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In this contribution we provide a summary of the LHC hardware commissioning campaign following the second CERN Long Shutdown (LS2), initially targeting the nominal LHC energy of 7 TeV. A summary of the test procedures and tools used for testing the LHC superconducting circuits is given, together with statistics on the successful test execution. The paper then focuses on the experience and observations during the main dipole training campaign, describing the encountered problems, the related analysis and mitigation measures, ultimately leading to the decision to reduce the energy target to 6.8 TeV. The re-commissioning of two powering sectors, following the identified problems, is discussed in detail. The paper concludes with an outlook to the future hardware commissioning campaigns, discussing the lessons learnt and possible strategies moving forward., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The energy extraction systems for the protection of the new HL-LHC superconducting magnet circuits are based on vacuum breakers. This technology allows to significantly reduce the switch opening time and increases the overall system reliability with reduced maintenance needs. This paper presents the results of detailed reliability studies performed on these new energy extraction systems. The study quantifies the risk of a failure which prevents correct protection of a magnet circuit and identifies the most critical components of the system. For this, the model considers factors such as block or component level failure probabilities, different maintenance strategies and repair procedures. The reliability simulations have been performed with AvailSim4, a novel Monte Carlo code for availability and reliability simulations. The results are compared with the system reliability requirements and provides insights into the most critical components., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

This paper highlights the outcome of the 2018 round ATS MD program, which aimed at demonstrating the feasibility of a combined ramp and telescopic squeeze as a potential key ingredient to operate the machine in Run 3, with much brighter and more energetic beams with respect to Run 2. The machine configuration which was used is first described in terms of hypercycle, optics transitions, and dedicated beam gymnastics. The various commissioning steps which were needed to obtain the green light for an intensity ramp up are described, in particular the optics measurements and corrections, the triplet aperture measurements, and the collimation-related activities. The main results are illustrated in terms of octupole threshold minimization, beam lifetime in the ramp with the machine filled with several hundred of nominal bunches or 8b4e bunch trains, and long-range beam-beam mitigation with lattice octupoles. A dedicated instability study on possible variants for the adjust beam process is also reported.

A recurrent issue of the LHC operation, observed both during Run1 and Run2 is the asymmetric behaviour of the two beams in terms of particle losses. The fact that Beam 1 shows higher losses when compared to Beam 2 is not intuitive, especially when compared to the symmetric design of the two rings. The beam-beam effects induced by the interaction of the two beams in the experimental inserts, as well as noise sources contribute to the degradation of the beam lifetime,possibly asymmetrically between the two beams. In this Machine Development study, several machine and beam configurations are considered to identify or discard some of the possible sources of this behaviour. The impact of the active filters of the main bends in the beam spectrum is tested at injection energy as a possible source of 50 Hz harmonics. A variation in the beam-beam separation induced by a crossing angle bias, and the impact of the optics choice of different phase advances between the two high-luminosity interaction points are scrutinized as source of lifetime asymmetry. Finally, the wire beam-beam compensator is tested for the first time with full beam in a suboptimal configuration and its impact is assessed.

During LHC operation, a campaign to validate the configuration of the LHC collimation system is conducted every few months. This is performed by means of loss maps, where specific beam losses are deliberately generated with the resulting loss patterns compared to expectations. The LHC collimators have to protect the machine from both betatron and off-momentum losses. In order to validate the off-momentum protection, beam losses are generated by shifting the RF frequency using a low intensity beam. This is a delicate process that, in the past, often led to the beam being dumped due to excessive losses. To avoid this, a feedback system based on the 100 Hz data stream from the LHC Beam Loss system has been implemented. When given a target RF frequency, the feedback system approaches this frequency in steps while monitoring the losses until the selected loss pattern conditions are reached, so avoiding the excessive losses that lead to a beam dump. This paper will describe the LHC off-momentum beam loss feedback system and the results achieved., Proceedings of the 17th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2019, New York, NY, USA

The HL-LHC IT string (IT string) is a test stand for the HL-LHC, whose goal is to validate the collective behaviour of the IT magnets and circuits in conditions as near as possible to the operational ones. Each individual magnet circuit will be powered through a SC link and its associated current leads up to the ultimate operational current while cooled to 1.9 K in liquid helium. The test stand will be installed in the building 2173 (SM18) and will use magnets, superconducting (SC) link, current leads, power converters and protection equipment designed for the HL-LHC with their final design, and usable for the HL-LHC. The test bench will allow a real size training for the installation and alignment, the validation of the electrical circuits, the protection scheme of the magnets, and the SC link. At this occasion, all subsystem owners will be able to fine- tune their set up and to complement or change when necessary, before they are finally installed into the HL- LHC. The powering procedures will be written and validated during the tests. These tests will also improve our knowledge of every single component and will give us the opportunity to optimize the installation and hardware commissioning procedures.

