2002 Nonlinear Optics Measurements and Modelling for the CERN SPS

In 2002, nonlinear chromaticity, coupling, amplitude-dependent detuning, chromatic phase advance, resonance driving terms, and off-energy orbits were measured in the CERN SPS at 26 GeV/c. The optics model has been updated by adjusting the strengths of nonlinear field errors in the dipoles and quadrupoles, so as to reproduce the measured nonlinear chromaticity. We compare the field errors deduced in 2002, measuring over a larger momentum range, with those found in 2001 and 2000. The resolution is improved by averaging over all turn-by-turn position monitors in the ring instead of using a single dedicated pick up ('tune meter'). Computations using two different optics codes, MAD and SAD, indicate the sensitivity to matching algorithm and magnet representation. To validate the nonlinear optics model, the predicted tune shifts with transverse amplitude, driving terms of low-order resonance, etc., are compared with direct measurements.