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The Compact Linear Collider (CLIC) is a multi-TeV high-luminosity linear e+e- collider under development. For an optimal exploitation of its physics potential, CLIC is foreseen to be built and operated in a staged approach with three centre-of-mass energy stages ranging from a few hundred GeV up to 3 TeV. The first stage will focus on precision Standard Model physics, in particular Higgs and top-quark measurements. Subsequent stages will focus on measurements of rare Higgs processes, as well as searches for new physics processes and precision measurements of new states, e.g. states previously discovered at LHC or at CLIC itself. In the 2012 CLIC Conceptual Design Report, a fully optimised 3 TeV collider was presented, while the proposed lower energy stages were not studied to the same level of detail. This report presents an updated baseline staging scenario for CLIC. The scenario is the result of a comprehensive study addressing the performance, cost and power of the CLIC accelerator complex as a function of centre-of-mass energy and it targets optimal physics output based on the current physics landscape. The optimised staging scenario foresees three main centre-of-mass energy stages at 380 GeV, 1.5 TeV and 3 TeV for a full CLIC programme spanning 22 years. For the first stage, an alternative to the CLIC drive beam scheme is presented in which the main linac power is produced using X-band klystrons. The Compact Linear Collider (CLIC) is a multi-TeV high-luminosity linear e+e- collider under development. For an optimal exploitation of its physics potential, CLIC is foreseen to be built and operated in a staged approach with three centre-of-mass energy stages ranging from a few hundred GeV up to 3 TeV. The first stage will focus on precision Standard Model physics, in particular Higgs and top-quark measurements. Subsequent stages will focus on measurements of rare Higgs processes, as well as searches for new physics processes and precision measurements of new states, e.g. states previously discovered at LHC or at CLIC itself. In the 2012 CLIC Conceptual Design Report, a fully optimised 3 TeV collider was presented, while the proposed lower energy stages were not studied to the same level of detail. This report presents an updated baseline staging scenario for CLIC. The scenario is the result of a comprehensive study addressing the performance, cost and power of the CLIC accelerator complex as a function of centre-of-mass energy and it targets optimal physics output based on the current physics landscape. The optimised staging scenario foresees three main centre-of-mass energy stages at 380 GeV, 1.5 TeV and 3 TeV for a full CLIC programme spanning 22 years. For the first stage, an alternative to the CLIC drive beam scheme is presented in which the main linac power is produced using X-band klystrons.

The unprecedented requirements that new machines are setting on their diagnostic systems is leading to the development of new generation of devices with large dynamic range, sensitivity and time resolution. Beam loss detection is particularly challenging due to the large extension of new facilities that need to be covered with localized detector. Candidates to mitigate this problem consist of systems in which the sensitive part of the radiation detectors can be extended over long distance of beam lines. In this document we study the feasibility of a BLM system based on optical fiber as an active detector for an electron storage ring. The Australian Synchrotron (AS) comprises a 216m ring that stores electrons up to 3GeV. The Accelerator has recently claimed the world record ultra low transverse emittance (below pm rad) and its surroundings are rich in synchrotron radiation. Therefore, the AS provides beam conditions very similar to those expected in the CLIC/ILC damping rings. A qualitative benchmark of beam losses in a damping ring-like environment is presented here. A wide range of beam loss rates can be achieved by modifying three beam parameters strongly correlated to the beam lifetime: bunch charge (with a variation range between 1 uA and 10mA), horizontal/vertical coupling and of dynamic aperture. The controlled beam losses are observed by means of the Cherenkov light produced in a 365 μ m core Silica fiber. The output light is coupled to different type of photo sensors namely: Multi Pixel Photon Counters (MPPCs), standard PhotoMulTiplier (PMT) tubes, Avalanche PhotoDiodes (APD) and PIN diodes. A detailed comparison of the sensitivities and time resolution obtained with the different read-outs are discussed in this contribution.

The Compact Linear Collider (CLIC) is an e+/e- collider based on the two-beam acceleration principle, proposed to support precision high-energy physics experiments in the energy range 0.5-3 TeV [1]. To achieve a high luminosity of up to 6x1034cm-2s-1, the transport and preservation of a low emittance beam is mandatory. A large number and great variety of beam diagnostics instruments is foreseen to verify and guarantee the required beam quality. We discuss the status of the beam diagnostics developments and experimental results accomplished at the CLIC Test Facility (CTF) and at the Cornell University CesrTA ring accelerator.

The Test Beam Line (TBL) of the CLIC Test Facility 3 (CTF3) aims to validate the drive beam deceleration concept of CLIC, in which the RF power requested to boost particles to multi-TeV energies is obtained via deceleration of a high current and low energy drive beam (DB). Despite a TBL beam energy (150-80 MeV) significantly lower than the minimum nominal energy of the CLIC DB (250 MeV), the pulse time structure of the TBL provides the opportunity to measure beam losses with CLIC-like DB timing conditions. In this contribution, a simulation study on the detection of beam losses along the TBL for the commissioning of the recently installed beam loss monitoring system is presented. The most likely loss locations during stable beam conditions are studied by considering the beam envelope defined by the FODO lattice as well as the emittance growth due to the deceleration process. Moreover, the optimization of potential detector locations is discussed. Several factors are considered, namely: the distance to the beam, the shielding provided by the different elements of the line, the detector sensitivity and possible saturation effects of both the radiation detectors and electronics.

