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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

In this report we assess the feasibility for installation of the $Nb_{3}$Sn MBH S2 magnet in the LHC and conclude on possible performance limitations.

The Beam Interlock System (BIS) is the backbone of CERN’s machine protection system. The BIS is responsible for relaying the so-called Beam Permit signal, initiating in case of need the controlled removal of the beam by the LHC Beam Dumping System. The Beam Permit is encoded as a specific frequency traveling over a more than 30 km long network of optical fibers all around the LHC ring. The progressive degradation of the optical fibers and the aging of electronics affect the decoding of the Beam Permit, thus potentially resulting in an undesired beam dump event and by this reduce the machine availability. Commercial off-the-shelf SFP transceivers were studied with the aim to improve the performance of the optical transmission of the Beam Permit Network. This paper describes the tests carried out in the LHC accelerator to evaluate the selected SFP transceivers and it reports the results of the test loop reaction time measurements during operation. The use of SFPs to optically transmit safety critical signals is being considered as an interesting option not only for the planned major upgrade of the BIS for the HL-LHC era but also for other protection systems., Proceedings of the 17th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2019, New York, NY, USA

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.

The powering layout of the new HL-LHC Nb₃Sn triplet circuits is the use of cryogenic bypass diodes, where the diodes are located inside an extension to the magnet cryostat, operated in superfluid helium and exposed to radiation. Therefore, the radiation hardness of different type of bypass diodes has been tested at low temperatures in CERN’s CHARM irradiation facility during the operational year 2018. The forward characteristics, the turn on voltage and the reverse blocking voltage of each diode were measured weekly at 4.2 K and 77 K, respectively, as a function of the accumulated radiation dose. The diodes were submitted to a dose close to 12 kGy and a 1 MeV equivalent neutron fluence of 2.2x10¹⁴,n/cm². After the end of the irradiation campaign the annealing behaviour of the diodes was tested by increasing the temperature slowly to 300 K. This paper describes the experimental setup, the measurement procedure and discusses the results of the measurements., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The High Luminosity LHC project (HL-LHC) will incorporate a new generation of superconducting elements such as high field superconducting magnets based on Nb₃Sn conductors and MgB₂ based high temperature superconducting links for magnet powering. In addition, the HL-LHC will also feature new generations of NbTi based magnets. The proper protection and diagnostics of those elements require the development of a new generation of integrated quench detection and data acquisition systems as well as novel methods for quench detection. The next generation of quench detection systems is to a large extent software defined and serves at the same time as high performance data acquisition system. The contribution will discuss the specific needs of HL-LHC in terms of quench detection and present recent results from tests with prototype magnets. The contribution will show the implementation of new quench detection methods such as current derivative sensors. Measures for increasing the system dependability and easing its maintenance will be explained, as well as the improved supervision architecture using Ethernet based field-bus systems for fast data transmission., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The superconducting magnets used in high energy particle accelerators such as CERN’s LHC can be impacted by the circulating beam in case of specific failure cases. This leads to interaction of the beam particles with the magnet components, like the superconducting coils, directly or via secondary particle showers. The interaction leads to energy deposition in the timescale of microseconds and induces large thermal gradients within the superconductors in the order of 100 K/mm. To investigate the effect on the superconductors, an experiment at CERN’s HiRadMat facility was designed and executed, exposing short samples of Nb-Ti and Nb₃Sn strands as well as YBCO tape in a cryogenic environment to microsecond 440 GeV/p proton beams. The irradiated samples were extracted and are being analyzed for their superconducting properties, such as the critical transport current. This paper describes the experimental setup as well as the first results of the visual inspection of the samples., Proceedings of the 10th International Particle Accelerator Conference, ISBN:978-3-95450-208-0

