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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

CERN accelerators underwent a period of long shutdown from the end of 2018 to 2020. During this time frame, significant hardware and software upgrades have been put in place to increase the performance of both proton and ion accelerator chains in the High Luminosity LHC era. In the context of the CERN lead ion chain, 2021 has been mainly devoted to restore the injectors’ performance and to successfully prove the slip-stacking technique in SPS. In this paper we summarise the key milestones of the ion beam commissioning and the achieved beam performance for the Linac 3 (including the source), LEIR and PS accelerators, together with an outlook on 2022 operation., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

An Electro-Optic Beam Position Monitor (EO-BPM) is being developed as a high-frequency (up to 10 GHz) diagnostic for crabbing and Head-Tail intra-bunch detection at the HL-LHC. Following an earlier prototype at the SPS that demonstrated single-pickup signals, an upgraded design of an interferometric EO-BPM has been beam-tested at the HiRadMat facility for validation and characterisation studies. In the new design, the fibre-coupled Mach-Zehnder interferometer arms are modulated by lithium niobate waveguides integrated in an upgraded opto-mechanical arrangement that has been developed to produce a highly magnified image field replica of the passing Coulomb field. A new detection technique that is directly sensitive to the interferometric optical difference signal from opposite EO buttons has been applied to measure single-shot bunches for the first time. A transverse resolution study over a ±20 mm range at 3 GHz bandwidth produced the first successful electro-optic bunch-by-bunch position measurement at the HiRadMat in-air extraction line. The results of this campaign show promise for an in-vacuum design that is in production for beam tests at the SPS during Run-3 of the LHC., Proceedings of the 11th International Beam Instrumentation Conference, IBIC2022, Kraków, Poland

The Large Hadron Collider (LHC) is protected against potentially dangerous beam losses by a distributed system based on some four thousand beam loss monitors. To provide an additional level of safety, the LHC has been equipped with a system to detect fast beam intensity drops and trigger a beam dump for potentially dangerous rates. This paper describes the architecture of the system and its signal processing, optimized to cope with dump thresholds in the order of 0.01 % of the circulating beam intensity. The performance of the installed system is presented based upon beam measurements., Proceedings of the 11th International Beam Instrumentation Conference, IBIC2022, Kraków, Poland

The betatron tune in the Large Hadron Collider (LHC) is measured using a Base-Band-Tune (BBQ) system. Processing of these BBQ signals is often perturbed by 50Hz noise harmonics present in the beam. This causes the tune measurement algorithm, currently based on peak detection, to provide incorrect tune estimates during the acceleration cycle with values that clearly oscillate between neighbouring harmonics. The LHC tune feedback cannot be used to its full extent in these conditions as it relies on stable and reliable tune estimates. In this work we present two alternative tune measurement algorithms, designed to mitigate this problem by ignoring small frequency bands around the 50Hz harmonics and estimating the tune from spectra with gaps. One is based on Gaussian Processes and the other is based on a weighted moving average. We compare the tune estimates of the new and present algorithms and put forward a proposal that can be implemented during the renovation of the BBQ system for the next physics run of the LHC., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

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

Intra-bunch transverse instabilities are routinely measured in the LHC using a "Head-Tail Monitor" based on sampling a wide-band BPM with a high-speed digitiser. However, these measurements are limited by the dynamic range and short record length possible with typical commercial oscilloscopes. This paper will present the initial results from the LHC Multi-Band Instability Monitor, a new technique developed to provide information on the beam stability with a high dynamic range using frequency domain analysis of the transverse beam spectrum., Proceedings of the 7\textsuperscript{th} Int. Beam Instrumentation Conf., IBIC2018, Shanghai, China

Crab cavities are a critical component within the High Luminosity upgrade project for the Large Hadron Collider (HL-LHC). It is foreseen to use crab cavities in order to compensate the geometric luminosity reduction factor (reduction of the luminous region at the Interaction Point [IP]) due to the beam crossing angle (required for minimizing the impact of the long range beam-beam effects on the single particle beam dynamics) and increase the number of collisions per bunch crossing. In 2018 the first beam tests of crab cavities with protons were performed in the Super Proton Synchrotron (SPS) at CERN. Two vertical superconducting cavities of the Double Quarter Wave (DQW) type were fabricated and installed in the SPS to verify some key components of the cavity design and operation. This paper will present some of the first results relating to the proton beam dynamics in the presence of crab cavities., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

Requirements for diagnostics of injection matching and beam space charge effects have driven studies at CERN using high sensitivity tune measurement systems based on diode detectors for the observation of quadrupolar beam oscillations in the frequency domain. This has led to an extension of such tune systems to include a channel optimised for quadrupolar oscillation measurements. This paper presents the principles of such measurements, the developed hardware and example measurements., Proceedings of the 8th International Beam Instrumentation Conference, IBIC2019, Malmö, Sweden

Recurrent beam dumps significantly perturbed the operation of the CERN LHC in the summer months of 2017, especially in August. These unexpected beam dumps were triggered by fast beam losses that built up in the cryogenic beam vacuum at the half-cell 16 left of LHC-IP2 and were detected either at that location but mainly in the collimation insertions. This contribution details the experimental observables (beam losses, coherent instabilities, heat load to cryogenic system, vacuum signals), the extent of the understanding of the beam loss and instability mechanisms and the mitigation steps and new settings that allowed recovering the luminosity performance of the LHC for the rest of the Run., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

A high bandwidth transverse feedback demonstrator system has been devised within the LARP framework in collaboration with SLAC for the LHC Injectors Upgrade (LIU) Project. The initial system targeted the Super Proton Synchrotron (SPS) at CERN to combat TMCI and electron cloud instabilities induced for bunches with bunch lengths at the 100 MHz scale. It features a very fast digital signal processing system running at up to 4~GS/s and high bandwidth kickers with a frequency reach of ultimately beyond 1~GHz. In recent years, the system has gradually been extended and now includes two stripline kickers for a total power of 1~kW delivering correction signals at frequencies of currently more than 700~MHz. This talk will cover recent studies using this demonstrator system to overcome TMCI limitations in the SPS. We will conclude with future plans and also briefly mention potential applications and requirements for larger machines such as the LHC or the HL-LHC., Proceedings of the 61\textsuperscript{st} ICFA ABDW on High-Intensity and High-Brightness Hadron Beams, HB2018, Daejeon, Korea

The transverse mode coupling instability (TMCI) in the SPS has been identified as one of the potential performance limitations for future high intensity LHC beams that will be required for the High Luminosity (HL)-LHC era and is being addressed by the LHC Injector Upgrade Project (LIU). A potential mitigation can be provided by wideband feedback systems with a frequency reach of about 1 GHz . For this reason, the development of a prototype system has been started in a CERN collaboration within the US-LARP framework in 2008. In this report we present latest experimental results in 2017 where this prototype system was used in single and multi-bunch studies. In particular, a successful mitigation against TMCI at injection could be demonstrated in single bunch studies., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

In 2017, the LEIR accelerator has been operated with Xe³⁹⁺ beam for fixed target experiments in the SPS North Area. The different ion species, with respect to the usually operated Pb⁵⁴⁺, allowed for additional comparative measurements of tune shift versus intensity at injection energy both in coasting and bunched beams. The fast transverse instability observed for high accumulated intensities has been as well characterized and additional observations relevant to impedance have been collected from longitudinal Schottky signal and BTF measurements. The results of these measurements are summarised and compared to the currently developed machine impedance model., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The Extra Low ENergy Antiproton ring (ELENA) at CERN entered the commissioning phase in November 2016 using H⁻ ions and antiprotons to setup the machine at the different energy plateaus. The low intensities and energy of the ELENA beam generate very weak signals making beam diagnostics very challenging. With a circulating beam current of less than 1 μA and an energy where the beam annihilates in less than a few microns of matter, special care was taken during the design phase to ensure an optimal performance of these measurement devices once installed on the ring and transfer lines. A year on we present the performance of the various devices that have been deployed to measure the beam parameters from the extraction point of the Antiproton Decelerator (AD), through the ELENA ring and in the experimental lines., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

An Electro-Optic Beam Position Monitor is being developed for the HL-LHC, aimed at the detection of high order proton bunch instabilities and as a diagnostic for crabbed bunch rotation. A prototype EO-BPM was installed in the CERN SPS during 2016 and recent first beam tests of the EO pick-up are presented. The tested system comprises two opposing pick-ups, each equipped with 5mm cubic LiNbO3 crystals in vacuum, illuminated by polarized light from a fibre-coupled CW 780 nm laser. The 1 ns proton bunch induces a temporal modulation in the polarization state of light emerging from each birefringent crystal, by the Pockels effect. The modulation is analyzed, then recorded by a fibre-coupled fast photodetector in the counting room. The very first experimental signals obtained by the EO-pickups of a passing proton bunch are reported as a proof of concept of the idea. Moreover, the expected response of the beam signal is measured with respect to remotely controlled changes in the polarizer and analyzer orientations. The data are compared with analytical and electromagnetic simulations. Following the first detection, we report the latest status of the prototype design and future prospects., Proceedings of the 6th Int. Beam Instrumentation Conf., IBIC2017, Grand Rapids, MI, USA

