Study of Modified Sextupoles for Dynamic Aperture Improvement in Synchrotron Radiation Sources*

The possibility of increasing the dynamic aperture in high brilliance synchrotron radiation sources by shaping the field of the chromaticity correction sextupoles is discussed. A new type of chromaticity correction magnets (“modified sextupoles”) is proposed, having the property of behaving like sextupoles near the magnetic axis, and more linearly at larger distances. It is shown that a large increase of dynamic aperture is achievable with this method. The off-momentum behavior is discussed in terms of chromatic properties and dynamic aperture. Several types of field shape are considered. The technique for designing such magnets is presented, together with an example of magnets that give the required field distribution.