. This demands the use of strong sextupole fields, which drive third order structure resonances. These, in turn, place a restriction on the tune of the lattice, particularly in the radial plane. Unfortunately, the DFA structure, which, when operated in the low emittance mode has a fixed phase advance across the achromat, is not very flexible in this regard. We will show, for example, that it is not possible to design for high-beta insertions while maintaining the desired tune. The triple bend achromat (TBA) structure utilizing combined function magnets, see Fig. 2, first described by Vignola as a candidate for the U.S. 6 GeV synchrotron radiation source, is the logical extension of the DFA lattice. Adding an extra bending magnet within the achromat permits the designer to tailor the phase advance across the achromat and the beta value in the insertion region while maintaining the desired tune shift across the cell. This paper details the difficulties with the DFA structure and shows how they are overcome in the TBA design. The principles are illustrated in two lattices which have been optimized for a 1.5 GeV synchrotron light source.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- Accelerator& Fusion Research Division
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 1000344
- Report Number(s):
- LBL-21279; TRN: US201024%%391
- Journal Information:
- Particle Accelerators, Journal Name: Particle Accelerators
- Country of Publication:
- United States
- Language:
- English
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