This paper will present the results and latest status of an extensive effort to analyse and improve the reliability and availability of the LHC. After the introduction of basic concepts and definitions, the paper reviews the performance of the LHC in 2015-2017. A direct comparison of the luminosity production years 2016 and 2017 is presented, with a focus on the main differences in the observed failure modes. Based on the lessons learnt in this time window, expectations for the performance during future LHC runs are discussed. In particular, the thought process for the evaluation of the possible full energy exploitation of the LHC is described, considering relevant factors such as the expected availability loss and the risk associated to magnet training., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

To further improve the performance and reliability of the quench detection system (QDS) for main quadrupole magnets in the Large Hadron Collider (LHC), there is a planned upgrade of the system during the long shutdown period of the LHC in 2019-2020. While improving the already existing functionalities of quench detection for quadrupole magnets and field-bus data acquisition, the enhanced QDS will incorporate new functionalities to strengthen and improve the system operation and maintenance. The new functionalities comprise quench heater supervision, interlock loop monitoring, power cycling possibility for the whole QDS and its data acquisition part, monitoring and synchronization of trigger signals, and monitoring of power supplies. In addition, the system will have two redundant power supply feeds. Given that the enhanced QDS units will replace the existing QDS units in the LHC tunnel, the units will be exposed to elevated levels of ionizing radiation. Therefore, it is necessary to design a radiation tolerant detection system. In this work, an overview of the design solution for such enhanced QDS is presented., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

For the high luminosity upgrade of the Large Hadron Collider (LHC), it is planned to replace the existing triplet quadrupole magnets with Nb₃Sn quadrupole magnets, which provide a comparable integrated field gradient with a significantly increased aperture. These magnets will be powered through a novel superconducting link based on MgB₂ cables. One option for the powering layout of this triplet circuit is the use of cryogenic bypass diodes, where the diodes are located inside an extension to the magnet cryostat and operated in superfluid helium. Hence, they are exposed to radiation. For this reason the radiation hardness of existing LHC type bypass diodes and more radiation tolerant prototype diodes needs to be tested up to the radiation doses expected at their planned position during their lifetime. A first irradiation test is planned in CERN's CHARM facility starting in spring 2018. Therefore, a cryo-cooler based cryostat to irradiate and test LHC type diodes in-situ has been designed and constructed. This paper will describe the properties of the sample diodes, the experimental roadmap and the setup installed in CHARM. Finally, the first measurement results will be discussed., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

Goal of the technology WG set by PBC: Exploration and evaluation of possible technological contributions of CERN to non-accelerator projects possibly hosted elsewhere: survey of suitable experimental initiatives and their connection to and potential benefit to and from CERN; description of identified initiatives and how their relation to the unique CERN expertise is facilitated.

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 quench detection system (QDS) of the LHC superconducting circuits is an essential part of the LHC machine protection and ensures the integrity of key elements of the accelerator. The large amount of hardwired and software interlock channels of the QDS requires a very high system dependability in order to reduce the risk of affecting the successful operation of the LHC. This contribution will present methods and tools for systematic fault tracking and analysis, and will discuss recent results obtained during the LHC production run in 2016. Measures for maintaining and further improving of the system performance will be explained. An overview of the further evolution of the LHC QDS also in view of the upcoming High Luminosity Upgrade of the LHC will be given., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The copper-stabilizer continuity measurement (CSCM) was devised in order to attain complete electrical qualification of all busbar joints, lyres, and the magnet bypass connections in the 13~kA circuits of the LHC. A CSCM is carried out at 20 K, i.e., just above the critical temperature, with resistive magnets. The circuit is then subject to an incremental series of controlled powering cycles, ultimately mimicking the decay from nominal current in the event of a magnet quench. A type test to prove the validity of such a procedure was carried out with success in April 2013, leading to the scheduling of a CSCM on all main dipole circuits up to and including 11.1 kA, i.e., the current equivalent of 6.5 TeV operation. This paper details the procedure, with respect to the type test, as well as the results and analyses of the LHC-wide qualification campaign., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

