Chromatic coupling correction in the Large Hadron Collider

Abstract

In this article we present the measurement and correction of the chromatic coupling in the LHC. The transverse coupling is calculated from turn-by-turn data, exciting the beam with an ac dipole. By adjusting the momentum relative to the reference energy and repeating the measurement, we obtain the transverse coupling dependency on momentum. The measurements are compared to the predictions from the magnetic model, and show good agreement. We describe the algorithm used to calculate the corrections, which are performed using skew sextupoles in the LHC lattice. A reduction in the chromatic coupling of a factor 2.5±0.4 for beam 1 and 1.6 ±0.3 for beam 2 was obtained after applying the corrections.