DYNAMIC APERTURE EXPERIMENT AT A SYNCHROTRON

The dynamic aperture experiment at the CERN Super Proton Synchrotron ~SPS! was aimed at finding the relevant effects that limit single-particle stability in hadron storage rings. These effects were studied in the SPS and compared with long-term particle tracking to determine to what extent computer simulations can predict the dynamic aperture under well-known conditions. Such investigations are very important for future hadron colliders such as the Large Hadron Collider as the design of these machines relies heavily on simulations. Besides this practical goal it was of utmost interest to improve the phenomenological understanding of the intricate details of particle motion in phase space. This experiment was carried out by successive teams over a period of ten years. We summarize the techniques, results, and conclusions. @S1063-651X~97!10602-X# PACS number~s!: 29.20.2c All high-energy hadron accelerators currently planned or under construction need superconducting technology to reach the high fields needed to guide and focus the beams. Whereas in the classic technology the required fields were reproduced by accurately shaping the magnetic pole pieces, in superconducting magnets the field quality depends almost entirely on the position and properties of the superconducting filaments inside the coils. As a result it is more difficult to avoid unwanted multipolar errors that affect the particle dynamics @1,2#. Since hadrons lose a negligible part of their energy through synchrotron radiation, their motion in phase space can be adequately described in the framework of the Hamiltonian formalism. In such conservative systems, the nonlinearities can make the motion of the particles chaotic in parts of the phase space through which they slowly migrate outwards until they are lost at some obstacle in the beam pipe. It is of utmost importance for the design of a machine like the Large Hadron Collider ~LHC!, the 7 TeV on 7 TeV proton collider planned in the Large Electron-Positron ~LEP! tunnel at CERN, to understand in detail the nonlinear dynamics of the circulating particles. The main purpose of the dynamic aperture experiment at the Super Proton Synchrotron ~SPS! was therefore to simulate a nonlinear machine including tune modulation, which is known to enhance the destabilizing effects of nonlinearities @3#, and to investigate