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arXiv · 2406.16660

Dedicated beam position monitor pair for model-independent lattice characterization at NSLS-II

Yongjun Li·Kiman Ha·Danny Padrazo·Bernard Kosciuk·Belkacem Bacha·Michael Seegitz·Robert Rainer·Joseph Mead·Xi Yang·Yuke Tian·Robert Todd·Victor Smaluk·Weixing Cheng
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Abstract

This paper reports recent lattice characterization results obtained at the National Synchrotron Light Source II (NSLS-II) storage ring, conducted without reliance on a lattice model. A pair of beam position monitors (BPMs) with bunch-by-bunch (B$\times$B) resolution, were recently installed in a section of the storage ring free of magnetic fields. The new BPM pair measured the beam, or bunch's transverse Poincar\'e map precisely after the beam was excited. Linear one-turn-matrices (OTM) were then derived, and from these, the 4-dimensional coupled Twiss parameters were extracted at the locations of the BPM pair. By normalizing beam oscillation amplitudes with the Twiss parameters, the global action-variables were obtained. These action-variables facilitated the measurement of the local Twiss parameters observed by other BPMs independent on lattice model. This method is general, and particularly useful in certain scenarios such as a round beam mode in a diffraction-limited light source ring. We applied it to assess both weakly and strongly coupled lattices at the NSLS-II ring. Through analysis of the strongly coupled lattice, the quadrupole tilt errors were estimated to be less than 400 \si{\mu}rad. Utilizing the BPMs' B$\times$B resolution, for the first time we observed the variations of the linear lattice along a long bunch-train.

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Yongjun Li, Kiman Ha, Danny Padrazo, Bernard Kosciuk, Belkacem Bacha, Michael Seegitz, Robert Rainer, Joseph Mead, Xi Yang, Yuke Tian, Robert Todd, Victor Smaluk, Weixing Cheng. 2024-06-24. Dedicated beam position monitor pair for model-independent lattice characterization at NSLS-II. https://doi.org/10.1016/j.nima.2024.169557

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