Since the beginning of the LHC commissioning, harmonics of 50 Hz have been observed in the beam spectrum. Several observations during the 2018 proton run show that these harmonics are the result of a real beam excitation, rather than an artifact of the instrumentation system. As many of these components reside in the vicinity of the betatron tune, their presence can complicate the tune measurement and tracking during operation and potentially lead to beam losses and emittance growth. This note summarizes the program of the first LHC Machine Development (MD) (Fills 7342 and 7343) dedicated to the investigation of this effect. The aim of this study is to reproduce some of the observations acquired during End-of-Fill experiments and parasitic observations, as well as to simulate the impact of dipolar noise on the beam with controlled ADT excitations.

This note summarizes the experimental results obtained during the 2018 LHC Machine Development program during the measurements campaign of the Beam-Beam Long-Range compensation using DC wires (MD3263). After the promising results obtained with the prototypes installed in IR5 in 2017, two new ones have been installed in IR1 during the EYETS 2017-18. They were commissioned with beam during the two first blocks of 2018 MDs (MD#1 and MD#2). More complex configurations were tested in the second part of the year: (i) compensation while reducing the crossing angle (MD#3) and (ii) compensation with trains in a configuration compatible with operation (MD#4).

his note summarizes the program of the LHC Machine Development to assess the potential and limits of the long-range beam-beam compensators held in 2017 (MD2202). Two compensator prototypes were installed in the machine during the EYETS16-17 and the first evidence of compensation were observed during the MD block 1 (FILLS 5898 and 5900, 9 h assigned on 1st July 2017).This study was also scheduled for the MD block 3 but could not be performed due to the machine unavailability (9 h assigned, 2 h available but unfortunately not exploitable for measurements). In MD block 4 an additional slot was scheduled (FILLS 6434 and 6435, 10 h on 29th November 2017)

During LHC operation, a campaign to validate the configuration of the LHC collimation system is conducted every few months. This is performed by means of loss maps, where specific beam losses are voluntarily generated with the resulting loss patterns compared to expectations. The LHC collimators have to protect the machine from both betatron and off-momentum losses. In order to validate the off-momentum protection, beam losses are generated by shifting the RF frequency using a low intensity beam. This is a delicate process that, in the past, often led to the beam being dumped due to excessive losses. To avoid this, a feed-back system based on the100 Hz data stream from the LHC Beam Loss system has been implemented. When given a target RF frequency, the feedback system approaches this frequency in steps while monitoring the losses until the selected loss pattern conditions are reached, so avoiding the excessive losses that lead to a beam dump. This paper will describe the LHC off-momentum beam loss feedback system and the results achieved., peer-reviewed

The compensation of the long-range beam-beam interactions using DC wires is presently under study as an option for enhancing the machine performance in the frame of the High-Luminosity LHC project (HL-LHC). The original idea dates back more than 15 years. After the installation of four wire prototypes in the LHC in 2018, a successful experimental campaign was performed during the last months. The experimental setup and the main results are reported in this paper., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The paper reports on the first high-intensity beam tests obtained with flat optics in 2018 (MD2148). This new machine configuration is described in terms of hypercycle, optics transitions, and dedicated beam gymnastics. The various commissioning steps which were needed to obtain the green light for an intensity ramp up are highlighted, in particular the optics measurements and corrections, the triplet aperture measurements, and the collimation-related activities. First collision of trains took place in the second 2018 LHC MD block. The main results are given in terms of luminosity, long-range beam-beam mitigation with lattice octupoles, and corresponding crossing angle reach.

This report discusses the feasibility and limitations for operating the LHC and HL-LHC at the ultimate beam energy of 7.5 TeV, corresponding to a main dipole magnetic field of 8.93 T and an operating current of 12748 A.

