| Paper |
Title |
Page |
| WEPKF008 |
A Strategy for Sampling of the Field Quality of the LHC Dipoles
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1606 |
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- L. Bottura, S.D. Fartoukh, V. Granata, E. Todesco
CERN, Geneva
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We have measured the magnetic field of a considerable fraction of the superconducting LHC main dipoles, of the order of 300 in warm conditions and 100 in cold conditions. All LHC dipoles will be measured in warm conditions at the manufacturers to steer the production inside the acceptance limits imposed by beam dynamics. Using the available data we analysed the distributions of the main field and higher order field errors in warm and cold conditions, as well as the distribution of the warm-to-cold correlation. Based on this analysis we predict the minimum number of magnets that should be measured in cold conditions in order to guarantee that (1) the production is controlled within the specified limits (2) the field is known to a sufficient level for a sound installation and (3) the uncertainty on the knowledge of the magnetic field of the LHC dipoles is small enough for the commissioning of the accelerator and to insure operation of the machine in any condition, including higher energy. The main outcome of this analysis is that cold measurements on a fraction of the order of one third of the total production, i.e. approximately 400 dipoles, will be sufficient to achieve the above objectives.
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| WEPKF009 |
A Scaling Law for Predicting Snap-back in Superconducting Accelerator Magnets
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1609 |
| |
- T. Pieloni, L. Bottura, S. Sanfilippo
CERN, Geneva
- G. Ambrosio, P. Bauer
Fermilab, Batavia, Illinois
- M. Haverkamp
METROLAB, Plan-les-Ouates
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The decay of the sextupole component in the bending dipoles during injection and the subsequent snap-back at particle acceleration are issues of common concern, albeit at different levels of criticality, for all superconducting colliders built (Tevatron, HERA, RHIC) or in construction (LHC) to date. The main difficulty is the correction of the relatively large and fast sextupole change during snap-back. Motivated by the above considerations, we have conducted an extended study of sextupole snap-back on two different magnet families, the Tevatron and the LHC bending dipoles, using the same measurement method. We show in this paper that it is possible to generalise all the results obtained by using a simple, exponential scaling law. Furthermore, we show that for magnets of the same family the parameters of the scaling law correlate linearly. This finding could be exploited during accelerator operation to produce accurate forecast of the snap-back correction based solely on beam-based measurements.
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| WEPKF014 |
Magnetic Field Tracking Experiments for LHC
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1621 |
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- V. Granata, J. Billan, F. Bordry, L. Bottura, P. Coutinho Ferreira, E. Effinger, G. Fernqvist, P. Galbraith, Q. King, J. Pett, A. Raimondo, A. Rijllart, H. Thiesen
CERN, Geneva
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At the Large Hadron Collider (LHC) at CERN one of the fundamental requirements during the energy ramp is that the ratio between the field produced by the quadrupoles and the field in the dipoles remains constant in order to minimize the variation of the betatron tune that could induce particle loss. With a series of tracking experiments it has been demonstrated that this ratio can be maintained constant to better than 10-4 throughout the same current ramp as foreseen for the LHC. A technique has been developed to optimise the dipole and quadrupole current ramps to obtain the required ratio of B2/B1. Measurements performed by modulating the current with a harmonic function (so-called k-modulation) demonstrated that it is possible to modulate the strength of an individual quadrupole to determine the magnetic center through beam-based measurements.
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