| 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. |