A Machine Development study session was held on December 6th, 2011 to test BLM quench thresholds in the IR7 dispersion suppressor (DS) for lead ion operation in the LHC at 3.5 Z TeV. High loss rates were artificially produced in the machine to allow full qualification of ion leakage with as realistic as possible loss distributions. Any potential collimation-related intensity limit imposed by a magnet quench was explored in parallel, to provide input for potential future collimation upgrade scenarios.

Protection of LHC equipment relies on a complex system of collimators to capture injected and circulating beam in case of LHC kicker magnet failures. However, for specific failures of the injection kickers, the beam can graze the injection protection collimators and induce quenches of downstream superconducting magnets. This occurred twice during 2011 operation and cannot be excluded during future operation. Tests were performed during Machine Development periods of the LHC to assess the quench margin of the quadrupole located just downstream of the last injection protection collimator in point 8. In addition to the existing Quench Protection System, a special monitoring instrumentation was installed at this magnet to detect any resistance increase below the quench limit. The correlation between the magnet and Beam Loss Monitor signals was analysed for different beam intensities and magnet currents. The results of the experiments are presented.

The Beam Loss Monitoring System (BLM) of the Large Hadron Collider (LHC) is based on parallel plate Ionization Chambers (IC) with active volume 1.5l and a nitrogen filling gas at 0.1 bar overpressure. At the largest loss locations, the ICs generate signals large enough to saturate the read-out electronics. A reduction of the active volume and filling pressure in the ICs would decrease the amount of charge collected in the electrodes, and so provide a higher saturation limit using the same electronics. This makes Little Ionization Chambers (LIC) with both reduced pressure and small active volume a good candidate for these high radiation areas. In this contribution we present measurements performed with several LIC monitors with reduced active volume and various filling pressures. These detectors were tested under various conditions with different beam setups, with standard LHC ICs used for calibration purposes

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

UFOs (Unidentified Falling Objects) are potentially a major luminosity limitation for nominal LHC operation. With large-scale increases of the BLM thresholds, their impact on LHC availability was mitigated in the second half of 2011. For higher beam energy and lower magnet quench limits, the problem is expected to be considerably worse, though. Therefore, in 2011, 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. In this paper, the state of knowledge is summarized and extrapolations for LHC operation after LS1 are presented. Mitigation strategies are proposed and related tests and measures for 2012 are specified.

The Large Hadron Collider (LHC) has been operating since 2010 at 3.5 TeV and 4.0 TeV without experiencing quenches induced by losses from circulating beams. This situation might change at 7 TeV where the quench margins in the super-conducting magnets are reduced. The critical locations are the dispersion suppressors (DSs) at either side of the cleaning and experimental insertions, where dispersive losses are maximum. It is therefore crucial to understand the quench limits with beam loss distributions alike those occurring in standard operation. In order to address this aspect, quench tests were performed by inducing large beam losses on the primary collimators of the betatron cleaning insertion, for proton and lead ion beams of 3.5 Z TeV, to probe the quench limits of the DS magnets. Losses up to 500 kW were achieved without quenches. The measurement technique and the results obtained are presented, with observations of heat loads in the cryogenics system., peer-reviewed

The history and motivation of dump threshold changes for the Beam Loss Monitoring (BLM) system throughout the 2012 run are described here. Also discussed are several dedicated beam experiments to probe the quench levels at different time scales foreseen for the end of the current run. The implications of these results to the threshold strategy are outlined. Moreover, the noise inherent to the BLM system may become an operational limitation in 2014 if running with the current dump thresholds. The most critical locations are discussed and revised thresholds are proposed that would mitigate the problem. Finally, the installation of new BLMs or the relocation of existing ones will require modifications that are explained in this document.

UFOs (“ Unidentified Falling Objects”) could be one of the major performance limitations for nominal LHC operation. Therefore, in 2011, 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 is summarized and extrapolations for LHC operation in 2012 and beyond are presented. Mitigation strategies are proposed and related tests and measures for 2012 are specified.

We report updated simulations on the interaction of macroparticles falling from the top of the vacuum chamber into the circulating LHC proton beam. The path and charge state of micron size micro-particles are computed together with the resulting beam losses, which — if high enough — can lead to the local quench of superconducting (SC) magnets. The simulated time evolution of the beam loss is compared with observations in order to constrain some macroparticle parameters. We also discuss the possibility of a “multiple crossing” by the same macroparticle, the effect of a strong dipole field, and the dependence of peak loss rate and loss duration on beam current and on beam size.

