| Paper | Title | Page |
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| TUPFI028 | Beam Losses Through the LHC Operational Cycle in 2012 | 1400 |
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| We review the losses through the nominal LHC cycle for physics operation in 2012. The loss patterns are studied and categorized according to timescale, distribution, time in the cycle, which bunches are affected, whether coherent or incoherent. Possible causes and correlations are identified, e.g. to machine parameters or instability signatures. A comparison with losses in the previous years of operation is also shown. | ||
| TUPFI029 | Luminosity Lifetime at the LHC in 2012 Proton Physics Operation | 1403 |
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| In 2012, the LHC was operated at 4 TeV flat top energy with beam parameters that allowed exceeding a peak instantaneous luminosity of 7500 (ub*s)-1 and a total of 23 fb-1 integrated luminosity in the ATLAS and CMS experiments. This paper elaborates on the evolution of the LHC luminosity and luminosity lifetime during proton physics fills and through the year 2012. Bunch to bunch differences and the impact of different machine settings are highlighted. | ||
| TUPFI030 | LHC Machine Developments in 2011-12 | 1406 |
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| In 2011 and 2012 LHC machine development (MD) sessions were performed during dedicated slots of beam time. These MD studies were scheduled and planned well in advance. Study topics reflected the previously agreed priorities, such as further optimizing machine performance, exploring beam parameters beyond design targets, assessing machine limitations, testing new concepts and machine settings, preparing future LHC running in view of the 2013/14 LHC shutdown and the re-commissioning of the LHC at nominal beam energy in 2014/15. We describe the planning, preparation, execution, review, and documentation of these LHC beam studies and highlight some key results. | ||
| TUPFI031 | Effect of Collision Pattern in the LHC on the Beam Stability: Requirements from Experiments and Operational Considerations | 1409 |
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| Coherent instabilities of bunches in the LHC bunch train can be observed when the tune spread from beam-beam interactions becomes insufficient to ensure Landau damping. In particular these effects are seen on bunches with a reduced number of beam-beam interactions due to their collision pattern. Furthermore, such a reduction of the necessary stability can occur during the processes when the beams are prepared for collisions or during the optimization procedure. We discuss the observations and possible countermeasures, in particular alternatives to the existing beam manipulation processes where such a situation can occur. | ||
| TUPFI032 | Observation of Instabilities in the LHC due to Missing Head-on Beam-beam Interactions | 1412 |
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| We report the observation of coherent instabilities on individual bunches out of the LHC bunch train. These instabilities occured spontaneously after several hours of stable beam while in other cases they were related to the application of a small transverse beam separation during a luminosity optimization. Only few bunches were affected, depending on there collision scheme and following various tests we interprete these instabilities as a sudden loss of Landau damping when the tune spread from the beam-beam interaction became insufficient. | ||
| TUPFI034 | Observations of Two-beam Instabilities during the 2012 LHC Physics Run | 1418 |
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| During the 2012 run coherent beam instabilities have been observed in the LHC at 4 TeV, during the betatron squeeze and in collision for special filling patterns. Several studies to characterize these instabilities have been carried out during operation and in special dedicated experiments. In this paper we summarize the observations collected for different machine parameters and the present understanding of the origin of these instabilities. | ||
| TUPME060 | Tune Studies with Beam-Beam Effects in LHC | 1703 |
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Funding: This work was partially supported by the U.S. LARP and the NERSC of the U.S. Department of Energy under contract No. DE-AC02-05CH11231. In high brightness colliders, the tune spread due to the collisions has a significant impact on the quality of the beams. The impact of the working point on emittance growth and beam lifetime has been observed in beam experiments in LHC. Strong-strong beam-beam simulations that were accomplished to better understand such observations are shown. Compared to experiments, wide ranged parameter scans can be done easily. Tune footprints and scans of the emittance growth obtained from simulations are discussed. Three cases are considered: Very high intensity, moderate intensity and collisions with separated beams. |
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| TUPWO048 | Understanding the Tune, Coupling, and Chromaticity Dependence of the LHC on Landau Octupole Powering | 1976 |
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| During the 2012 LHC run there were several observations of unexpectedly large shifts to the tune, chromaticity, and coupling which were correlated with changes in the powering of Landau octupoles (MO). Understanding the chromaticity dependence is of particular importance given it's influence on instabilities. This paper summarizes the observations and our attempts to-date to understand the relationship between Q, Q', c- and the MO powering. | ||
| WEPEA071 | Performance Limitations in the Lhc Due to Parasitic Beam-Beam Encounters - Parameter Dependence, Scaling, and Pacman Effects | 2672 |
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| We studied possible limitations due to the long-range beam-beam effects in the LHC. With a large number of bunches and collisions in all interaction points, we have reduced the crossing angles (separation) to enhance long-range beam-beam effects to evaluate their influence on dynamic aperture and losses. Different β*, number of bunches and intensities have been used in several dedicated experiments and allow the test of the expected scaling laws. | ||