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Paper Title: Model Independent Analysis (MIA) for linear optics verification
Primary Author: Y.T. Yan
Institution: SLAC
Secondary Authors and Institutions: Y. Cai, J. Irwin, M. Sullivan
Working Groups IR (background, magnets) & Optics
The principal goal of MIA is to exploit underlying correlations in BPM measurements to improve beam position determination and provide information on machine component performance. Currently, these techniques are being applied to the PEP-II rings to better determine its linear optics. We start with buffering two sets of about 2000 turns of BPM data for a beam resonantly excited at the horizontal and vertical tunes. Two pairs of linearly independent transverse orbits are obtained with a resolution enhanced by FFT filtering. The enhanced orbits may be used to calculate phase advances, betatron amplitudes and local "Green's function" matrix elements (R12, R34, R14, R32) between BPMs. The Green's function element measurement can be compared with predictions from the machine model. Taking all BPM gains and couplings, normal and skew quadrupole strengths, and sextupole misalignments as variables, we use an SVD-enhanced least-square fitting to infer the difference between the machine and the model lattice. The method yields a set of proposed adjustments to the machine to bring it into conformance with the model.