Measurement and Scaling Laws of the Sextupole Component in the LHC Dipole Magnets

One of the main requirements for the magnet operation of the Large Hadron Collider at CERN is the correction of the dynamic multipole errors produced. In particular, integrated sextupole errors in the main dipoles must be kept well below 0.1 units to ensure acceptable chromaticity. The feed-forward control of the LHC magnets is based on the Field Description for the LHC (FiDeL), a semi-empirical mathematical model capable of forecasting the magnet’s behaviours in order to suitably power the corrector scheme. Measurement campaign were recently undertaken to validate the model making use of a novel Fast rotating-coil Magnetic Measurement Equipment (FAME), able to detect superconductor decay and snapback transient with unprecedented accuracy and temporal resolution. We discuss in this paper the test setup and some measurement results confirming the FiDeL model.