Paper |
Title |
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WEPAB006 |
Performance Improvements of the BESSY II Storage Ring by Optimizing the Phase Acceptance |
2571 |
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- P. Kuske, J. Li
HZB, Berlin, Germany
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Linear optics modifications in order to improve injec-tion efficiency and for the installation of two IDs in one straight section demand an optimization of the sextupole correction scheme. Four harmonic sextupole families were sufficient with the earlier 8-fold symmetric lattice. Today there are ten families of harmonic sextupole mag-nets in addition to the three families of chromatic sextu-poles. This paper describes our experimental approach to find better settings for these harmonic sextupoles based on the direct optimization of the injection efficiency with a longitudinal phase offset between storage ring and the injector - in our case a booster synchrotron. As demon-strated in the paper, the resulting improvement of the phase acceptance of the ring leads to increased momen-tum acceptance by suppressing 3rd order non-systematic resonances. This increases not only the injection effi-ciency for long bunches but also the Touschek lifetime, the largest contribution to the overall lifetime of low emittance storage rings.
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DOI • |
reference for this paper
※ https://doi.org/10.18429/JACoW-IPAC2017-WEPAB006
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THPAB007 |
Short Bunches at the Transition From Strong to Weak Longitudinal Instability |
3696 |
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- P. Kuske
HZB, Berlin, Germany
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The interaction of particles with their vacuum sur-roundings can lead to longitudinal instabilities of the whole bunch of particles. Most of these instabilities are strong and the growth rates are large compared to the damping rate. For a weak instability the opposite is true and with just a resistive impedance the instability would always be weak and independent of the bunch length. The interaction of a bunch with its own radiation emitted midway between parallel plates leads to a strong instabil-ity for long bunches and a transition to weak instability if the bunch length becomes shorter. This regime is ana-lysed numerically with a Vlasov-Fokker-Planck solver. The results are compared to recent observations at ANKA. An attempt is made to explain the remaining discrepan-cies by including higher order terms of the momentum compaction factor into these calculations. There are indi-cations that the simple model needs refinements in order to take radiation from upstream dipoles into account.
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DOI • |
reference for this paper
※ https://doi.org/10.18429/JACoW-IPAC2017-THPAB007
|
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Export • |
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※ LaTeX,
※ Text/Word,
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