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To provide HL-LHC performance, the CERN LHC injector chain underwent a major upgrade during an almost 2-year-long shutdown. In the first half of 2021 the injectors were gradually re-started with the aim to reach at least pre-shutdown parameters for LHC as well as for fixed target beams. The strategy of the commissioning across the complex, a summary of the many challenges and finally the achievements will be presented. Several lessons were learned and have been integrated to define the strategy for the performance ramp-up over the coming years. Remaining limitations and prospects for LHC beam parameters at the exit of the LHC injector chain in the years to come will be discussed. Finally, the emerging need for improved operability of the CERN complex will be addressed, with a description of the first efforts to meet the availability and flexibility requirements of the HL-LHC era while at the same time maximizing fixed target physics output., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

In the framework of the LHC Injectors Upgrade project, the Beam Gas Ionisation (BGI) profile monitors installed in the Proton Synchrotron (PS) were fitted with a gas injection system capable of boosting the signal rate high enough to capture single turn acquisitions immediately after injection. This contribution reports on the studies carried out during the beam commissioning of the BGI system in a turn-by-turn matching monitor mode for its eventual implementation in an optimisation framework to preserve emittance during transfer between the PS Booster and PS. The BGI commissioning included a benchmarking with data from a wire-grid secondary emission monitor inserted into the circulating beam., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

A novel generation of fast Beam Wire Scanners (BWS), developed in the framework of the LHC Injectors Upgrade (LIU), has been recently deployed in the 3 LHC injector synchrotrons, accelerating protons from 160 MeV to 450 GeV, during the 2019-2020 LHC long shutdown. The monitors feature high precision motor controller, high resolution wire position monitoring and wide dynamic range secondary particles detectors. This contribution will document the commissioning of the 17 new systems during the accelerator complex restart in 2021, which is an exciting and challenging phase in the life cycle of an instrument. A summary of the so far achieved levels of reliability, reproducibility, detectors/DAQ bandwidth and overall accuracy, will be used to revisit the options for further improving the systems��� performance in the future., Proceedings of the 10th International Beam Instrumentation Conference, IBIC2021, Pohang, Rep. of Korea

A new generation of beam wire scanner (BWS), for transversal beam profile monitoring, is under development on the framework of the LHC Injector Upgrade project at CERN. Two pre-series prototypes have been built and installed in the Super Proton Synchrotron and Proton Synchrotron Booster, to assess the performance of the upgraded BWS concept. This contribution shows the outcome of the measurement campaigns carried out on the first BWS prototypes, both in the laboratory and with proton beams. An evaluation of a high dynamic range acquisition system for the measurement of the secondary showers produced by the beam-wire interaction is also presented., Proceedings of the 6th Int. Beam Instrumentation Conf., IBIC2017, Grand Rapids, MI, USA

The CERN Large Hadron Collider is equipped with two Beam Synchrotron Radiation (BSR) systems, one per beam, used to monitor the transverse distribution of the beam, its longitudinal distribution and the abort gap population. During the 2015-2016 winter shut-down period, one of the two BSR systems was equipped with a prototype beam halo monitor, based on the coronagraph technique, classically used in astrophysics telescopes to measure the sun corona. The system design, as well as its optics, was inherited from the coronagraph used in the KEK Photon Factory with some modifications made in order to satisfy the LHC BSR source constraints. This project is in the framework of the HL-LHC project, for which there is the requirement to monitor the beam halo at the level of 10⁻⁶ of the core intensity. This first prototype has been designed as a demonstrator system aimed at resolving a halo-core contrast in the 10-3 to 10-4 range. After discussing the design of the LHC coronagraph and its technical implementation, this contribution presents the result of the first tests with beam and the planned system upgrades for 2017., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

A new generation of fast wire scanners is being developed for the LHC Injectors Upgrade (LIU) project at CERN. These will be essential tools for transverse profile measurement with the higher brightness LIU beams, and are planned for installation in 2019 in all three synchrotrons making up the LHC injector chain. An active period of development and test has resulted in prototype installations in the SPS and PSB rings. This paper will summarise the design and report on the results to-date., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

A non-invasive laserwire system is being developed for quasi-continuous monitoring of the transverse profile and emittance of the final 160 MeV beam at CERN's LINAC4. As part of these developments, a compact laser-based profile monitor was recently tested during LINAC4 commissioning at beam energies of 50 MeV, 80 MeV and 10⁷ MeV. A laser with a tunable pulse width (1-300 ns) and ~200 W peak power in a surface hutch delivers light via a 75 m LMA transport fibre to the accelerator. Automated scanning optics deliver a free space, Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

