We review the 2024 Pb-Pb ion run at the Large Hadron Collider (LHC), in terms of the operational experience, the problems encountered and the main results. This run was the second heavy-ion physics period of LHC Run 3 at 6.8 Z TeV. With only 18 days scheduled for physics data-taking, the key objective was to address the problems encountered in the 2023 Pb-Pb run and establish stable and efficient operation. Thanks to several mitigation measures, the 2023 limitations were overcome, significantly improving the machine availability. Together with substantially higher intensity, thanks to the excellent performance of the Pb ion injectors, this paved the way for a record-high performance in terms of average daily integrated luminosity with ion beams at the LHC.

In this contribution, highlights of the LHC proton and ion runs are presented, from mid-2023 to mid-2025. Starting from the LHC injector chain, the main achievements and milestones, contributing to the production of HL-LHC proton and ion beams, are covered. Thereafter, the proton luminosity production over the past years is reported, detailing luminosity levelling, optics choices, and cryogenic heat load. Concerning the Pb ion program, the commissioning of slip-stacked HL-LHC ion beams is described along with the luminosity achievements and the special 2025 light-ion run. Finally, an outlook on high-intensity tests and main activities for the upcoming long shutdown is given.

Controlled longitudinal emittance blow-up is indispensable for the operation of the Large Hadron Collider (LHC) to counteract single-bunch loss of Landau damping during the acceleration ramp. The blow-up is performed by injecting RF phase noise in a narrow frequency band into the beam phase loop, with bunch-length feedback regulating the noise amplitude. In 2024, the variation of the bunch length due to imperfect regulation caused unacceptable beam-induced heating of certain accelerator components. In this contribution, we present the results of extensive simulation scans that have been used to optimize the feedback parameters. We show how this optimization, along with a reduction of the feedback delay on the controls side, has been implemented in the LHC and significantly improved the bunch length evolution during acceleration. Finally, we discuss the results of a measurement scan performed during an operational period of five weeks to fine-tune the blow-up feedback settings.

The High Luminosity LHC (HL-LHC) project aims to increase the integrated luminosity of CERN’s Large Hadron Collider (LHC) over its exploitation era up to the end of 2041 by an order of magnitude compared to the initial LHC design value. This requires doubling the bunch intensity along with several other important changes to the LHC configuration. Dedicated beam experiments in the LHC and its injectors have already demonstrated the feasibility of reaching many of the HL-LHC project design parameters, and simulations show that some parameters could be pushed to further increase the integrated luminosity or used as mitigation measures against potential shortcomings. This paper presents a review of the latest experimental results and the possible reach of the final HL-LHC parameters.

In the era of the High-Luminosity Large Hadron Collider (HL-LHC), the main RF system will be limited in voltage and power on the injection plateau due to strong beam loading. At the same time, significant start-of ramp losses, that are originating from capture and flat bottom losses, are expected and can severely impact machine availability or even prevent the beam from reaching the collision energy. In this contribution, we present the recent experience with high-intensity beams during operation and dedicated measurements to give an update on the estimated RF voltage reach for HL-LHC beam parameters. Projections for beam losses at capture, along the flat bottom, and at the start of the ramp are calculated, taking into account also the effect of intra-beam scattering. We discuss in detail the mitigation measures put in place, such as high-efficiency klystrons, the revision of beam loss monitor thresholds at the start of the ramp, and automatic working point optimization.

The Beam Loss Monitoring System (BLM) of the Large Hadron Collider (LHC) protects the accelerator against energy deposition from beam losses. One of the most critical moments regarding beam losses is the start of the beam acceleration. During this process, particles outside the bucket will not be captured in the first seconds of the start of ramp thus being lost at the machine aperture. This is expected to be the moment of minimum beam lifetime in the LHC cycle. During Run 3, losses from these off-momentum particles triggered some beam dumps. Several studies are on-going to assess a possible limitation from this loss scenario. This contribution quantifies the beam power lost at that moment and how the losses are distributed along the accelerator by the use of a dedicated BLM loss pattern recognition algorithm.

At injection into the Large Hadron Collider (LHC), the radio frequency (RF) system is perturbed by beam-induced voltage resulting in strong RF power transients and the instant detuning of the cavities. The automatic tuning system, however, needs time for the mechanical compensation of the resonance frequency to take place. Acting back on the beam, the transients in RF power are expected to limit the maximum injected intensity by generating unacceptable beam loss. Reducing them is therefore essential to reach the target intensity during the High Luminosity (HL) LHC era. At LHC flat bottom, the cavities are operated using the half-detuning beam-loading compensation scheme. As implemented today, the tuner control algorithm starts acting only after the injection of the first longer bunch train which causes the bunches for this injection to experience the largest power spikes. This contribution presents an adapted detuning scheme for the RF cavities before injection. It was proposed as a path to decrease the transients, hence increasing the available intensity margin for the available RF power. The expected gain is evaluated in particle tracking simulations and measurements acquired during operation.

The Large Hadron Collider (LHC) Long Shutdown 2 (2019-2021), following LHC Run 2, was primarily dedicated to the upgrade of the LHC Injectors but it included also a significant amount of activities aimed at consolidation of the LHC machine components, removal of known limitations and initial upgrades in view of the High -Luminosity LHC (HL-LHC) to favour the intensity ramp -up during Run 3 (2022-2025). An overview of the major modifications to the accelerator and its systems is followed by a summary of the results of the superconducting magnet training campaign to increase the LHC operation energy beyond the maximum value of 6.5 TeV reached during Run 2. The LHC configuration and the scenarios for proton and ion operation for Run 3 are presented considering the expected performance of the upgraded LHC Injectors and the proton beam intensity limitations resulting from the heat load on the cryogenic system due to beam -induced electron cloud and impedance.

The beam longitudinal dynamics code BLonD has been developed at CERN since 2014 and has become a central tool for longitudinal beam dynamics simulations. In this paper, we present this modular simulation suite and the various physics models that can be included and combined by the user. We detail the reference frame, the equations of motion, the BLonD-specific options for radio-frequency parameters such as phase noise, fixed-field acceleration, and feedback models for the CERN accelerators, as well as the modeling of collective effects and synchrotron radiation. We also present various methods of generating multi-bunch distributions matched to a given impedance model. BLonD is furthermore a well-tested and optimized simulation suite, which is demonstrated through examples, too.

A new scenario for the first operational run of the High Luminoisty LHC (HL–LHC) era (Run 4) has recently been developed to accommodate a period of performance ramp-up to achieve an annual integrated luminosity close to the nominal HL–LHC design target. The operational scenario in terms of beam parameters and machine settings, as well as the different phases to reach optimal performance, are described here along with the impact of potential delays to key hardware components.

Finding the optimal rf injection voltage in the LHC is a trade-off between minimising capture and flat-bottom losses, which call for an increased voltage, and minimising rf power consumption as well as improving beam stability, both of which call for a reduced voltage. From the beam stability point of view, earlier particle-tracking simulations showed that the decrease of the injection voltage from 6 MV to 4 MV is beneficial. This reduction was performed in the LHC Run 2 over a three-week period in steps of 0.5 MV. The impact of different voltages and injection energy errors on the evolution of beam parameters such as bunch length and beam losses are analysed in this paper. Operation at 4 MV, maintained in the machine after the reduction period, is studied in more detail. The implications for the future High-Luminosity LHC operation with high-intensity beams are also discussed.

International high-energy particle physics research centers, like CERN and Fermilab, require excessive studies and simulations to plan for the upcoming upgrades of the world's largest particle accelerators, and the design of future machines given the technological challenges and tight budgetary constraints. The Beam Longitudinal Dynamics (BLonD) simulator suite incorporates the most detailed and complex physics phenomena in the field of longitudinal beam dynamics, required for providing extremely accurate predictions. Modern challenges in beam dynamics dictate for longer, larger and numerous simulation studies to draw meaningful conclusions that will drive the baseline choices for the daily operation of current machines and the design choices of future projects. These studies are extremely time consuming, and would be impractical to perform without a High-Performance Computing oriented simulator framework. In this article, at first, we design and evaluate a highly-optimized distributed version of BLonD. We combine approximate computing techniques, and leverage a dynamic load-balancing scheme to relax synchronization and improve scalability. In addition, we employ GPUs to accelerate the distributed implementation. We evaluate the highly optimized distributed beam longitudinal dynamics simulator in a supercomputing system and demonstrate speedups of more than two orders of magnitude when run on 32 GPU platforms, w.r.t. the previous state-of-art. By driving a wide range of new studies, the proposed high performance beam longitudinal dynamics simulator forms an invaluable tool for accelerator physicists.

A Ferro-Electric fast Reactive Tuner (FE-FRT) is a novel type of RF cavity tuner containing a low loss ferroelectric material. FE-FRTs have no moving parts and allow cavity frequencies to be changed extremely quickly (on the timescale of 100 s of ns or less). They are of particular interest for SRF cavities as they can be placed outside the liquid helium environment and without an FE-FRT it’s typically very difficult to tune SRF cavities quickly. FE-FRTs can be used for a wide variety of use cases including microphonics suppression, RF switching, and transient beam loading compensation. This promises entirely new operational capabilities, increased performance and cost savings for a variety of existing and proposed accelerators. An overview of the theory and potential applications will be discussed in detail.

While reducing the injection voltage mitigates possible rf power limitations in the HL-LHC era, it also yields larger losses. Estimation of average and bunch-by-bunch injection losses from LHC Run 2 is presented. Macroparticles simulations with CERN’s BLonD tracking code were conducted to reproduce the SPS-to-LHC capture and LHC flat-bottom losses. First estimates for HL-LHC losses as function of injection voltage and energy errors are also included. 12th International Particle Accelerator Conference (IPAC’21) Campinas, SP, Brazil, May 24—28th, 2021 L. Medina,† T. Argyropoulos, R. Calaga, H. Timko, CERN, CH-1211 Geneva, Switzerland Acknowledgments: H. Damerau, W. Höfle, N. Mounet, M. Palm, B. Salvachua, E. Shaposhnikova, K. Turaj, and J. Wenninger (CERN). References: [1] O. S. Brüning et al., doi:10.5170/CERN-2004-003-V-1, [2] The High Luminosity LHC Project, https://hilumilhc.web.cern.ch, [3] H. Timko et al., CERN-ACC-NOTE-2019-0005, [4] L. Medina et al., https://cds.cern.ch/record/2683350, [5] D. Boussard, doi:10.1109/PAC.1991.164995, [6] H. Timko et al., doi:10.18429/JACoW-HB2018TUP1WA03, [7] H. Timko et al., http://cds.cern.ch/record/2750299, [8] L. Medina et al., to be submitted, [9] H. Timko, https://indico.cern.ch/event/806637, [10] T. Argyropoulos et al., https://indico.cern.ch/event/977192, [11] CERN BLonD Simulation Suite, http://blond.web.cern.ch, [12] H. Timko et al., to be submitted, [13] H. Damerau et al., https://accelconf.web.cern.ch/IPAC2013/papers/wepea044.pdf, [14] G. Papotti, https://accelconf.web.cern.ch/e08/papers/thpc144.pdf, [15] D. Belohrad et al., https://epaper.kek.jp/d09/papers/mopd43.pdf, [16] G. Dôme, https://cds.cern.ch/record/319440, [17] D. Boussard et al., doi:10.1109/TNS.1985.4333745, [18] P. Baudrenghien et al., https://cds.cern.ch/record/485863, [19] L. Medina et al., THPAB200, this conference, [20] I. Karpov et al., doi:10.1103/PhysRevAccelBeams.24.011002, [21] N. Mounet et al., https://indico.cern.ch/event/915032, [22] I. Karpov et al., doi::10.23732/CYRCP2020-009.312 * Research supported by the HL-LHC project. † lmedinam@cern.ch

Optics measurements in storage rings employ turn-byturn data of transversely excited beams. Traditionally, to measure chromatic properties, the relative momentum is changed step-wise, which is time-consuming and almost impractical during the energy ramp. We present an optics measurement method based on adiabatic simultaneous 3dimensional beam excitation, which is more time-efficient and well fitted for the energy ramp. This method was successfully demonstrated in the LHC utilising AC-dipoles in combination either with a slow RF-frequency modulation or a driven RF-phase modulation close to the synchrotron frequency. Faster longitudinal oscillations improve the accuracy of optics parameters inferred from the synchro-betatron sidebands. This paper reports on the experimental demonstration of optics measurements based on 3D driven beam excitations and the plans for LHC Run 3.

To accurately simulate injection losses in the LHC and the High-Luminosity LHC era, a realistic beam distribution model at SPS extraction is needed. To achieve this, the beam-loading compensation by the SPS cavity controller has to be included, as it modulates the bunch positions with respect to the rf buckets. This dynamic cavity control model also allows generating a more realistic beam halo, from which the LHC injection losses will mainly originate. In this paper, the implementation of the present SPS cavity controller in CERN’s Beam Longitudinal Dynamics particle tracking code is described. Just like in the machine, the feedback and feedforward controls are included in the simulation model, as well as the generator-beam-cavity interaction. Benchmarking against measurements of the generated beam distributions at SPS extraction are presented.

Excessive studies and simulations are required to plan for the upcoming upgrades of the world's largest particle accelerators, and the design of future machines, given the technological challenges and tight budgetary constraints. The Beam Longitudinal Dynamics (BLonD) simulator suite incorporates the most detailed and complex physics phenomena in the field of longitudinal beam dynamics, required for providing extremely accurate predictions. These predictions are invaluable to the operation of existing accelerators, upcoming upgrades, and future studies. To undertake this agenda, and enable for the first time scale-out beam longitudinal dynamics simulations, we implement Hybrid-BLond, a distributed version of BLonD, that efficiently combines horizontal and vertical scaling. We propose a series of techniques that minimize the inter-node communication overhead and improve scalability. Firstly, we exploit mixed data and task parallelism opportunities. Secondly, we discuss two traffic optimisation techniques motivated by the properties of the simulated physics phenomena. Finally, we build a dynamic load-balancing scheme that coordinates effectively all the above features. We evaluate experimentally Hybrid-BLonD in an HPC cluster built with cutting-edge Intel servers and Infiniband interconnection network. Our fully-optimised implementation demonstrates an average 25.7X speedup over the previous state-of-the-art simulator when run on 32 computing nodes, across three real-world testcases.

To counteract the significant synchrotron radiation damping in the FCC-hh, a continuous longitudinal emittance blow-up is foreseen at top energy. In this paper, we study the compensation of synchrotron radiation emittance damping via RF phase noise injection. Adapting the noise bandwidth to the targeted bunch length, a good regulation of the bunch length can be achieved in the long run, while on short timescales the fluctuations remain relatively large. The steady-state bunch profile is shown and characterised with a binomial distribution. Finally, possible future developments are being discussed.