Fast and precise technique for magnet lattice correction via sine-wave excitation of fast correctors

A novel technique has been developed to improve the precision and shorten the measurement time of the LOCO (linear optics from closed orbits) method. This technique, named AC LOCO, is based on sine-wave (ac) beam excitation via fast correctors. Such fast correctors are typically installed at synchrotron light sources for the fast orbit feedback. The beam oscillations are measured by beam position monitors. The narrow band used for the beam excitation and measurement not only allows us to suppress effectively the beam position noise but also opens the opportunity for simultaneously exciting multiple correctors at different frequencies (multifrequency mode). We demonstrated at NSLS-II that AC LOCO provides better lattice corrections and works much faster than the traditional LOCO method.

Figure 1

The maximum power supply amplitude as a function of frequency.

Figure 2

Small-signal frequency response functions: horizontal (blue) and vertical (red).

Figure 3

Example of PSD spectrum of a horizontal BPM (left); example of beam oscillation spectrum (right).

Figure 4

Measured single-to-noise ratio vs frequency: horizontal (blue) and vertical (red).

Figure 5

Root mean square amplitude errors at 20 Hz.

Figure 6

Amplitudes measured by all BPMs at 20 Hz: horizontal (left) and vertical (right).

Figure 7

Spectra of fast corrector excitation signals.

Figure 8

Amplitude spectra of horizontal (blue) and vertical (red) BPM signals.

Figure 9

Convergence of beta function: horizontal (left) and vertical (right).

Figure 10

Convergence of dispersion: horizontal (left) and vertical (right).