During the long LHC shutdown 2013-2014, both the LHC and its injector chain underwent significant upgrades. The most important changes concerned increasing the maximum LHC beam energy from 4TeV to 6.5TeV and reducing the transverse emittance of the beam from the LHC injectors. These upgrades pose challenges to the measurement of the transverse beam size via Synchrotron Radiation (SR) imaging, as the radiation parameters approach the diffraction limit. Optical SR interferometry, widely used in synchrotron light facilities, was considered as an alternative method to measure the 150 'm rms beam size at top energy as it allows measurements below the diffraction limit. A system based on this technique was therefore implemented in the LHC, for the first time on a proton machine. This paper describes the design of the LHC interferometer and its two SR sources (a superconducting undulator at low energy and a bending dipole at high energy), along with the expected performance in terms of beam size measurement as compared to the imaging system. The world's first proton beam interferogram measured at the LHC will be shown and plans to make this an operational monitor will be presented., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

In the framework of the LHC Injectors Upgrade project the improvements required to achieve the parameters of the future beams for the High-Luminosity LHC are being studied and implemented. In order to deliver high brightness beams, control over the beam intensity and emittance is fundamental. Therefore, a highly accurate and reliable transverse emittance measurement is essential. Presently at the CERN Proton Synchrotron, the only operationally available emittance monitors not impacting the facility beam production are the flying wire scanners used to measure the circulating beam profile. The wire scanners will be replaced with a new generation in the next two years and a prototype is already installed. The prototype has been commissioned with beams featuring a wide range of intensities and emittances. This paper evaluates the performance of the prototype with respect to the present system via beam-based measurements. The transverse emittance measurement is discussed, considering the different potential error contributions to the measurement, such as knowledge of the machine optics and the dispersive contribution to the beam size., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

A laser-based profile monitor has been designed for commissioning of CERN's LINAC4 accelerator at 50 MeV and 100 MeV, as part of the development of a non-destructive profile and emittance monitor foreseen for the final 160 MeV beam. The system is based on a low power laser which is scanned through the H⁻ beam. Electrons, which are photo-detached from the ions by the laser, are deflected by a steerer magnet and measured by a diamond detector. The custom designed diamond detector is tailored to minimize the disturbance due to the electromagnetic field of the passing main beam. The laser source will be installed in the LINAC4 Klystron gallery located 75 m away from the profile station and an optical fiber will transport the laser to the tunnel. The laser propagation for different pulse length and peak power values was characterized with laboratory tests with such a long fiber. In this paper we describe the overall design, focusing on key elements such as the fiber-based laser transport and the electron detection with the diamond detector., Proceedings of the 4th International Beam Instrumentation Conference, IBIC2015, Melbourne, Australia

Linac4, the future 160 MeV H^{−} injector to the CERN Proton Synchrotron Booster, is presently under construction at CERN as a central step of the planned upgrade of the LHC injectors. The Linac front-end, composed of a 45 keV ion source, a Low Energy Beam Transport (LEBT), a 352.2 MHz Radio Frequency Quadrupole (RFQ) and a Medium Energy Beam Transport (MEBT) housing a beam chopper, has been installed and commissioned. Precise measurements of the longitudinalμbunch profiles of ion beams were possible with the help of a Bunch Shape Monitor (BSM) developed at INR Moscow. These were crucial for the successful commissioning of the three RF buncher cavities mounted along the MEBT and well complemented with higher precision the information provided in parallel by spectrometer measurements.

The CERN LINAC4 has been commissioned up to 12 MeV. The H^{−} beam transverse profile distributions were measured by both wire grids and wire scanners. A slit-grid system located on a temporary diagnostics bench was used to characterize the transverse emittance during the two different stages of commissioning: at the exit of the RFQ (3 MeV) and DTL1 (12 MeV). The wire signal is a balance between the negative charge deposited by the stripped electrons from the H^{−} and the charge lost due to secondary emission. Optimal settings were found for the repelling plates used to suppress secondary emission, which were confirmed by electromagnetic simulations. In addition, suppression of the secondary emission due to the beam space charge was observed. The benefit of changing the wire scanner geometry in order to minimize the cross-talk between horizontal and vertical wires and the observation of thermionic emission on carbon wires are also discussed.

