An ultra-low emittance damping ring lattice and its dynamic aperture

A few of the problems in the design of an ultra-low-emittance damping ring are considered. It is pointed out that once the goals of low emittance and fast damping times are achieved in the linear lattice design, there remains the serious problem of the nonlinear beam dynamics. Low-emittance lattices usually have a small dynamic aperature due to the particularly strong sextupoles necessitated by the small average dispersion function. The dynamic aperature solution is to abandon the conventional interleaved sextupole scheme and to place sextupoles in pairs 180° apart in betatron phase with no other sextupoles in between. The deleterious effect of the sextupole thickness can be partially corrected by octupolar fields