An active alignment test facility for the CERN linear collider

It is noted that the accelerating and focusing structure of the CERN high-energy linear collider must be aligned and maintained in the transverse plane to very tight tolerances (5 mu m for the accelerating sections and 1 mu m for the quadrupoles) to avoid excessive beam blow-up due to beam-induced transverse wake fields. Since normal ground motion produces displacements which exceed these tolerances, a dynamic alignment system using beam-derived signals from beam position monitors to drive precision micromovers under closed-loop control to maintain the components in position is foreseen. A remote computer-controlled micro-movement test facility has been constructed at CERN to study the various problems associated with such systems. The behavior of a string of 40 2.5-m-long girders using this prealignment system has been simulated using an existing CERN geodesic compensation program.<>