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| MOPPC001 | Simulation of electron-cloud heat load for the cold arcs of the large hadron collider | 115 |
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| The heat load due to the electron cloud in the Large Hadron Collider (LHC) cold arcs is a concern for its performance near and beyond nominal beam current. We report the results of simulation studies, which examine the electron-cloud induced heat load for different values of low-energy electron reflectivity and secondary emission yield at injection energy, as well as at beam energies of 4 TeV and 7 TeV, for two different bunch spacing: 25 ns and 50 ns. Benchmarking the simulations against heat-load observations at different beam energies and bunch spacing allows an estimate of the secondary emission yield in the cold arcs of the LHC and of its evolution as a function of time. | ||
| 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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| MOPPC005 | Parameter Space for the LHC Luminosity Upgrade* | 127 |
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Funding: Work supported by the European Commission under the FP7 Research Infrastructures projects EuCARD, grant agreement no. 227579, and HiLumi LHC, grant agreement no. 284404. We review the parameter space for the high-luminosity upgrade of the LHC (HL-LHC). Starting from the luminosity targets and the primary limitations, e.g., long-range beam-beam effects, event pile up, electron cloud, turnaround time, intrabeam scattering, we determine the range for compatible beam parameters such as the beam intensity, bunch spacing, transverse and longitudinal emittances, bunch length, and IP beta functions required to meet the HL-LHC goals. A selection of a few possible parameter sets is presented for comparison and discussion. |
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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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| MOPPP004 | Further Study on Fast Cooling in Compton Storage Rings | 571 |
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| Compton sources can produce gamma-ray photons of ultimate intensity, but suffer from the large recoils experienced by the circulating electrons scattering off the laser photons. We have previously proposed a scheme called asymmetric fast cooling to reduce the beam energy spread in Compton rings. This report presents results of further studies on the fast cooling. In particular, we show that (1) a proper asymmetric setup of the scattering point results in significant reduction of the quantum losses of electrons in Compton rings with moderate energy acceptance, and (2) the optimized pulsed mode of operation in synchrotron-dominated rings enhances the overall performance of such gamma-ray sources. Theoretical results presented are in good accordance with numerical simulations. We discuss the performance of an existing storage ring such as KEK ATF DR equipped with an optical cavity and presently available laser system. | ||
| 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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| 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. | ||
| TUPPR076 | The LHeC Project Development Beyond 2012 | 1999 |
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| The LHeC study group is finalizing a Conceptual Design Report for publication early in 2012. This paper discusses the next steps required for developing a Technical Design Report and highlights the R&D developments, test facilities and implementation studies that need to be addressed over the coming years. Particular emphasize will be given to similarities with other ongoing accelerator and detector studies, and to a discussion of possible international collaboration efforts. | ||
| TUPPR077 | Simulation Studies for the LHC Long-Range Beam-Beam Compensators | 2002 |
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| The LHC performance and the minimum crossing angle are limited by long-range beam-beam collisions. Wire compensators can mitigate part of the long-range effects and may allow for smaller crossing angles, smaller β*, or higher beam intensity. A prototype long-range wire compensator should be installed in the LHC by 2014/15. We report simulation studies examining and comparing the efficiency of the wire compensation, in terms of tune footprint or dynamic aperture, at various candidate locations, with different wire shapes, and for varying transverse distance from the beam. | ||
| TUPPR078 | LEP3: A High Luminosity e+e− Collider in the LHC Tunnel to Study the Higgs Boson | 2005 |
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| Recent indications from two LHC experiments suggest that the Higgs boson might be light, within the mass range 115-130 GeV. Such object could be studied at an e+e− collider with about 240 GeV centre-of-mass energy. A corresponding Higgs factory – “LEP3” - could be installed in the LHC tunnel, reducing its cost and also allowing for a second life of the two LHC general-purpose detectors. We present preliminary accelerator and beam parameters for LEP3 tailored so as to provide a peak luminosity of 1034/cm2/s at each of two experiments, while respecting a number of constraints including beamstrahlung limits. At this luminosity around 20,000 Higgs events per year per experiment could be obtained for a Standard Model Higgs boson with a mass of 115-130 GeV. For the parameters considered the estimated luminosity lifetime is about 12 minutes, and the synchrotron radiation losses are 50 MW per beam. High operational efficiency requires two rings: a low emittance collider storage ring operating at constant energy, and a separate accelerator to top up the colliding beams every few minutes. The alternative of a larger ring collider installed in a new, bigger tunnel will also be discussed. | ||
| TUPPC086 | Conceptual Design of the CLIC damping rings | 1368 |