As part of the CERN LHC injector chain upgrade, LINAC4 will accelerate H⁻ ions to 160 MeV, replacing the old 50 MeV proton linac. The ion source, the Low Energy Beam Transfer (LEBT) line, the 3 MeV Radio Frequency Quadrupole and the Medium Energy Beam Transfer (MEBT) line hosting a chopper, have been first commissioned in a dedicated test stand and are now tested in the LINAC4 tunnel. Diagnostics devices are installed in the LEBT and MEBT line and in a movable diagnostics test bench which is temporarily added to the MEBT exit. The paper gives an overview of all the instruments used, including beam current transformers, beam position monitors, wire scanners and wire grids for transverse profile measurements, a longitudinal bunch shape monitor and a slit-and-grid emittance meter. The movable test bench also includes a spectrometer that allows measuring the beam energy spread in conjunction with a wire grid. The present understanding of the instrumentation performance is discussed and the measurement results that allowed characterizing the 3 MeV beam in the LINAC4 tunnel are summarized., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

The new LINAC4 will accelerate H⁻ ions to 160 MeV and ultimately replace the existing 50 MeV LINAC2 in the injector chain for the LHC upgrade. During commissioning in 2013, a laserwire scanner and diamond strip detector were installed for non-invasive emittance measurements of the 3 MeV H⁻ beam. Synergy with the 3 MeV H⁻ Front End Test Stand at RAL, has stimulated collaborative development of a novel laserwire system. A low peak power (8kW) pulsed laser is fibre-coupled for remote installation and alignment free operation. Motorized focusing optics enable remote control of the thickness and position of the laserwire delivered to the vacuum chamber, in which the laser light neutralises a small fraction of H⁻ ions. Undeflected by a dipole magnet, these H atoms drift downstream, where their spatial profile is recorded by a highly sensitive diamond strip detector with ns-time resolution. We present first tests of the laserwire emittance scanner, including measurements of the photo detachment signal with respect to the background from residual gas interactions. The first laserwire transverse beam profile and emittance measurements are compared with conventional slit-grid diagnostics., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

As part of the CERN LHC injector chain upgrade, LINAC4 will accelerate H^{−} ions to 160 MeV, replacing the old 50 MeV proton linac. The ion source, the Low Energy Beam Transfer (LEBT) line, the 3 MeV Radio Frequency Quadrupole and the Medium Energy Beam Transfer (MEBT) line hosting a chopper, have been first commissioned in a dedicated test stand and are now tested in the LINAC4 tunnel. Diagnostics devices are installed in the LEBT and MEBT line and in a movable diagnostics test bench which is temporarily added to the MEBT exit. The paper gives an overview of all the instruments used, including beam current transformers, beam position monitors, wire scanners and wire grids for transverse profile measurements, a longitudinal bunch shape monitor and a slit-and-grid emittance meter. The movable test bench also includes a spectrometer that allows measuring the beam energy spread in conjunction with a wire grid. The present understanding of the instrumentation performance is discussed and the measurement results that allowed characterizing the 3 MeV beam in the LINAC4 tunnel are summarized.

Following the analysis of the results obtained during the first year of beam commissioning of the CERN multi-turn extraction, a number of changes have been introduced in the beam manipulations performed in the CERN Proton Synchrotron. This includes a different control of the linear chromaticity, the setting of the non-linear magnets used to split the beam, and the longitudinal structure in the PS. The results obtained during the 2009 run are presented and discussed in detail, including the beam performance in both the PS and the SPS, as well as the optics measurements in the transfer line between the two circular machines., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

LINAC4 is the first step in the upgrade of the injector chain for the LHC and will accelerate H⁻ ions to 160 MeV. The ion source has initially been installed in a laboratory setup where its commissioning started at the end of 2009. A slit-grid system is used to monitor the transverse emittance at the exit of the source. Measurement results have been compared to analytical and numerical predictions of the system performance, addressing the system resolution, accuracy and sensitivity. This information has been used to improve the design of a new slit-grid system required for commissioning the linac at higher energies., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

As part of the CERN LHC injector chain upgrade, LINAC4 will accelerate H⁻ ions from 45 keV to 160 MeV. A movable diagnostics test bench will be used to measure the beam parameters during the different construction stages (at 45 keV, 3 MeV and 12 MeV) at first in a laboratory setup and later in the LINAC4 tunnel. Given the beam properties at 3 and 12 MeV, the existing slit-grid system developed for the measurement of the transverse emittance at the source (45 keV) cannot be reused at these higher energies. At 3MeV and above the energy deposition would damage the steel slit in a single LINAC4 pulse. For this reason a new slit has been designed following detailed analytical and numerical simulations for different materials and geometries. The energy deposition patterns as simulated by FLUKA for the different cases are presented in detail. In addition, the choice of SEM grid wires for achieving the required measurement accuracy in terms of material, diameter and spacing, are discussed., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

A set of different beam instruments have been developed and installed on LHC to provide transverse profile monitoring. Imaging systems using intercepting screens are currently used in the transfer lines from SPS, in the dump lines and in the LHC injection regions. Betatron matching oscillations would be investigated using Optical Transition Radiation screens and fast framing cameras, installed in Point 4. Wire scanners, provide high-resolution profile measurements from injection to top beam energies, but they cannot handle the full beam intensity. Thus, for continuous beam imaging as well as abort gap monitoring, synchrotron light monitors have been developed and installed. This paper gives a brief description of the different systems and presents the first results obtained during the beam commissioning in 2009.