Run 2 of the CERN Large Hadron Collider (LHC) was successfully completed on 10th December 2018, achieving largely all goals set in terms of luminosity production. Following the first two-year long shutdown and the re-commissioning in 2015 at 6.5 TeV, the beam performance was increased to reach a peak luminosity of more than twice the design value and a colliding beam time ratio of 50%. This was accomplished thanks to the increased beam brightness from the injector chain, the high machine availability and the performance enhancements made in the LHC for which some methods and tools, foreseen for the High Luminosity LHC (HL-LHC) were tested and deployed operationally. This contribution provides an overview of the operational aspects, main limitations and achievements for the proton Run 2., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

This paper highlights the main results from the 2017 LHC MD program which was deployed to commission round ATS optics with high telescopic index, and ultimately to study their properties in terms of long-range beam-beam effect and octupole thresholds for coherent instabilities (MD2269). This has been the fruit of a long work all along 2017, but in the end and for the first time, a dedicated LHC MD program (4 shifts in total) opened the possibility to study a non-nominal machine configuration with unsafe beams, and then extract from this study a myriad of very conclusive results for the future operation of the LHC.

Stability diagrams quantify the LHC stability thresholds due to the beam coupling impedance. Beam Transfer Function (BTF) measurements are a direct measurements of the stability diagram and therefore of the Landau damping of proton beams. Some coherent instabilities at the LHC are still not fully understood, especially when in the presence of beam-beam long range interactions at the end of the betatron squeeze. The beam-beam excited resonances can cause diffusive mechanisms and particle distribution changes that can lead to a different stability w.r.t. expectations for a Gaussian particle distribution. To investigate limitations of the models, a BTF system has been installed in the LHC in the 2015 in order to measure the Landau damping. During past MDs several configurations have been investigated: tune shifts and tune spread of the beams have been measured as a function of the octupole currents, tunes and beam-beam long range interactions. Some measurements artifacts were observed and mitigated, however the signal quality remains too low to allow for an accurate reconstruction of the stability diagram. Improvements on the reconstruction of the stability diagram from BTF measurements will be shown in this note together with results of BTF measurements for different octupole current at injection energy.

Beam Transfer Function (BTF) measurements are direct measurement of the stability diagrams that define the stability threshold of coherent beam instabilities driven by the impedance. At the LHC, some coherent instabilities at flat top energy are still not fully understood and the BTF measurements provide a method to experimentally probe the Landau damping of the proton beams. The BTF response is sensitive to the particle distribution changes and contain information about the transverse tune spread in the beams. The BTF system has been installed in the LHC in the 2015 in order to investigate the Landau damping at different stages of the operational cycle, machine configurations (different octupole currents, crossing angles, tunes etc...) and in presence of beam-beam excited resonances that may provoke diffusion mechanisms with a consequence change of Landau damping. Past MDs showed some difficulties for the reconstruction of the stability diagram from BTF measurements and several improvements on the BTF system have been put in place in order to improve the signal to noise ratio. In this note a detailed procedure of the MD is described together with some preliminary results of BTF measurements in the presence of linear coupling.

The Large Hadron Collider (LHC) has been delivering data to the physics experiments since 2009. It first operated at a centre of mass energy of 7 TeV and 8 TeV up to the first long shutdown (LS1) in 2013-14. The 13 kA splices between the main LHC cryomagnets were consolidated during LS1. Then, it was possible to increase safely the centre of mass energy to 13 TeV. During the training campaigns, metallic debris caused short circuits in the dipole diode containers, leading to an unacceptable risk. Major interventions can only take place during multiyear shutdowns. To ensure safe operation at higher energies, hence requiring further magnets training, the electrical insulation of the 1232 dipole diodes bus-bars will be consolidated during the second LHC long shutdown (LS2) in 2019-20. The design of the reinforced electrical insulation of the dipole cold diodes and the associated project organisation are presented, including the validation tests, especially at cryogenics temperature. During LS2, maintenance interventions on the LHC cryomagnets will also be performed, following the plan based on a statistical analysis of the electrical faults. It is inscribed in the overall strategy to produce collisions at 14 TeV, the LHC design energy, and to push it further towards 15 TeV. We give a first guess on the impact on the LHC failure rate., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

During 2017, the Large Hadron Collider LHC delivered luminosity for different physics configuration in addtion to the nominal 6.5 TeV proton-proton run. About 18.5 days were dedicated to commission and to deliver special physics to the experiments. Condifurations with large beta-star of 19 m and 24 m were prepared for luminosity calibration with Van de Meer scans. A proton-proton run at 2.51 TeV took place during the last weeks of November to provide reference data for the heavy ion (Pb-Pb, p-Pb) collisions at the same equivalent nucleon energy . A very short (0.5 days) but effective ion run was scheduled where the LHC saw the first Xe beams collissions and delivered around 3 ub-1 to ATLAS and CMS. The run ended with a low event pile-up run at 6.5TeV. This contribution summarizes the operational aspects and delivered targets for the different configurations., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

In May 2017, the CERN Large Hadron Collider (LHC) restarted operations at 6.5 TeV using the Achromatic Telescopic Squeeze (ATS) scheme with a target beta-star of 40 cm in ATLAS and CMS. The number of bunches was progressively increased to a maximum of 2556 with emittances of 2.5 um. In August, several machine parameters had to be re-tuned to mitigate beam loss induced instabilities and maintain a steady increase of the instantaneous luminosity. The use of a novel beam type and filling pattern produced in the injectors, allowed filling the machine with very low emittance beam (1.5 um) achieving an equivalent luminosity with 1868 bunches. In September, the beta-star was further lowered to 30 cm (using, for the first time, the telescopic technique of the ATS) and the bunch intensity pushed to 1.25·10¹¹ protons. In the last 3 months of 2017, the LHC produced more than 500 pb-1 of integrated luminosity per day, delivering to each of the high luminosity experiments 50.6 fb-1, 10% above the 2017 target. A general overview of the operational aspects of the 2017 proton run will be presented., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

Luminosity leveling by beta* is the baseline operational scenario of HL-LHC, and this leveling technique may be used in 2018 or during run~3 depending on the beam parameters and beta* range. During this MD beta*leveling was commissioned successfully for the first time with the telescopic squeeze over the beta* range of 40 cm to 30 cm. A novel beta* leveling controls technique based on a modification of the LSA trim was also tested during the MD.

This is the first report of a three volume study on the full energy exploitation of the LHC. The report summaries the necessary preparations and consolidation work and the potential performance reach for operating the LHC at its nominal beam energy of 7TeV.

The results of an experiment aiming at probing the limitations due to strong head on beam-beam interactions are reported. It is shown that the loss rates significantly increase when moving the working point up and down the diagonal, possibly due to effects of the 10th and/or 14th order resonances. Those limitations are tighter for bunches with larger beam-beam parameters, a maximum total beam-beam tune shift just below 0.02 could be reached.

The results of an experiment aiming at colliding high brightness bunches at 6.5 TeV in the LHC and probing the interplay between external noise and head on beam-beam interaction are presented. The colliding bunches are shown to have a burn off dominated lifetime, but they experience a significant emittance growth, possibly resulting from the transverse feedback noise with non standard settings. While several features remain to be understood, the effect of noise on colliding beams seems compatible with the so-called weak-strong model.

In the 2012, 2015 and 2016 run several instabilities were developing at flat-top, during and at the end of the betatron squeeze where beam-beam interactions are present. The tune spread in the beams is therefore modified by the beam-beam long-range interactions and by other sources of spread. Studies of the stability area computed by evaluating the dispersion integral for different tune spreads couldn’t explain the observed instabilities during the squeeze and stable beams. The size of the stability area given by the computed dispersion integral depends on the transverse tune spread but its shape is defined by the particle distribution in the beams. Therefore any change of the particle distribution can lead to a deterioration of the Landau stability area. The Beam Transfer Functions (BTF) are direct measurements of the Stability Diagrams (SD). They are sensitive to particle distributions and contain information about the transverse tune spread in the beams. In this note are summarized the results of the BTF measurements acquired during the MD devoted to experimentally characterize the stability diagram for different Landau octupole currents, chromaticities, beam-beam long range separations and head-on separations.

LHC operation restarted in 2015 after the first Long Shutdown, planning for a 4-year long run until the end of 2018 (called Run 2). The beam energy was fixed at 6.5 TeV. The year 2015 was dedicated to establishing operation at the high energy and with 25 ns beams, in order to prepare production for the following three years. The year 2016 was the first one dedicated to production, and it turned out to be a record-breaking year, in which the goals in both peak and integrated luminosities with proton-proton beams were achieved and surpassed. This paper revisits 2015 and 2016, shortly highlighting the main facts in the timelines, recalling the parameters that characterized luminosity production, and sketching the main limitations and the main highlights of results for selected topics, including a particular focus on the beam physics issues., Proceedings of the North American Particle Accelerator Conf., NAPAC2016, Chicago, IL, USA

The Achromatic Telescopic Squeezing (ATS) [1] scheme offers new techniques to deliver unprecedentedly small beam spot size at the interaction points of the ATLAS and CMS experiments of the LHC, while perfectly controlling the chromatic properties of the corresponding optics (linear and non-linear chromaticities, off-momentum beta-beating, spurious dispersion induced by the crossing bumps). The first series of beam tests with ATS optics were achieved during the LHC Run I (2011/2012) for a first validation of the basics of the scheme at small intensity. In 2016, a new generation of more performing ATS optics was developed and more extensively tested in the machine, still with probe beams for optics measurement and correction at β^{*}=10 cm, but also with a few nominal bunches to establish first collisions at nominal β^{*} (40 cm) and beyond (33 cm), and to analysis the robustness of these optics in terms of collimation and machine protection. The paper will highlight the most relevant and conclusive results which were obtained during this second series of ATS tests., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The LHC collimation system provides betatron cleaning and off-momentum cleaning in two different locations of the LHC ring. In the betatron cleaning area, three primary collimators cut the primary halo in horizontal, vertical and skew planes. The beam loss monitors located downstream each of these collimators can be used to diagnose the main plane of loss. We present here a method to identify these beam losses at the LHC and decompose them as a linear combination of loss scenarios using singular value decomposition to calculate Moore-Penrose pseudoinverse of the scenario matrix. This matrix has been used to evaluate the type of beam losses in different stages of the LHC cycle., peer-reviewed

This report presents a summary of the Achromatic Telescopic Squeezing (ATS) scheme related activities which took place in 2016, where a new generation of ATS pre-squeezed and telescopic optics was successfully probed, namely: (i) down to a beta* of 10 cm with pilot bunches, and (ii) with more emphasis at intermediate beta* values of 40 cm or 33 cm where collisions were established with nominal bunches, the triplet aperture was measured and collimation measurements with pre-squeezed or moderately telescopic ATS optics were conducted.

The project consisted of two main parts. The first part was to build a FESA class which would serve as lossmap feedback controller for off-momentum lossmaps, capable of handling 100 Hz BLM data, contrary to existing controller. Thanks to the efficient management RF frequency, beam dumps during this procedure would be avoided and machine availability would improve by shortening the duration of machine validation after technical stops. The second part concerned identification of beam losses at the LHC. It was a continuation of author’s work done as Summer Student project. The aim was to identify issues with the existing losses decomposition matrix for flat top, apply necessary corrections and construct analogous matrix for injection.

HL-LHC will rely on very large beam-beam head-on shift and spread. Also LHC to push for higher luminosity will go in the same direction. A clear understanding of colling high brightness beams is fundamental to guarantee the operation of such beams and to anticipate problematics linked to such configuration. We want to explore the beam dynamics of colliding beams with high brightness: intensities as high as possible close to 2e11 ppb or higher and small emittances. The goal is to monitor the beam lifetimes and emittance behavior around the machine working point for full head-on collision and for collisions with small transverse offsets. The study aims to highlight emittance growth driven by beam-beam and possible issues with instabilities due to mode coupling at injection energy.

The interplay between head-on beam-beam interaction and external sources of noise can be a significant source of emittance growth, especially when considering large beam-beam tune shifts as for the HL-LHC upgrade project. In this experiment the emittance growth of colliding bunches with different brightness and therefore different beam-beam parameters in the presence of an external white noise source with different amplitudes is measured for different gains of the transverse feedback.

The Beam Transfer Function (BTF) measurements have been previously tested in the LHC during MD block 1 and 2. Different machine configurations (i.e. energy, beam intensity, emittance etc...) have been tested to determine a safe set-up (excitation amplitude) of the system to be completely transparent to the beam (no emittance blow-up neither losses). The aim of this experiment in MD block 3 was to characterize the Stability Diagram (SD) in the presence of diffusion mechanisms induced by excited resonances due to beam-beam long range and Landau octupole interplay. During the experiment, BTF measurements have been acquired at flat top for different settings of Landau octupole current, different chromaticity values and transverse feedback gains. In this note the description of the experiment is presented together with some preliminary results.