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| The CLIC damping rings are designed to produce unprecedentedly low-emittances of 500 nm and 5 nm normalized at 2.86 GeV, in all beam dimensions with high bunch charge, necessary for the performance of the collider. The large beam brightness triggers a number of beam dynamics and technical challenges. Ring parameters such as energy, circumference, lattice, momentum compaction, bending and super-conducting wiggler fields are carefully chosen in order to provide the target emittances under the influence of intrabeam scattering but also reduce the impact of collective effects such as space-charge and coherent synchrotron radiation. Mitigation techniques for two stream instabilities have been identified and tested. The low vertical emittance is achieved by modern orbit and coupling correction techniques. Design considerations and plans for technical system, such as damping wigglers, transfer systems, vacuum, RF cavities, instrumentation and feedback are finally reviewed. | ||
| TUPPR092 | Transient Beam Losses in the LHC Injection Kickers from Micron Scale Dust Particles | 2044 |
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| Transient beam losses on a time scale of a few ms have been observed in the LHC injection kickers, occurring mainly shortly after beam injection with a strong correlation in time to the kicker pulsing. The beam losses, which have at times affected LHC availability, are attributed to micron scale ceramic dust particles detached from the alumina beam pipe and accelerated into the beam. The beam related observations are described, together with laboratory measurements of beam pipe contamination and kicker vibration, simulations of electric field in the beam pipe and the basic dynamic model. Energy deposition simulations modelling the beam losses are presented and compared to measurement. Extrapolations to future LHC operation at higher intensities and energies are made, and prospects for mitigation are discussed. | ||
| WEPPR047 | The Effect of Non-Zero Closed Orbit on Electron-Cloud Pinch Dynamics | 3033 |
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| A study on the pinch dynamics of electron cloud during a bunch passage under the effect of a single arbitrary-order multipole was presented at IPAC2011. The complexity of the pinch pattern is directly related to the order of the multipolar field. However, in a realistic situation, the proton beam will not be located in the center of the vacuum chamber. If the beam is offset a new pinch regime is encountered, where feed-down effects and asymmetry of pinch density render the dynamics more challenging. In this paper we discuss the pinch dynamics with orbit offset, including the resulting orbit variation along a bunch, and address their relevance for the incoherent effect of the electron cloud. | ||
| WEPPR075 | Monitoring the Progress of LHC Electron-Cloud Scrubbing by Benchmarking Simulations and Pressure-Rise Observations | 3105 |
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| Electron bombardment of a surface has been proven to reduce drastically the secondary electron yield of a material. This technique, known as scrubbing, is the ultimate solution to decrease the negative effects of an electron cloud build-up in any particle accelerator operating with intense beams. Its effectiveness has been already observed at the LHC. Since at the LHC no in-situ secondary-yield measurements are available, it has been necessary to develop a method to infer different key beam-pipe surface parameters by benchmarking simulations and pressure-rise observations. The method developed allows us to monitor the scrubbing process in order to decide on the most appropriate strategies for machine operation. In this paper we present the latest results of applying this method to the LHC in the fall of 2011 and early 2012, including data for the nominal bunch spacing of 25 ns. | ||
| WEPPR076 | Positron Options for the Linac-ring LHeC | 3108 |
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| The full physics program of a future Large Hadron electron Collider (LHeC) requires both pe+ and pe- collisions. For a pulsed 140-GeV or an ERL-based 60-GeV Linac-Ring LHeC this implies a challenging rate of, respectively, about 1.8·1015 or 4.4·1016 e+/s at the collision point, which is about 300 or 7000 times the past SLC rate. We consider providing this e+ rate through a combination of measures: (1) Reducing the required production rate from the e+ target through colliding e+ (and the LHC protons) several times before deceleration, by reusing the e+ over several acceleration/deceleration cycles, and by cooling them, e.g., with a compact tri-ring scheme or a conventional damping ring in the SPS tunnel. (2) Using an advanced target, e.g., W-granules, rotating wheel, sliced-rod converter, or liquid metal jet, for converting gamma rays to e+. (3) Selecting the most powerful of several proposed gamma sources, namely Compton ERL, Compton storage ring, coherent pair production in a strong laser, or high-field undulator radiation from the high-energy lepton beam. We describe the various concepts, present example parameters, estimate the electrical power required, and mention open questions. | ||
| THPPD033 | Using Permanent Magnets to Boost the Dipole Field for the High-energy LHC | 3578 |
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Funding: Work supported by the European Commission under the FP7 Research Infrastructures project EuCARD, grant agreement no. 227579. The High-Energy LHC (HE-LHC) will be a new accelerator in the LHC tunnel based on novel dipole magnets, with a field up to 20 T, which are proposed to be realized by a hybrid-coil design, comprising blocks made from Nb-Ti, Nb3Sn and HTS, respectively. Without the HTS the field would be only 15 T. In this note we propose and study the possibility of replacing the inner HTS layer by (weaker) permanent magnets that might contribute a field of 1-2 T, so that the final field would reach 16-17 T. Advantages would be the lower price of permanent magnets compared with HTS magnets and their availability. |
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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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| 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. | ||