Precise determination and comparison of the SPS dynamic aperture in experiment and simulation

The combined effect of nonlinear fields and tune ripple can lead to chaotic motion and particle loss in proton accelerators thereby limiting the dynamic aperture of these machines. The SPS Dynamic Aperture Experiment is performed to study a controlled nonlinear machine under the influence of power supply ripple. To this end eight strong sextupoles are used to make the SPS nonlinear. The tune ripple is introduced with one special quadrupole which allows to vary the ripple frequency and depth. In parallel long-term element-by-element tracking is done to investigate its applicability for the estimation of the dynamic aperture of a real accelerator. The influence of nonlinear magnetic fields and tune ripple is observed at two working points using a flying wire of 8 μm diameter. The experimentally determined dynamic aperture is compared with survival plots obtained from the tracking and their differences are discussed