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| MOPPC002 | Local Chromatic Correction Scheme and Crab-waist Collisions for an Ultra-low β* at the LHC | 118 |
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Funding: Work supported by the European Commission under the FP7 Research Infrastructures project Eu- CARD, grant agreement no. 227579. We discuss potential merits and the parameter range of interest for a possible crab-waist collision scheme at the LHC, and report preliminary optics studies of a local chromatic correction scheme with flat beams (βx*>>βy*), which could boost the LHC luminosity by about an order of magnitude and would also allow for crab-waist collisions. |
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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. | ||
| TUPPR022 | Traditional Final Focus System for CLIC | 1858 |
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| Next generation linear colliders needs a very strong focalisation to reach nanometer beam size at the Interaction Point. This task and the chromatic correction generated by the strong lenses is done by the Final Focus System. A traditional Final Focus System based on dedicated chromaticity correction sections is presented as an alternative for CLIC Final Focus. The scheme of the lattice is shown and some tolerances in the Final Doublet are calculated. A systematic tuning using Simplex algorithm and sextupole knobs is performed. The complete comparison to the Local Chromaticity correction scheme is presented. | ||
| TUPPR023 | Final-Focus Optics for the LHeC Electron Beam Line | 1861 |
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Funding: Work supported by the European Commission under the FP7 Research Infrastructures project Eu- CARD, grant agreement no. 227579. One of the options considered for the ECFA-CERN-NuPECC design study for a Large Hadron electron Collider (LHeC)* based on the LHC is adding a recirculating energy-recovery linac tangential to the LHC. First designs of the electron Final Focus System have shown the need to correct the chromatic aberrations. Two designs using different approaches for the chromaticity correction are compared, namely, the local chromaticity correction** and the traditional approach using dedicated sections. *LHeC Study Group, “A Large Hadron Electron Collider at CERN,” LHeC-Note 2011-001 (2011). **J. Abelleria et al., "Design Status of LHeC Linac‐Ring Interaction Region," IPAC2011, p. 2796 (2011). |
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| TUPPR027 | Study of Multipolar RF Kicks from the Main Deflecting Mode in Compact Crab Cavities for LHC | 1873 |
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| A crab cavity system is under design in the frame work of the High Luminosity LHC project. Due to transverse space constraints on one hand and the RF frequency requirements on the other hand, the design of the crab cavities has to be compact. This results in the crab cavity shape being far from axially symmetric and, as a consequence, higher order multipolar components of the main deflecting mode are non-zero. In this paper, multipolar RF kicks from the main deflecting mode have been calculated in the compact crab cavities for LHC. They are compared to the multipolar error in magnetic elements of LHC. The influence of the RF kicks on the beam dynamics has been investigated and possible acceptable tolerances are presented. | ||
| TUPPR060 | Detection of Ground Motion Effects on the Beam Trajectory at ATF2 | 1954 |
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| The ATF2 experiment is currently demonstrating the feasibility of the beam delivery system for the future linear collider. The tunning is very critical to obtain the nanometer vertical beam size at the interaction point and in the case of CLIC, ground motion effects on the beam must be corrected. In this respect, as a proof of principle of a ground motion feed forward, the ground motion effects on the beam trajectory are extracted from the beam position monitor readings. | ||
| TUPPR075 | Challenges for the Magnet System of LHeC | 1996 |
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| The main challenges for the normal conducting magnet system are the very compact, low field, and high precision magnets for the ring-ring option and their rapid installation in the crowded LHC tunnel. The superconducting triplet magnets require strong gradients for the protons in close vicinity of a field-free region for the electrons. The field requirements for the ring-ring option allow a number of different magnet designs using the well-proven Nb-Ti superconductor technology and making use of the cable development for the LHC. The separation distance between the electron and proton beams in Q1 requires a half-aperture quadrupole design to limit the overall synchrotron radiation power emitted by the bending of the electron beam. The requirements in terms of aperture and field gradient are more difficult to obtain for the Linac-Ring option. Consequently we present the limitations for the field gradient and septum size achievable with both Nb-Ti and Nb3Sn superconducting technologies. | ||
| WEEPPB014 | The Magnetic Model of the LHC during the 3.5 TeV Run | 2194 |
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| The magnetic model of the LHC is based on a fit of the magnetic measurements through equations that model the field components (geometric, saturation, persistent) at different currents. In this paper we will review the main results related to the magnetic model during the run of the LHC in 2010-2011: with a top energy of 3.5 TeV, all components of the model but the saturation are visible. We first give an estimate of the reproducibility of the main components and multipolar errors as they can be deduced from beam measurements, i.e. orbit, tune, chromaticity, beta beating and coupling. We then review the main results relative to the decay at injection plateau, dependence on powering history, and snapback at the beginning of the ramp for both tune and chromaticity. We discuss the precision obtained in tracking the magnets during the ramp, where the persistent current components gradually disappear. We conclude by presenting the behaviour of the quadrupoles model during the squeeze. A list of the major changes implemented during the operation together with what are considered as the main open issues is given. | ||
| TUPPC081 | First Experimental Observations from the LHC Dynamic Aperture Experiment | 1362 |
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| Following intensive numerical simulations to compute the dynamic aperture for the LHC in the design phase, the successful beam commissioning and the ensuing beam operations opened the possibility of performing beam measurements of the dynamics aperture. In this paper the experimental set-up and the first observations based on the few experimental sessions performed will be presented and discussed in detail. | ||
| 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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| THPPP007 | Proton-Beam Emittance Growth in SPS Coasts | 3737 |
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Funding: This work partially supported by the US Department of Energy through the US LHC Accelerator Research Program (LARP). Proton-beam transverse emittance growth rates have been measured during SPS coasts to assess the possibility of using the SPS as a testbed for the LHC prototype crab cavities. The SPS measurements in coasts were performed at different beam energies, for varying RF voltage, beam intensity, and chromaticity. Results from these measurements are presented with potential explanations for the observed emittance growth. |
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