COMPARISON OF MEASURED AND COMPUTED DYNAMIC APERTURE FOR THE SPS AND THE HERA PROTON RING

Nonlinear magnetic fields in conjunction with tune modulation can lead to chaotic particle motion and thereby limit the dynamic aperture of hadron storage rings. This is of particular interest for the LHC at in jection energy where the geld errors of the superconducting magnets an d the beam size have their maximum. The SPS dynamic aperture experimen t was performed to study a controlled nonlinear machine under the infl uence of tune modulation. In parallel long-term tracking simulations w ere done to test to which extend computer programs can predict the dyn amic aperture under those conditions. In a complementary experiment at the HERA proton ring the dynamic aperture was measured at injection e nergy under normal operating conditions. The computer simulations for these measurements included a very detailed model of the nonlinear mag netic fields which were measured for each individual magnet.