| Paper | Title | Page |
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| MOPPC003 | Very Fast LHC Crab Cavity Failures and their Mitigation | 121 |
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For the high-luminosity LHC upgrade program (HL-LHC), the installation of crab cavities (CCs) is needed to compensate the geometric luminosity loss due to the crossing angle and for luminosity leveling [*]. The baseline is a local scheme with CCs around the ATLAS and CMS experiments. In a failure case (e.g. a control failure or arcing in the coupler), the voltage and/or phase of a CC can change significantly with a very fast time constant of the order of 1 to 10 LHC turns. This can lead to large, global betatron oscillations of the beam. The impact of CC failures on the beam dynamics is discussed and the results from dedicated simulations are presented. Mitigation strategies to limit the impact of CC failures to an acceptable level are proposed.
* F. Zimmermann and O. Brüning, “Parameter Space for the LHC High-Luminosity Upgrade”, IPAC'12, MOPPC005, May 2012. |
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| MOPPC006 | 90m Optics Studies and Operation in the LHC | 130 |
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| A high β* = 90 m optics was commissioned and used for first very forward physics operation in the LHC in 2011. The experience gained from working with this optics in 5 studies and operation periods in 2011 was very positive. The target β* = 90 m was reached by a de-squeeze from the standard 11 m injection and ramp optics on the first attempt and collisions and first physics results obtained in the second study. The optics was measured and corrected with good precision. The running conditions were very clean and allowed for measurements with roman pots very close to the beam. | ||
| MOPPC016 | Combined Ramp and Squeeze at the Large Hadron Collider | 157 |
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| In the first two years of operation of the CERN Large Hadron Collider (LHC), the betatron squeeze has been carried out at constant flat top energy of 3.5 TeV. Squeeze setting functions are separated from the energy ramp functions. This ensured a maximum flexibility during commissioning because stopping at all intermediate optics for detailed measurements was possible. In order to then improve the efficiency of the operational cycle, combining the ramp and squeeze has been considered. In this paper, the various possibilities for this scheme are reviewed, and proposals of optimized operational cycles with combined ramp and squeeze are presented for different energies. Results of beam tests are also discussed. | ||
| MOPPC017 | Causes and Solutions for Emittance Blow-Up During the LHC Cycle | 160 |
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| Emittance measurements during the run 2011 indicated a blow-up of 20 % to 30 % from LHC injection to collisions. At the LHC design stage the total allowed emittance increase through the cycle was set to 7 %. One of the goals of the 2012 LHC run is therefore to understand and counteract the blow-up. Emittance growth measurements through the LHC cycle along with correlations with possible sources are presented in this paper. Solutions are proposed where possible. The emittance determination accuracy relies on the knowledge of the beam optics and on the present performance of the transverse profile monitors. Possible improvements of the diagnostics and of the related data analysis are also discussed. | ||
| MOPPD062 | Aperture Measurements in the LHC Interaction Regions | 508 |
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| The aperture of the LHC interaction regions is crucial for the LHC performance because it determines the smaller β* that can be achieved. The aperture has been measured at a maximum energy of 3.5 TeV and at different β* values, following optimized procedure to allow safe measurements at high energy. In this paper, the results of these aperture measurements, which are used as a reference for β* reach and crossing scheme estimates at the LHC interaction points, are presented. | ||
| TUPPR068 | The Achromatic Telescopic Squeezing Scheme: Basic Principles and First Demonstration at the LHC | 1978 |
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The Achromatic Telescopic Squeezing (ATS) scheme [1] is a novel squeezing mechanism enabling the production of very low β* in circular colliders. The basic principles of the ATS scheme will be reviewed together with its strong justification for the High-Luminosity LHC Project. In this context, a few dedicated beam experiments were meticulously prepared and took place at the LHC in 2011. The results obtained will be highlighted, demonstrating already the potential of the ATS scheme for any upgrade project relying on a strong reduction of β*.