After a long shut-down (LS1), LHC restarted its operation on April 2015 at a record energy of 6.5TeV, achieving soon a good luminosity performance. In this paper, a luminosity model based on the three main components of the LHC luminosity degradation (intrabeam scattering, synchrotron radiation and luminosity burn-off), is compared with data from runII. Based on the observations, other sources of luminosity degradation are discussed and the model is refined. Finally, based on the experience from runI and runII, the model is used for integrated luminosity projections for the HL-LHC beam parameters., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

During the Run I in 2012, several instabilities have been observed at the Large Hadron Collider (LHC) during the Betatron squeeze. The predictions of instability thresholds are based on the computation of the beam Landau damping by calculating the Stability Diagrams (SD). These instabilities could be explained by a deterioration of the SD due to beam-beam resonance excitation which could change the particle distributions. Beam Transfer Functions (BTF) provide a measurement of the Stability Diagram. The BTFs are sensitive to the particle detuning with amplitude as well as to the particle distributions therefore they represent a powerful tool to understand experimentally the stability of beams during the LHC operational cycle. First BTF measurements at the LHC are presented for different machine configurations and settings and compared to predictions., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

In 2015 the Large Hadron Collider (LHC) entered the first year in its second long Run, after a 2-year shutdown that prepared it for high energy. The first two months of beam operation were dedicated to setting up the nominal cycle for proton-proton operation at 6.5 TeV/beam, and culminated with the first physics with 3 nominal bunches/ring at 13 TeV CoM on 3 June. The year continued with a stepwise intensity ramp up that allowed reaching 2244 bunches/ring for a peak luminosity of ~5·10³³ cm⁻²s^{−1} and a total of just above 4 fb-1 delivered to the high luminosity experiments. Beam operation was shaped by the high intensity effects, e.g. electron cloud and macroparticle-induced fast losses (UFOs), which on a few occasions caused the first beam induced quenches at high energy. This paper describes the operational experience with high intensity and high energy at the LHC, together with the issues that had to be tackled along the way., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

SMAAC LS1 - last standard insulation in the LHC

The first LHC long shutdown was driven by the need to consolidate the 13 kA splices between the superconducting magnets to safely attain its center of mass design energy of 14 TeV. Access to the splices requires the opening of welded sleeves by machining. After consolidation, the sleeves are re-welded using a TIG orbital welding. The welding process has been modified from the original “as-new” installation in order to better adapt to the “as repaired” situation. The intervention has been thoroughly prepared through qualifications, organisation of teams, their training and follow-up. Quality control is based on the qualification of equipment, process and operators; the recording of production parameters; regular process audits and production witness samples; visual inspection through an official certifying body. The paper also describes welding and quality control of special intervention cases, with issues of difficult access requiring innovative solutions. This work concerns over 10 000 welds and a team of 40 engineers and technicians over a period of 18 months. The experience and lessons learnt will be applicable to similar large complex projects., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Last overheated splice consolidation

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

After the incident on the 19th September 2008 and more than one year without beam the commissioning of the LHC started again on November 20, 2009. Progress was rapid and collisions under stable beam conditions were established at 1.2 TeV within 3 weeks. In 2010 after qualification of the new quench protection system the way to 3.5 TeV was open and collisions were delivered at this energy after a month of additional commissioning. This paper describes the experiences and issues encountered during these first periods of commissioning with beam., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

On 19th September 2008 the Large Hadron Collider (LHC) experienced a serious incident, caused by a bad electrical joint, which stopped beam operation just a few days after its beginning. During the following 14 months the damage was repaired, additional protection systems were installed and the measures to avoid a similar incident were taken (i.e. new layer of the Magnet Quench Protection System [nQPS], more efficient He release valves). As a consequence, a large number of powering tests had to be repeated or carried out for the first time. The re-commissioning of the already existing systems as well as the commissioning of the new ones has been carefully studied, then performed taking into account the history of each of the eight LHC sectors (warm-up, left at floating temperature,¿). Moreover, a campaign of measurements of the bus-bar splice resistances has been carried out with the nQPS in order to spot out non conformities, thus assessing the risk of the LHC operation for the initial energy level. This paper discusses how the guidelines for the LHC 2009 re-commissioning were defined, providing a general principle to be used for the future re-commissioning., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Following the LHC injection tests of 2008, two injection tests took place in October and November 2009 as preparation for the LHC restart on November 20, 2009. During these injection tests beam was injected through the TI2 transfer line into sector 23 of ring 1 and through TI8 into the sectors 78, 67 and 56 of ring 2. The beam time was dedicated to injection steering, optics measurements and debugging of all the systems involved. Because many potential problems were sorted out in advance, these tests contributed to the rapid progress after the restart. This paper describes the experiences and issues encountered during these tests as well as related measurement results., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan