The electron-positron Future Circular Collider (FCC-ee) will initially operate at the Z-pole energy of 45.6 GeV with beams composed of 12\,000 bunches, storing a total energy of 17.5 MJ per beam. Combined with small emittances, this results in extremely high beam energy densities that pose a significant damage risk to accelerator components. A comprehensive assessment of powering failure scenarios is therefore essential to ensure safe machine operation. This study evaluates the impact of a powering failure in one of the main dipole circuits using the Local Chromaticity Correction (LCC) lattice configuration. Multi-turn bunch tracking simulations are performed to determine the beam response and assess failure criticality. We interpret these novel results with respect to previously established results for the Global Hybrid Correction (GHC) lattice. Horizontal orbit excursions are found to develop over a significantly longer timescale than for the GHC lattice. The underlying physics of this behaviour is analysed in detail, with emphasis on the role of the modified sextupole configuration in the arcs. Based on these findings, the implications for machine protection system design, including interlocking requirements and detection strategies, are discussed and mitigation measures are proposed.

During summer 2025, the CERN Large Hadron Collider operated for the first time with oxygen and neon ion beams. Three different machine configurations---with collisions of p‑O, O‑O, and Ne‑Ne and with varying beam energies and optics---had to be commissioned and exploited for physics operation during the eight days allocated. This short run was challenging because of its very tight schedule, the novel modes of operation, and new beam‑physics effects such as transmutation of oxygen and neon nuclei into other nuclei with the same magnetic rigidity. In spite of these challenges the run was very successful with the luminosity targets set by the LHC experiments fully met and, in most cases, even exceeded by large factors. In addition, time was allocated for machine studies, resulting in the first LHC data on crystal channeling with O and Ne ions. In this article we give a general overview of the LHC machine configuration, operational challenges, and experience during the run, as well as the achieved performance and the key contributors to the successful outcome. The results demonstrate the LHC’s flexibility for mixed‑species operation and give valuable input for future ion

After every high-energy beam dump event at the Large Hadron Collider (LHC), the beam orbit before the dump, which is collected as part of the high-resolution post-mortem data, is analysed to identify any anomalous behaviour. This analysis is currently performed manually for both beams in both planes. Statistical methods based on post-mortem beam position monitor data from the years 2022-2024 were developed to automate this analysis. This paper shows that the developed methods perform well on LHC beam dump events to automatically identify orbit anomalies of different durations and patterns.

Ethernet-enabled Data Acquisition and Supervision (EDAQ) systems have become the standard platform for commissioning, controlling, and supervising the next generation of Quench Protection Systems (QPS) at CERN. EDAQ-equipped QPS devices have been installed in recent upgrades to magnet test facilities, most notably in the IT-String test facility. This contribution summarizes the operational experience gained during these installations and highlights the key advancements that have enabled the EDAQ ecosystem to mature into a production-ready solution. Notable developments include a configuration validation system, improved error-recovery strategies, over-the-air (OTA) firmware updates, and seamless integration with the full range of HL-LHC QPS equipment. The results of a comprehensive set of performance tests are presented and discussed, confirming that the EDAQ system is ready for deployment as part of the High Luminosity LHC upgrade, for which the installation is to start in the coming years.

The electron-positron Future Circular Collider (FCC-ee) will initially operate at the Z-pole energy of 45.6 GeV with beams composed of 12 000 bunches, storing a total energy of 17.5 MJ per beam. Combined with small emittances, this results in extremely high beam energy densities that pose a significant damage risk to accelerator components. A comprehensive assessment of powering failure scenarios is therefore essential to ensure safe machine operation. This study evaluates the impact of a powering failure in one of the main dipole circuits using the Local Chromaticity Correction (LCC) lattice configuration. Multi-turn bunch tracking simulations are performed to determine the beam response and assess failure criticality. We interpret these novel results with respect to previously established results for the Global Hybrid Correction (GHC) lattice. Horizontal orbit excursions are found to develop over a significantly longer timescale than for the GHC lattice. The underlying physics of this behaviour is analysed in detail, with emphasis on the role of the modified sextupole configuration in the arcs. Based on these findings, the implications for machine protection system design, including interlocking requirements and detection strategies, are discussed and mitigation measures are proposed.

The High-Luminosity Large Hadron Collider (HL-LHC) will increase the nominal LHC integrated luminosity by a factor of 10 and operate with proton beams storing up to 700 MJ of energy per beam. In this upgraded machine, a new quench protection system, the Coupling-Loss Induced Quench (CLIQ) system, will be installed in combination with conventional quench heaters to protect the Nb3Sn inner triplet superconducting magnets. A spurious CLIQ discharge with circulating beams represents the most critical beam-loss-related failure scenario in the HL-LHC era due to the rapid electromagnetic field perturbations it induces. Simulations combining dynamic electromagnetic field maps from a spurious CLIQ discharge with Xsuite beam tracking show that the entire beam can be lost within 4 ms, with critical loss levels, defined as losses sufficient to pose a risk of damage to accelerator components, reached within only a few turns. Both double-Gaussian and q-Gaussian halo profiles are studied, revealing significant sensitivity of beam losses to the tail population distribution. The influence of machine optics is also examined, showing that the baseline round optics provide sufficient safety margin, whereas for the flat optics option this becomes significantly more critical.

The Large Hadron Collider operates with 24 power converter circuits supplying the lattice skew quadrupole magnets for coupling correction. These circuits are currently not interlocked via the Powering Interlock Controller. Recent operational experience shows that a trip of one of these circuits can cause beam losses that can lead to beam dumps via beam loss monitors. This study employs Xsuite beam tracking simulations to assess the impact of individual skew quadrupole circuit failures on beam losses under realistic LHC Run 3 operating conditions. The simulations identify the circuits that were subsequently connected to the beam interlocking system during the 2025 Year-End Technical Stop.

The Quench Detection Systems (QDS) are essential for protecting the LHC superconducting magnets and circuits during quench events. During the upcoming Long Shutdown 3 (2026-2030), several of these systems will undergo major renovation, including those for Individually Powered Quadrupole and Dipole magnets and the Inner Triplets. To secure the continued high performance of machine protection elements, a comprehensive reliability analysis was performed to ensure the probability of critical failures leading to months of downtime meets stringent requirements, while minimizing the impact on machine availability. Different system architectures were evaluated and compared. Optimized architectures were identified and fed back into the design, eliminating Single Points of Failure. Failure probabilities were estimated using analytical models that account for redundancy, inspection strategies, and demand frequencies. Results indicate that the reliability targets can be met both in operation and during magnet training campaigns, with and without additional power supplies, provided that reliable monitoring is in place and reacted upon. Yearly testing of the trigger connection to the quench heaters (DQHDS) is found to be sufficient.

Run 3 represents the final operational phase of the LHC before the transition to the High-Luminosity (HL) LHC era. It covers the operational years 2022 to 2026 and ends just before Long Shutdown 3, starting in July 2026. This period is defined by the successful restart of beam operation following the maintenance and upgrades during Long Shutdown 2, the establishment of a stable operational scheme enabling record-breaking integrated luminosities, and the exploration of performance limits in preparation for HL-LHC. This has all been achieved with infrastructure and equipment soon approaching two decades since first commissioning. Run 3 availability was closely monitored using CERN’s Accelerator Fault Tracking tool, which records fault source, duration, and cross-system impacts. The analysis presented here extracts lessons for HL-LHC from these fault statistics. Machine unavailability is dominated by long-duration faults arising from latent weaknesses, often introduced by recent upgrades and exposed when performance is pushed to its limits. While individual systems require targeted mitigation, there is little evidence of accelerator-wide aging. Radiation-induced faults show a strong impact, demanding specific attention for HL operation. These insights support future strategies for efficient machine exploitation.

The Future Circular Electron-Positron Collider (FCC-ee) is CERN’s leading proposal for the next generation of energy-frontier particle accelerators. At 91 km, it is ambitious in size, complexity and technical objectives. Availability is a significant challenge. Rising to this ambition requires a coordinated availability-driven design strategy. Three broad objectives are identified: (1) R\&D opportunities must be evaluated and compared across holistic metrics to enable early and informed design decisions; (2) Precise and balanced targets for availability must be defined ready for detailed system design; (3) Viable solutions to improve performance must be optimised against cost constraints to deliver efficient as well as performant solutions. Towards these objectives, this paper presents early results from ramilab, an integration-level performance-cost optimisation tool designed to evaluate, compare and optimise accelerator designs in terms of their holistic effect on machine availability and integrated luminosity.

One of the main drivers of integrated luminosity production in the High-Luminosity LHC (HL-LHC) era is the bunch intensity, expected to reach $2.3\times10^{11}$~protons per bunch at injection compared to the maximum $1.8\times10^{11}$ achieved in Run~3 operation. Such high intensities bring significant challenges, in particular localized beam induced heating due to impedance and the associated risk of equipment damage. In that respect, any issue discovered only in Run~4, the first run of the HL-LHC era, could lead to significant downtime or intensity limitations until appropriate mitigation measures are put in place. It is therefore essential to identify such potential limitations to achieve the target intensity before the end of the presently ongoing Run~3. This paper summarizes the preparation steps and strategy foreseen for dedicated high-intensity tests at the end of the 2026 LHC operation, as a last step before Long Shutdown~3 (LS3). The tests aim at reaching and sustaining HL-LHC beam parameters with various HL-LHC beam types, in order to probe impedance-related limits and assess equipment non-conformities, as well as potential design issues and unknown limitations in view of reliable HL-LHC operation. Preparation for the high-intensity tests started with dedicated machine development studies in 2025, making significant progress towards HL-LHC beams and identifying critical devices. Key observations and plans for 2026 are presented.