Since 2010 the Large Hadron Collider (LHC) is the accelerator with the highest stored energy per ... more Since 2010 the Large Hadron Collider (LHC) is the accelerator with the highest stored energy per beam, with a record of 140 MJ at a beam energy of 4 TeV, almost a factor of 50 higher than other accelerators. With such a high stored energy, machine protection aspects set the boundary conditions for operation during all phases of the machine cycle. Only the low-intensity commissioning beams can be considered as relatively safe. This document discusses the interplay of machine operation and machine protection at the LHC, from commissioning to regular operation.
Current frontier accelerators explore regimes of increasing power and stored energy, with beam en... more Current frontier accelerators explore regimes of increasing power and stored energy, with beam energies spanning more than three orders of magnitude from the GeV to the TeV scale. In many cases the high beam power has to cohabit with superconducting equipment in the form of magnets or RF cavities requiring careful control of losses and of halos to mitigate quenches. Despite their large diversity in physics goals and operation modes, all facilities depend on their Machine Protection Systems (MPS) for safe and efficient running. This presentation will aim to give an overview of current MPS and on how the MPS act on or control the beams. Lessons from the LHC and other accelerators show that ever tighter monitoring of accelerator equipment and of beam parameters is required in the future. Such new monitoring systems must not only be very accurate but also be extremely reliable to minimize false alarms. Novel MPS ideas and concepts for linear colliders, high intensity hadron accelerators...
The HL-LHC project requires major underground civil engineering, with the excavation of large und... more The HL-LHC project requires major underground civil engineering, with the excavation of large underground structures in order to host new equipment. The tunnels construction and other civil engineering works will therefore take place in parallel with the LHC operation. The effect of vibrations induced by civil engineering activities needs to be evaluated in order to take required corrective actions. For this purpose, experiments and measurements have been performed in order to characterize the vibration sources and to determine the vibration transfer path through the rock, the tunnel floor and the accelerator component structures. The transfer functions’ amplitude and phase were determined with dedicated tools for molasses rock for both horizontal and vertical vibrations. An experimental modal analysis was carried on a LHC final focusing magnet. The campaign of measurements has been performed to confirm the effect of the vibrations created on the surface on the circulating beam orbi...
In 2015 the Large Hadron Collider (LHC) restarted for Run 2 after a two year long shutdown to con... more In 2015 the Large Hadron Collider (LHC) restarted for Run 2 after a two year long shutdown to consolidate the machine for operation at nominal beam energy. Following a few months of recommissioning and magnet training, the LHC operated for the first time at an energy of 6.5 TeV. The aim of this first year was to master operation at the higher energy and with beams of 25 ns spacing. In 2016 the performance could be pushed based on the experience of 2015, culminating with a luminosity 40% above the design value of 10 34 cm -2 s -1 . With an availability for luminosity production of 50% integrated luminosities of 40 fb -1 were delivered to each of the two large experiments. The status of the machine operation, performance and prospects for the rest of Run 2 and Run 3 will be discussed.
The next generation hadron accelerators will operate with MW beams or store beams with an energy ... more The next generation hadron accelerators will operate with MW beams or store beams with an energy of many 100 MJ. Such accelerators must be protected by fast and very reliable interlock systems to avoid damage due to uncontrolled beam loss. Machine protection will constrain operation, but some operational flexibility is still required for commissioning and performance optimization. This is a substantial challenge for control systems and application programs. New tools are developed to face those challenges: critical settings management, software interlocks, role based access to equipment, automatic accelerator mode recognition etc. This talk presents some of the challenges and tools. Experience with novel approaches are discussed.
During the two week SPS operation period for CNGS in October 2007 approximately 47'000 extraction... more During the two week SPS operation period for CNGS in October 2007 approximately 47'000 extractions were recorded with an average intensity on target of 1.7 × 10 13 protons per extraction. Although this period was rather short it presented an excellent opportunity to study the stability and performance of the primary CNGS beam from extraction to target. This document presents results on beam position stability and beam losses for the CNGS running period. The beam stability on target over the 15 day period was found to be excellent and well within the tolerance for target protection. Beam losses on the extraction septa could be maintained at a low level for the entire period. The analysis of the interlock system data revealed no malfunctioning of the interlock system. It revealed however that in stable periods 3% of the extractions were not triggered and that false interlocks were the cause of most of the missing extractions.
The Multi-Turn Extraction (MTE), a new type of extraction based on beam trapping inside stable is... more The Multi-Turn Extraction (MTE), a new type of extraction based on beam trapping inside stable islands in horizontal phase space, has been commissioned during the 2008 run of the CERN Proton Synchrotron. Both singleand multi-bunch beams with a total ...
The synchrotron tunes depend on energy loss and total accelerating voltage. This dependency can b... more The synchrotron tunes depend on energy loss and total accelerating voltage. This dependency can be used to extract the beam energy in a very precise way. Since the energy calibration of LEP 2 requires the highest possible accuracies detailed systematic studies of the parameters involved in the analysis are necessary. This paper presents method, systematic studies and results of the energy determination from the synchrotron.
Aperture measurements in the ALICE interaction region were carried out to determine a safe config... more Aperture measurements in the ALICE interaction region were carried out to determine a safe configuration of β * and crossing angle for the 2011 heavy ion run. Proton beams were used at the end of the proton run, after the commissioning of the squeeze to β * = 1 m in IR2. In this paper, the results of aperture measurements are summarised and the final collision configuration is presented. Results of parasitic measurements of the effect of non-linear triplet fields with large orbit bumps in the IRs are also summarised.
PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268)
The Large Electron-Positron Collider (LEP) at CERN closed down in November 2000. During the year ... more The Large Electron-Positron Collider (LEP) at CERN closed down in November 2000. During the year 2000 electron-positron collisions were established at centre-ofmass energies of up to 209 GeV. The energy reach of LEP was thus extended by another 7 GeV compared to the year 1999. At the same time the luminosity production was kept high and the total delivered luminosity for the year was 233 pb -1 . High beam energy and high luminosity extended the discovery reach of LEP. The successful energy increase of LEP is analysed and the operation and performance in the regime of ultra-strong damping is described.
First proton-nucleus collisions in the LHC: the p-Pb pilot physics
During the night of 12-13 September 2012 the LHC collided protons with lead nuclei for the first ... more During the night of 12-13 September 2012 the LHC collided protons with lead nuclei for the first time, demonstrating the feasibility of hybrid collisions despite the basic two-in-one magnet design. The centre-of-mass energy was 5 TeV per colliding nucleon pair, "Stable Beams" were declared 9 hours after the first injection of Pb beams in 2012. The integrated luminosity delivered to the four large LHC experiments was sufficient to yield new physics results. Within the same fill, stable beams were declared twice more, with the collision points displaced longitudinally by ±0.5 m from their usual locations. We provide a general overview of this p-Pb pilot physics fill before focusing on beam data at injection energy and at flat-top, before stable beams for physics were declared. We monitored the beam parameters throughout the fill and present an analysis of their evolution based on a simulation of intra-beam scattering (IBS), synchrotron radiation and the consumption of the beam intensity by collisions ("luminosity burn-off"). We also present some considerations on beam-beam effects with unequal beam sizes and the pilot run is compared, in this respect, to expectations for the forthcoming physics run in January. This pilot run was a major step in the preparation of the physics run. However it was not possible to perform an additional feasibility test designed to clarify the limits to the intensity of two beams injected and ramped with unequal revolution frequencies. We describe the plan for this test and discuss the reasons why it could not be carried out
Injection losses are compared for 2010 and 2011 operation. Mitigation techniques which were put i... more Injection losses are compared for 2010 and 2011 operation. Mitigation techniques which were put in place in 2010 to reduce losses at injection are described. Issues in 2011 operation, their potential improvements and the performance reach for 2012 are shown.
We have measured the properties of Z°-,bl] decays using a sample of 944 inclusive muon events, co... more We have measured the properties of Z°-,bl] decays using a sample of 944 inclusive muon events, corresponding to 18000 hadron events obtained with the L3 detector at LEP. We measured the partial decay width of the Z ° into bb, Fb6 = 353 _+ 48 MeV, and we determined the vector coupling of the Z ° to the b quark; g~,(b)=0.095 _+ 0.047. We measured the forward-backward charge asymmetry in e + e-~bl~ events at ,,/s ~ Mz, and obtained Ab~ = 13.3 _+ 9.9%.
At the Large Hadron Collider (LHC) with nominal parameters at 7 TeV, each proton beam has an ener... more At the Large Hadron Collider (LHC) with nominal parameters at 7 TeV, each proton beam has an energy of more than 330 MJ threatening to damage accelerator equipment in case of uncontrolled beam loss. To prevent such damage, kickers are fired in case of failure deflecting the beams into dump blocks. The dump blocks are the only elements that can safely absorb the beams without damage. The time constant for particle losses depends on the specific failure and ranges from microseconds to several seconds. Starting with some typical failure scenarios, the strategy for the protection during LHC beam operation is illustrated. The systems designed to ensure safe operation, such as beam dump, beam instruments, collimators / absorbers and interlocks are discussed.
During Run 2 the LHC operation will be based on the experience gained in Run 1. However the LHC w... more During Run 2 the LHC operation will be based on the experience gained in Run 1. However the LHC will be operated near to its design energy. Many operational configurations can be considered to improve efficiency and reduce the impact of the longer time required by each operational phase. The expected changes in the magnetic model and the impact of the data updates with the corrections calculated during LS1 are presented together with a general overview of the operational cycle, including time, challenges and possible improvements of each phase.
This poster presents an overview of beam based feedback systems at the LHC at CERN. It will cover... more This poster presents an overview of beam based feedback systems at the LHC at CERN. It will cover the system architecture which is split into two main parts – a feedback controller (OFC) and a service unit (OFSU). The paper presents some issues encountered during beam commissioning and lessons learned including follow-up from a recent review which took place at CERN Software Architecture for the LHC Beam-based Feedback System L. K. Jensen, M. Andersen, K. Fuchsberger, S. Jackson, L. Ponce, R. J. Steinhagen, J. Wenninger, CERN, Geneva, Switzerland FEEDBACK SERVER (OFC) The OFC/OFSU server combination has allowed running the LHC beam-based feedback reliably allowing rapid setting-up of new running scenarios. This has allowed subsequent feed-forward reducing the required real-time corrections to deal with slowly drifts of position and betatron tunes. During LS1, a small team has been put in place with an aim of looking critically at performance, design and implementation decisions and ...
Long-range beam-beam collisions may limit the dynamic aperture and the beam lifetime in colliders... more Long-range beam-beam collisions may limit the dynamic aperture and the beam lifetime in colliders. Their effect can be compensated by a current-carrying wire mounted parallel to the beam. A compensation scheme based on this principle has been proposed for the Large Hadron Collider (LHC). To demonstrate its viability, a prototype wire was installed at the CERN SPS in 2002. First successful machine experiments explored the dependence of beam loss, beam size, and beam lifetime on the beam-wire distance and on the wire excitation. They appear to confirm the predicted effect of the long-range collisions on the beam dynamics. In 2004, two further wires will become available, by which we can explicitly demonstrate the compensation, study pertinent tolerances, and also compare the respective merits of different beam-beam crossing schemes for several interaction points.
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Papers by Jorg Wenninger