CERN, Geneva
The start-up of the LHC has provided the first field test for the concept, functionality and accuracy of FiDeL, the Field Description for the LHC. FiDeL is primarily a parametric model of the transfer function of the main field integrals generated by the series of magnets in the LHC powering circuits, from main optical elements to high-order harmonic correctors, both superconducting and normal-conducting magnets. In addition, the same framework is used to predict harmonic errors of both static and dynamic nature, and forecast appropriate corrections. In this paper we give a description of the level of detail achieved in the model and the rationale adopted for the LHC start-up. Beam-based measurements have been used for an assessment of the first-shot accuracy in the prediction of the current setting for the main arc magnets*.
*The work reported has been performed by the authors and the FiDeL Team
CERN, Geneva
The Large Hadron Collider (LHC) has been aligned using classical and non-standard techniques. The results have been seen on September 10th, 2008, the day when the beam made several turns in the machine with very few correctors activated. The paper will present the different steps of the alignment, from the metrological measurements done during the phase of the magnets assembly to the alignment itself in the tunnel as well as the techniques used to obtain the accuracy required by the physicists. The correlation of the results of this alignment with the position of the beam seen on the BPMs by the operation team during the days the beam has circulated will be presented.
CERN, Geneva
Until now, the continuous monitoring of the LHC lattice has been considered as impractical due to tight constraints on the maximum allowed beam excitations and acquisition time usually required for betatron function measurements. As an further exploitation of the Base-Band-Tune (BBQ) detection principle, already widely used for tune diagnostic, a real-time beta-beat measurement prototype has been successfully tested at the CERN SPS based on the continuous measurement of the cell-to-cell betatron phase advance. Tests show that the phase resolutions is better than a degree corresponding to a peak-to-peak beta-beat resolution of about one percent. Due to the system's high sensitivity it required only micro-metre range excitation, making it compatible with nominal LHC operation. This contribution discusses results, measurement systematics and possible additional exploitation that may be used to improve the nominal LHC performance.