The copper-stabilizer continuity measurement - or CSCM - was devised to obtain a direct and complete qualification of the continuity in the 13 kA bypass circuits of the LHC, especially in the copper-stabilizer of the busbar joints and the bolted connections in the diode-leads. The circuit under test is brought to ~20 K, a voltage is applied to open the diodes, and the low-inductance circuit is powered with a pre-defined series of current profiles. The profiles are designed to successively increase the thermal load on the busbar joints up to a level that corresponds to worst-case operating conditions at nominal energy. In this way, the circuit is tested for thermal runaways in the joints - the very process that could prove catastrophic if it occurred under nominal conditions with the full circuit energy. Surveillance software and a numerical model were devised to carry out the analysis and ensure complete protection of the circuit from over-heating. A type test of the CSCM was successfully carried out in April 2013 on one main dipole and one main quadrupole circuit of the LHC. This paper describes the analysis procedure, the numerical model, and results of this first type test., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

Sulc, M. "Progress of the Laser-based Experiment OSQAR" in Proceedings, 9th Patras Workshop on Axions, WIMPs and WISPs (AXION-WIMP 2013) / Oberlack, Uwe, Sissol, Pierre (eds.), 2013 ; AXION-WIMP 2013 : 9th Patras Workshop on Axions, WIMPs and WISPs , 2013-06-23 - 2013-06-28, Mainz 9th Patras Workshop on Axions, WIMPs and WISPs, AXION-WIMP 2013, Mainz, Germany, 24 Jun 2013 - 28 Jun 2013; Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-PROC 67-70 (2013). doi:10.3204/DESY-PROC-2013-04/sulc_miroslav, OSQAR experiment at CERN is based on two laser methods for search of axions a scalar particles. The light shining through the wall experiment has been using two LHC dipole magnets with an optical barrier, argon laser, and cooled 2D CCD detector for the measuring of expected regenerated photons. The second method wants to measure the Vacuum Magnetic Birefringence. An optical setup with electro-optical modulator has been proposed, validated and subsequently improved in collaborating institutes. Cotton-Muton effect in nitrogen was measured by this method. Prototype of a one-meter long laser cavity was developed for this experiment., Published by Verlag Deutsches Elektronen-Synchrotron, Hamburg

Recent intensive theoretical and experimental studies shed light on possible new physics beyond the standard model of particle physics, which can be probed with sub-eV energy experiments. In the second run of the OSQAR photon regeneration experiment, which looks for the conversion of photon to axion (or Axion-Like Particle), two spare superconducting dipole magnets of the Large Hadron Collider (LHC) have been used. In this paper we report on first results obtained from a light beam propagating in vacuum within the 9 T field of two LHC dipole magnets. No excess of events above the background was detected and the two-photon couplings of possible new scalar and pseudo-scalar particles could be constrained. Recent intensive theoretical and experimental studies shed light on possible new physics beyond the standard model of particle physics, which can be probed with sub-eV energy experiments. In the second run of the OSQAR photon regeneration experiment, which looks for the conversion of photon to axion (or Axion-Like Particle), two spare superconducting dipole magnets of the Large Hadron Collider (LHC) have been used. In this paper we report on first results obtained from a light beam propagating in vacuum within the 9 T field of two LHC dipole magnets. No excess of events above the background was detected and the two-photon couplings of possible new scalar and pseudo-scalar particles could be constrained.

Two events, occurring in 2008 during commissioning of the LHC circuits, lead to fundamental changes to the scope of circuit protection. The discovery of aperture-symmetric quenches and the accidental rupture at 9kA of an interconnecting busbar resulted in an emergency program for development and implementation of new protection facilities. The new scheme comprises a distributed busbar supervision system with early warning capabilities based on high-precision splice resistance measurements and system interlocks for rapid de-excitation of the circuit in case of a sudden splice resistance increase. The developed symmetric quench detectors are digital systems with radiation-resistant FPGA logic controllers, having magnet heater firing capabilities. This program successfully allowed a safe re-powering of the collider. The concept of the new electronics boards and the powering modules will be described. More than 14¿600 extra cables and 6¿000 new detector and control cards were added to the existing QPS system. A first evaluation of the system performance as well as a number of interesting discoveries made during the commissioning will be presented., 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