The operation during the summer months of the 2017 Run of the CERN LHC was plagued with fast beam losses that repeatedly occurred in the 16th arc half-cell at the left of IP2 as well as in the collimation insertion, leading to unwanted beam dumps. Transverse coherent oscillations were observed during this fast process. We detail here the experimental observations of coherent motion that al-lowed shedding light upon parts of the mechanism and identify the potential mitigations that were successfully implemented in the second half of the Run., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The LHC Schottky monitors have the potential to measure and monitor some important beam parameters, tune, momentum spread, chromaticity and emittance, in a non-invasive way. We present recent upgrade and improvement efforts of the transverse LHC Schottky systems operating at 4.8 GHz. This includes optimization of the slotted waveguide pickups and a re-design of the RF front-end electronics to detect the weak, incoherent Schottky signals in presence of large, coherent beam harmonics., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

A limiting factor on the maximum beam intensity that can be stored in the Large Hadron Collider (LHC) is the growth of transverse beam instabilities. Understanding and mitigating these effects requires a good knowledge of the beam parameters during the instability in order to identify the cause and provide the necessary corrections. This paper presents the suite of beam diagnostics that have been put into operation to monitor these beam instabilities and the development of a trigger system to allow measurements to be made synchronously with multiple instruments as soon as any instability is detected., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

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

The radiofrequency and transverse damper feedback systems of the Large Hadron Collider digitize beam phase and position measurements at the bunch repetition rate of 40 MHz. Embedded memory buffers allow a few milliseconds of full rate bunch-by-bunch data to be retrieved over the VME bus for diagnostic purposes, but experience during LHC Run I has shown that for beam studies much longer data records are desirable. A new "observation box" diagnostic system is being developed which parasitically captures data streamed directly out of the feedback hardware into a Linux server through an optical fiber link, and permits processing and buffering of full rate data for around one minute. The system will be connected to an LHC-wide trigger network for detection of beam instabilities, which allows efficient capture of signals from the onset of beam instability events. The data will be made available for analysis by client applications through interfaces which are exposed as standard equipment devices within CERN's controls framework. It is also foreseen to perform online Fourier analysis of transverse position data inside the observation box using GPUs with the aim of extracting betatron tune signals., Proceedings of the 15th Int. Conf. on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2015, Melbourne, Australia

This paper will present the new modular architecture adopted as a baseline by the CERN Beam Instrumentation Group for its future acquisition system developments. The main blocks of this architecture are: radiation tolerant digital front-ends; a latency deterministic multi gigabit optical link; a high pin count FMC carrier used as a VME-based back-end for data concentration and processing. Details will be given on the design criteria for each of these modules as well as examples of their use in systems currently being developed at CERN., Proceedings of the 15th Int. Conf. on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2015, Melbourne, Australia

This report presents the work completed while the author was working for the BE-RF-FB group at the European Organization for Nuclear Research during the period of June to December 2010. The placement was completed as part of the University of Glasgow course ‘Industrial Project EE5’ which is requirement during the final year of the Degree of Master of Engineering. The report will pay particular attention to the hardware and firmware design of the ‘Dual Trigger Unit’, a new electronic module for the low-level RF system of the Super Proton Synchrotron accelerator which generates delayed timing pulses in order to trigger other hardware. In addition to this, the report will cover other projects completed during the period, including work on a prototype of the ‘VME Peak Detector’ card for the Large Hadron Collider beam observation system.

Throughout 2015, many measurements of the minimum stabilizing octupole current required to prevent coherent transverse instabilities have been performed. These measurements allow the LHC impedance model at flat top to be verified and give good indicators of future performance and limitations. The results are summarized here, and compared to predictions from the simulation code DELPHI., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

A novel electro-optic beam position monitor capable of rapidly (, Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

At the HL-LHC, proton bunches will be rotated by crab-cavities close to the interaction regions to maximize the luminosity. A method to rapidly monitor the transverse position of particles within each 1ns bunch is required. A novel, compact beam diagnostic to measure the bunch rotation is under development, based on electro-optic crystals, which have sufficient time resolution (, Proceedings of the 4th International Beam Instrumentation Conference, IBIC2015, Melbourne, Australia