Beam Threading in the LHC

Particles circulating in the LHC will experience a considerable amount of nonlinear magnetic forces, in particular at injection. Therefore it is important to show that a first circulating beam can be achieved at all, albeit in successive steps of measurement and correction. This has been done in simulation using a realistic model of the LHC which includes all estimated magnet alignment and field e rrors. The automatic procedure is based on pickups and corrector magnets. The results of this study have influenced the choice of the pickup system for the LHC. In particular, they show that a suffici ently smooth initial trajectory can be achieved even with a certain percentage of "dead" pickups.