New approach to LHC optics commissioning for the nonlinear era

• Main Authors: E. H. Maclean, R. Tomás, F. S. Carlier, M. S. Camillocci, J. W. Dilly, J. Coello de Portugal, E. Fol, K. Fuchsberger, A. Garcia-Tabares Valdivieso, M. Giovannozzi, M. Hofer, L. Malina, T. H. B. Persson, P. K. Skowronski, A. Wegscheider
• Format: Article
• Language: English
• Published: American Physical Society 2019-06-01
• Series: Physical Review Accelerators and Beams
• Online Access: http://doi.org/10.1103/PhysRevAccelBeams.22.061004

In 2017, optics commissioning strategy for low-β^{*} operation of the CERN Large Hadron Collider (LHC) underwent a major revision. This was prompted by a need to extend the scope of beam-based commissioning at high energy, beyond the exclusively linear realm considered previously, and into the nonlinear regime. It also stemmed from a recognition that, due to operation with crossing angles in the experimental insertions, the linear and nonlinear optics quality were intrinsically linked through potentially significant feed-down at these locations. Following the usual linear optics commissioning therefore, corrections for (normal and skew) sextupole and (normal and skew) octupole errors in the high-luminosity insertions were implemented. For the first time, the LHC now operates at top energy with beam-based corrections for nonlinear dynamics, and for the effect of the crossing scheme on beta-beating and dispersion. The new commissioning procedure has improved the control of various linear and nonlinear characteristics of the LHC, yielding clear operational benefits.