BNL, Upton, Long Island, New York, USA
Most lattice correction algorithms, such as LOCO, rely on the amplitude of the BPM signals. However, these signals are a mixture of the BPM gain and beta-beat. Even though BPM gain can be fitted by analyzing the statistics of all the BPMs in a ring accelerator, we found the uncertainty is on the order of a few percent. On the other hand, the betatron phase advance, which is obtained from the correlation of two adjacent BPMs, is independent of the BPM gain and tilt error. It was found at NSLS-II that the measurement precision of the phase advance is typically 0.001 radian, which corresponds to about 0.2% of beta beat. The phase error can be corrected similarly using a response matrix, and at NSLS-II the phase error can be corrected to <0.005 radian (p-p) in less than half an hour. The same technique can be applied to the nonlinear lattice. By comparing the phase advance differences between the on- and off- orbit lattices, the sextupole strength error can be identified. Simulation and experimental results will be demonstrated in the paper.
