| Paper |
Title |
Page |
| TUPC098 |
Results of the LHC Prototype Chromaticity Measurement System Studies in the CERN-SPS
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1290 |
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- R. J. Steinhagen, A. Boccardi, T. Bohl, M. Gasior, O. R. Jones, J. Wenninger
CERN, Geneva
- K. K. Kasinski
AGH, Cracow
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Tune and chromaticity control is an integral part of safe and reliable LHC operation. Tight tolerances on the maximum transverse beam excursions allow oscillation amplitudes of less than 30 um. This leaves only a small margin for transverse beam and momentum excitations required for measuring tune and chromaticity. This contribution discusses the baseline LHC continuous chromaticity measurement with results from tests at the CERN-SPS. The system is based on continuous tracking of the tune using a phase-locked-loop (PLL) while modulating the beam momentum. The high PLL tune resolution achieved ( ~1·10-6 ) made it possible to detect chromaticity changes well below the nominally required 1 unit for relative momentum modulations of only 2·10-5. The sensitive tune measurement front-end employed allowed the PLL excitation and radial amplitudes to be kept below a few tens of micrometers. These results show that this type of measurement can be considered as practically non-perturbative permitting its use even during nominal LHC operation.
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| TUPP067 |
Transverse Mode-coupling Instability in the CERN SPS: Comparing MOSES Analytical Calculations and HEADTAIL Simulations with Experiments in the SPS
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1694 |
| |
- B. Salvant
EPFL, Lausanne
- G. Arduini, E. Métral, G. Papotti, G. Rumolo, R. J. Steinhagen, R. Tomas
CERN, Geneva
- R. Calaga
BNL, Upton, Long Island, New York
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Since 2003, single bunches of protons with high intensity (1.2·1011 protons) and low longitudinal emittance (0.2 eVs) have been observed to suffer from heavy losses in less than one synchrotron period after injection at 26 GeV/c in the CERN Super Proton Synchrotron (SPS) when the vertical chromaticity is corrected. Understanding the mechanisms underlying this instability is crucial to assess the feasibility of an anticipated upgrade of the SPS, which requires bunches of 4·1011 protons. Analytical calculations from MOSES and macroparticle tracking simulations using HEADTAIL with an SPS transverse impedance modelled as a broadband resonator had already qualitatively and quantitatively agreed in predicting the intensity threshold of a fast instability. A sensitive frequency analysis of the HEADTAIL simulations output was then done using SUSSIX, and brought to light the fine structure of the mode spectrum of the bunch coherent motion. A coupling between the azimuthal modes -2 and -3 was clearly observed to be the reason for this fast instability. The aim of the present paper is to compare the HEADTAIL simulations with dedicated measurements performed in the SPS in 2007.
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