Nominal beam parameters at 7TeV/c will only be reached after some years of operation, with each proton beam having a stored energy of 360MJ. However, a small fraction of this energy is sufficient to damage accelerator equipment or experiments in case of uncontrolled beam loss. The correct functioning of the machine protection systems is vital during the different operational phases already for initial operation. When operating the complex magnet system, with and without beam, safe operation relies on the protection and interlock systems for the superconducting circuits. For safe injection and transfer of beam from SPS to LHC, transfer line parameters are monitored, beam absorbers must be in the correct position and the LHC must be ready to accept beam. At the end of a fill and in case of failures beams must be properly extracted onto the dump blocks, for some failures within less than few hundred microseconds. Safe operation requires many systems: beam dumping system, beam interlocks, beam instrumentation, equipment monitoring, collimators and absorbers, etc. We describe the commissioning of the LHC machine protection system and the experience during the initial operation., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

At each interconnection between LHC main magnets, a low-resistance solder joint must be made between superconducting cables to provide a continuous current path through the superconductor, and between the surrounding copper stabilizer to provide a current path in case the cable quenches. About 10,000 such joints exist in the LHC. An extensive campaign has been undertaken to characterize and map the resistances of both types of joints. All of the superconducting cable splices were measured using the enhanced protection system of the LHC superconducting circuits. No high-resistance superconductor splices were found above 3 nano-Ohms. Non-invasive measurements of the stabilizer joints were made at 300K in 5 of the 8 sectors, and at 80K in 3 sectors. More precise local measurements were made on suspect interconnects that were opened up, and poor joints were repaired. However, it is likely that additional imperfect stabilizer joints still exist in the LHC. A statistical analysis is used to place bounds on the remaining worst-case resistances. This sets limits on the maximum operating energy of the LHC, prior to a more extensive intervention., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The series testing at 1.9 K of the 360 Short Straight Sections (SSS) for the Large Hadron Collider have started at CERN in September 2003. The SSS contain the lattice quadrupoles and correction magnets in a common cryostat. The lattice quadrupoles feature two collared coils with 56 mm bore assembled in a common yoke. The coils are wound in two-layers from 15.1 mm wide NbTi cable, insulated with polyimide tape. The paper reviews the main test results performed in superfluid helium. The magnetic field and magnetic center position of the quadrupoles and associated correctors were measured with two independent systems, namely an automated scanner and a single stretched wire technique. The quench training, the field quality and the magnetic alignment measurements are presented and discussed in terms of the specifications and expected performances of these magnets in the LHC. We discuss in detail the field quality in terms of multipole errors measured at injection and nominal field and decomposed into geometric and persistent current magnetization errors. Warm/cold correlation for the geometric multipoles and the magnetic axis is also presented., peer-reviewed

The Short Straight Section (SSS) for the Large Hadron Collider arcs, containing in a common cryostat the lattice quadrupoles and correction magnets, have now entered series production. The foremost features of the lattice quadrupole magnets are a two-in-one structure containing two 56 mm aperture, two-layers coils wound from 15.1 mm wide NbTi cables, enclosed by the stainless steel collars and ferromagnetic yoke, and inserted into the inertia tube. Systematic cryogenic tests are performed at CERN in order to qualify these magnets with respect to their cryogenic and electrical integrity, the quench performance and the field quality in all operating conditions. This paper reports the main results obtained during tests and measurements in superfluid helium. The electrical characteristics, the insulation measurements and the quench performance are compared to the specifications and expected performances for these magnets. The field in the main quadrupole is measured using three independent systems: 10-m long twin rotating coils, an automatic scanner, and single stretched wire. A particular emphasis is given to the integrated transfer function which has a spread of around 12 units rms in the production and is a critical issue. The do-decapole harmonic component, which required trimming through a change in coil shims, is also discussed. Finally, the magnetic axis measurements at room temperature and at 1.9 K, providing the nominal vertical shift for installation are reported., peer-reviewed