[1] S. Fartoukh, "An Achromatic Telescopic Squeezing (ATS) Scheme For The LHC Upgrade," IPAC'11, WEPC037, p. 2088 (2001). |
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| THPPP010 | LHC Orbit Correction Reproducibility and Related Machine Protection | 3746 |
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| The Large Hadron Collider (LHC) has an unprecedented nominal stored beam energy of up to 362 MJ per beam. In order to ensure an adequate machine protection by the collimation system, a high reproducibility of the beam position at collimators and special elements like the final focus quadrupoles is essential. This is realized by a combination of manual orbit corrections, feed forward and real time feedback. In order to protect the LHC against inconsistent orbit corrections, which could put the machine in a vulnerable state, a novel software-based interlock system for orbit corrector currents was developed. In this paper, the principle of the new interlock system is described and the reproducibility of the LHC orbit correction is discussed against the background of this system. | ||
| THPPP018 | Operation of the LHC at High Luminosity and High Stored Energy | 3767 |
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| In 2011 the operation of the Large Hadron Collider LHC entered its first year of high luminosity production at a beam energy of 3.5 TeV. In the first months of 2011 the number of bunches was progressively increased to 1380, followed by a reduction of the transverse emittance, an increase of the bunch population and a reduction of the betatron function at the collision points. The performance improvements steps that were accumulated in 2011 eventually brought the peak luminosity to 3.6·1033 cm-2s−1. The integrated luminosity delivered to each of the high luminosity experiments amounted to 5.6 fb-1, a factor of 5 above the initial target defined in 2010. The operational experience with high intensity and high luminosity at the LHC will be presented here, together with the issues that had to be tackled on the road to high intensity and luminosity. | ||
| THPPR040 | First Operational Experience with the LHC Machine Protection System when Operating with Beam Energies Beyond the 100 MJ Range | 4062 |
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| The LHC made a remarkable progress in luminosity production during 2011 operation. This was made possible by a progressive increase of beam intensities by more than 5 orders of magnitude, reaching stored beam energies beyond 100MJ at the end of the year. The correct functioning of the machine protection systems was vital during initial operation and even more when approaching nominal beam parameters, where an uncontrolled loss of a small fraction of the beam is already sufficient to damage accelerator equipment or the large experimental detectors The machine protection system depends on the interplay of many different elements: beam dumping system, beam interlocks, beam instrumentation, equipment monitoring, collimators and absorbers, etc. The strategy applied during 2011 to allow for an efficient but yet safe increase of the beam intensities is presented along with the associated risks and drawbacks of a too aggressive approach. The experience gained with the key systems will be discussed along with possibilities to further enhance machine availability whilst maintaining the current level of safety. | ||
| THPPP012 | Performance of the CERN Heavy Ion Production Complex | 3752 |
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| The second LHC ion run took place at 1.38 A TeV/c per beam in autumn 2011; more than 100 inverse microbarns was accumulated by each of the experiments. In addition, the LHC injector chain delivered primary Pb and secondary Be ion beams to fixed target experiments in the North Area. This paper presents the current performance of the heavy ion production complex, and prospects to further improve it in the near future. | ||
| THPPP086 | UFOs in the LHC: Observations, Studies and Extrapolations | 3936 |
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| Unidentified falling objects (UFOs) are potentially a major luminosity limitation for nominal LHC operation. They are presumably micrometer sized dust particles which lead to fast beam losses when they interact with the beam. With large-scale increases and optimizations of the beam loss monitor (BLM) thresholds, their impact on LHC availability was mitigated from mid 2011 onwards. For higher beam energy and lower magnet quench limits, the problem is expected to be considerably worse, though. In 2011/12, the diagnostics for UFO events were significantly improved: dedicated experiments and measurements in the LHC and in the laboratory were made and complemented by FLUKA simulations and theoretical studies. The state of knowledge, extrapolations for nominal LHC operation and mitigation strategies are presented. | ||