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Orbit bumps in sextupoles are routinely used for tuning the luminosity in the PEP-II B-Factory. Anti-symmetric bumps at a pair of identical sextupoles separated by –I section generate the net dispersion, while symmetric horizontal bumps induce a tune shift and beta beat. By combining two of these symmetric bumps with opposite signs, where the second pair is 90 ° away, the tune shift cancels and the beta beat doubles. In the low energy ring (LER), there are four –I sextupole pairs per arc, located one after another 90 ° apart, where pairs 1 and 3 are at the same phase and pairs 2 and 4 are 90 ° away. By making two symmetric bumps with opposite sign in pairs 1 and 3, the tune shift and beta beat outside this region cancel, but there is a local change of phase and beta in the 2 nd sextupole pair located in the middle. By using this bump knob, the LER lifetime improved by a factor of 3, losses by a factor of 5, and the beam-beam background in the drift chamber of the BaBar detector by 20%. Optics analysis showed that the local phase change at the 2 nd sextupole pair can compensate the 3 rd order chromaticity

Year: 2014

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