A detailed knowledge of the beam coupling impedance of the CERN Super Proton Synchrotron (SPS) is required in order to operate this machine with a higher intensity for the foreseen Large Hadron Collider (LHC) luminosity upgrade. A large number of Beam Position Monitors (BPMs) is currently installed in the SPS, and this is why their contribution to the SPS impedance has to be assessed. This paper focuses on electromagnetic (EM) simulations and bench measurements of the longitudinal and transverse impedance generated by the horizontal and vertical BPMs installed in the SPS machine.

The longitudinal and transverse beam coupling impedance of the first final TOTEM Roman Pot unit has been measured in the laboratory with the wire method. For the evaluation of transverse impedance the wire position has been kept constant, and the insertions of the RP were moved asymmetrically. With the original configuration of the RP, resonances with fairly high Q values were observed. In order to mitigate this problem, RF-absorbing ferrite plates were mounted in appropriate locations. As a result, all resonances were sufficiently damped to meet the stringent LHC beam coupling impedance requirements., Comment: 3 pages, 8 figures, proceedings of the 11th European Particle Accelerator Conference (EPAC08), Genova, Italy, June 2008

Experiments with two prototype long-range beam-beam compensators (current-carrying wires) during the 2004 CERN SPS run explored the efficiency of a proposed long-range beam-beam compensation for the LHC. In addition, the SPS compensators were also used to “simulate” the effect of different planes of crossing at two LHC interaction points. We present the experimental results and compare them with computer simulations.

The transverse impedance of the LHC collimators will likely dominate the overall transverse impedance in the LHC at high energies and potentially limit the maximum intensity. A prototype collimator was recently tested in the SPS. Small, but significant tune shifts depending on the collimator position have been observed using different independent high resolution tune measurement methods. In addition trapped modes predicted from numerical simulation at the ends of the collimator jaws have been identified by bench measurement techniques as well as with the beam. We present a description of the measurements and an analysis of the results.

Since June 2011 the rapid increase of the luminosity performance of the LHC has come at the expense of both increased temperature and pressure of specific, near-beam, LHC equipment. In some cases, this beam induced heating has caused delays while equipment cool-down, beam dumps and even degradation of some devices. This contribution gathers the observations of beam induced heating, attributed to longitudinal beam coupling impedance, their current level of understanding and possible actions planned to be implemented during the 1st LHC Long Shutdown (LS1) in 2013-2014.

Synchrotron radiation is currently used on LHC for beam imaging and for monitoring the proton population in the 3 microsecond abort gap. In addition to these existing detectors, a study has been initiated to provide longitudinal density profiles of the LHC beams with a high dynamic range and a 50ps time resolution. This would allow for the precise measurement both of the bunch shape and the number of particles in the bunch tail or drifting into ghost bunches. A solution is proposed based on counting synchrotron light photons with two fast avalanche photo-diodes (APD) operated in Geiger mode. One is free-running but heavily attenuated and can be used to measure the core of the bunch. The other is much more sensitive, for the measurement of the bunch tails, but must be gated off during the passage of the core of the bunch to prevent the detector from saturating. An algorithm is then applied to combine the two measurements and correct for the detector dead time, after pulsing and pile-up effects. Initial results from laboratory testing of this system are described in this paper., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Linac4 is a normal conducting 160 MeV H⁻ linear accelerator presently being installed and progressively commissioned at CERN. It will replace the ageing 50 MeV Linac2 as injector of the PS Booster (PSB), increasing at the same time its brightness by a factor of two thanks to the higher injection energy. This will be the first step of a program to increase the beam intensity in the LHC injectors for the needs of the High-Luminosity LHC project. After a series of beam measurements on a dedicated test stand the 3 MeV Linac4 front-end, including ion source, RFQ and a beam chopping line, has been recommissioned at its final position in the Linac4 tunnel. Commissioning of the following section, the Drift Tube Linac, is starting. Beam commissioning will take place in steps of increasing energy, to reach the final 160 MeV in 2015. An extended beam measurement phase including testing of stripping equipment for the PSB and a year-long test run to assess and improve Linac4 reliability will take place in 2016, prior to the connection of Linac4 to the PSB that will take place during the next long LHC shut-down., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany