Abstract
The vertical-beam emittance in an electron storage ring is mainly determined by two factors: the linear betatron coupling and the spurious vertical dispersion generated by magnet errors. We find that the contribution of spurious vertical dispersion is larger than that generated by the linear betatron coupling. Using the independent component analysis (ICA) method, we develop stop band corrections to reduce the vertical emittance. We demonstrate our method by making ICA and correction to a quadruple-bend achromatic low emittance lattice. Six families of skew quadrupoles can effectively minimize both the vertical dispersion and the linear betatron coupling.
Highlights
In recent years, many low emittance electron storage rings around 3 GeV beam energy have been proposed and constructed in the world
We find that the contribution of spurious vertical dispersion is larger than that generated by the linear betatron coupling
We demonstrate our method by making independent component analysis (ICA) and correction to a quadruple-bend achromatic low emittance lattice
Summary
Many low emittance electron storage rings around 3 GeV beam energy have been proposed and constructed in the world. The vertical-beam emittance in a storage ring arises essentially from the linear betatron coupling and the quantum fluctuation due to the vertical dispersion function as derived in Ref. Since a small vertical emittance is preferable in a high brilliance photon source, we need precise measurement and correction of betatron coupling and vertical dispersion function. We add white noise into the BPM data, and use the ICA method to extract spatial functions of all independent modes These spatial functions are called the derived betatron amplitude functions, dispersion functions, etc. The QBA has another advantage over the DB nonachromatic lattice that the correction of the linear betatron coupling will not affect the vertical dispersion function.
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