Optics-measurement-based beam position monitor calibrations in the LHC insertion regions

摘要

Accurate measurements of optics functions, β , α , D, are essential for proper operation of a synchrotron both for machine protection and for performance. β functions can be obtained from different observables: phase and amplitude of the transverse betatron oscillations and change of the tune by modulating the current of quadrupoles (K-modulation). Reconstruction of β function using the betatron phase, in combination with K-modulation, has been the main measurement approach in the LHC IRs. Nonetheless, challenges have appeared in the β calculation using these two techniques when aiming for smaller β * , i.e., β -values at the interaction point (IP) in the LHC and the HL-LHC. The third β measurement technique, based on the beam position monitor (BPM) signal amplitude, has not been used as widely in the LHC as the other methods since it requires accurate BPM gain calibration. This paper presents the development of a technique based on optics measurements to calibrate accurately LHC IR BPMs, allowing to use of the amplitude information in the measurement of IR β functions.