Simultaneous Orbit Correction of Two Separate LHC Beams Sharing Common Elements

In the LHC the two beams share common elements near the crossing points of the machine. Since the two counter-rotating beams have the same sign of the charge, a magnet has a different effect on the two beams, which must be taken into account during the design process. This is also the case for orbit distortions originating from these common parts, e.g. disaligned common quadrupoles, and the orbit correctors in these areas. Any orbit corrector has a different effect on the two beams and cannot be used in a correction algorithm for a single beam only since it may have unwanted effects on the other beam.The existing closed orbit correction program COCU for SPS and LEP was modified to allow the simultaneous correction of both LHC beams, using the common correction dipoles as a single correction element but with a different response to the two beams

Implementation of new closed orbit correction procedures in the MAD-X program

The possibility to correct a closed orbit is a basic functionality in the MAD program. During the rewrite leading to the MAD-X version, the closed orbit correction procedures have been completely re-written and substantially extended. Additional algorithms have been added and problems with existing algorithms have been solved. Furthermore, new options allow more sophisticated studies and better control of the correction procedures. In this note I shall describe these new features and their raison d'etre. Most new features are the result of the immediate needs emerging from the extensive use of the program in realistic simulations. Some features which were practically never used have been dropped

Features and implications of different LHC crossing schemes

To avoid unwanted beam-beam interactions, the two LHC beams cross at an angle in all experimental interaction points. The choice of the crossing plane in the different areas has fundamental consequences on the effects of the long range beam-beam interaction. Recent changes to the hardware, i.e. introduction of a beam screen into the triplet quadrupoles, may limit this choice or reduce the flexibility. The consequences of different crossing scenarios are presented in this report. Other implications such as limitations to the correction possibilities and the flexibility of the crossing geometry are addressed

Consequences of Periodicity and Symmetry for the Beam-Beam Effects in the LHC

The beam-beam interactions in the LHC can be the driving force for non-linear resonances. These interactions are localized around the interaction point and therefore have periodic components which can suppress or enhance certain resonances. This has been analysed by studying the harmonic decomposition of the beam-beam interactions, taking into account both effects, i.e. long range and head on interactions. The consequences of symmetry breaking effects such as phase advance errors have also been studied

Summary of the Workshop on Beam-Beam effects in Large Hadron Colliders (LHC99)

The beam-beam interaction can limit the performance of hadron colliders such as the LHC and has to be taken into account during the design of the accelerator. A workshop was held at CERN from 12 to 16 April 1999 to review the current knowledge and experience and to discuss ongoing and future studies. The contributions and details of the discussion and the summaries are compiled in the proceedings of the workshop [1]. While these proceedings are a working document for further studies, this report intends to give an overview of the main problems and provides the interested but non-specialised reader with a survey of the critical issues, together with the proposed solutions and studies