Unexpected beam loss might lead to a transition of the accelerator superconducting magnet to a normal conducting state. The LHC beam loss monitoring (BLM) system is designed to abort the beam before the energy deposited in the magnet coils reach a quench-provoking level. In order to verify the threshold settings generated by simulation, a series of beam-induced quench tests at various beam energies has been performed. The beam losses are generated by means of an orbital bump peaked in one of main quadrupole magnets (MQ). The analysis includes not only BLM data but also the quench protection system (QPS) and cryogenics data. The measurements are compared to Geant4 simulations of energy deposition inside the coils and corresponding BLM signal outside the cryostat.

One of the major known limitations for the performance of the Large Hadron Collider are so called UFOs (Unidentified Falling Objects). UFOs were first observed in July 2010 and caused numerous protection beam dumps since then. They are presumably micrometer sized dust particles that lead to fast beam losses with a duration of about 10 turns when they interact with the beam. In 2011, the diagnostics for such events are highly increased which allows estimations of the properties, dynamics and production mechanisms of the dust particles. The state of knowledge and mitigation strategies are presented.

The results of the MD performed on July the 3rd to address the quench margin at injection for Q6.L8 and Q4.L6 magnets are presented in this note.

Beam studies to address the limitations of the Phase~I collimation system were performed. The primary goal was to achieve the design loss rates of the collimation system of 500~kW, and to study the behaviour of the system and of the machine in these conditions. The beam-based determination of the quench limits of the cold magnets with highest losses, can also be addresses in this study. Beam tests consisted in increasing the loss rates at 3.5~TeV with nominal machine configuration and collimator settings in order maximise the losses in the dispersion suppressors of IR7, notably in the Q8 quadrupoles that represent the limiting location with highest leakage from IR7. The cleaning performance of IR7 is very good, with a leakage of a few 10$^{-4}$ in the Q8. Therefore, the test had to be performed with stored energies well above the safe limit.

Due to rapid progress with the LHC commissioning in 2010, set-up beam intensities were soon surpassed and damage potential was reached. One of the key systems for machine protection is the beam loss monitoring (BLM) system. Around 4000 monitors are installed at likely or critical loss locations. Each monitor has 384 associated beam abort thresholds (12 integrated loss durations from 40 μs to 84 s for 32 energy intervals). A single integrated loss over threshold on a single monitor aborts the beam. Simulations of deposited energy, critical energy deposition for damage or quench and BLM signal response backedup by control measurements determined the initial threshold settings. The commissioning and optimization of the BLM system is presented. Test procedures were used to verify the machine protection functionalities. Accidental magnet quenches were used to fine-tune threshold settings. The most significant changes to the BLM system during the 2010 run concern the injection, the collimation and the beam dump region, where hardware changes and threshold increases became necessary to accommodate for increasing beam intensity.

In particle accelerators, diverse causes may lead to the unwanted deviation of the beam particles from the nominal beam orbit and their loss in the machine. To protect from dangerous beam losses and provide valuable information on the accelerator operation, Beam Loss Monitors (BLMs) are being employed. Conventional BLMs are localised detectors, with a wide range of characteristics, depending on which the appropriate monitor for each application is selected. The optical fibre BLM is an alternative type of detector, used and examined in various facilities for its ability to cover and effectively protect long parts (of the order of 100m) of an accelerator. The Compact Linear Collider (CLIC) is a proposal for a future electron-positron collider, based on the simultaneous operation of two parallel beam lines, aiming to reach a 3 TeV center of mass energy at approximately 48km of machine length. In the present work an optical fibre based detector was developed, consisting of a quartz optical fibre coupled with a Silicon PhotonMultiplier (SiPM), to be studied as a beam loss monitor for RF accelerators, such as CLIC, and storage rings. A dedicated housing was fabricated for the photosensor and the related electronics, which optimised the system in terms of sensitivity, low noise and robustness. Instead of the most commonly used, for such detectors, Photo Multiplier Tubes (PMTs), this study made use of the SiPMs taking advantage of their insensitivity to magnetic fields and their efficiency in terms of cost and required power. The developed system was characterised for its capabilities as a BLM in the CLIC Test Facility 3 (CTF3) and in the Australian Synchrotron Light Source (ASLS). An intrinsic time resolution of 260 ps was measured, and a discrimination in beam losses with a 25cm spacing between them was demonstrated for single bunch beams. For 350 ns long electron beams, in order to distinguish simultaneous beam losses on different locations, a distance of 3m between them was required. The ability of the detector to monitor steady state losses was validated, and a method to assess all beam loss locations utilising only one initially identified, was demonstrated. The limitations introduced to BLMs from the beam loss crosstalk effect in parallel beam lines was investigated, while the sensitivity limitations induced by the RF cavity electron field emission background were estimated as not significant. The optical fibre based detector, combined with appropriate localised detectors at high risk locations, was proven a promising system for the monitoring of beam losses, for both linear accelerators and storage rings. Finally, a modified, highly sensitive version of the detector was introduced as an advanced RF cavity diagnostics tool. This was proven able of monitoring RF breakdowns and field emitted electrons along with estimating the Fowler-Nordheim field enhancement factor. Additionally, both measurements and simulations confirmed the presence of high energy electrons in the radiation environment of accelerating structures due to electron field emission.