The 2024 LHC run was outstanding in every respect, achieving record-breaking performance in both the proton and the lead-ion runs.
For the proton run, the overall machine availability was excellent, reaching 72.1%, with a record 53.6% of the time spent in collisions. The integrated luminosity for proton physics during Run 3 so far stands at an impressive 196 fb⁻¹, surpassing the combined totals of Runs 1 and 2 - and Run 3 is far from over, with 2025 and 2026 still ahead of us.
The 2024 lead-ion run was equally successful. Issues encountered in 2023 were resolved, enabling 1240 bunches per beam, spaced 50 nanoseconds apart, to collide, with good luminosity production. This performance was further boosted by slightly higher-than-usual bunch intensities delivered by the injectors. The machine's availability during the lead-ion run reached an impressive 75%, with 42% of the time spent in collisions. The lower collision time for lead ions is expected, as the beams typically remain in collision for around 6 hours, compared to about 10 hours for protons. Additionally, the process of filling the LHC with lead ions takes longer than filling it with protons.
Overall, the 2024 run has set a remarkable standard and is testimony to the excellent work done by all the teams working on the LHC and its injector complex.
Several machine development (MD) studies were planned for the final hours of the 2024 run. The last of these MD studies aimed to create an increasing and well-controlled lead-ion beam loss into a superconducting magnet until it quenched. This would provide valuable insights into the threshold of beam losses that a magnet can tolerate before quenching, serving as a benchmark for past simulations. Such experiments are typically reserved for the end of the annual run to avoid affecting physics operations too much, as the cooldown time required after a quench would otherwise interfere with scheduled experiments.
Unfortunately, at 6.35 a.m. on 23 November, two days ahead of the scheduled end of the 2024 run, the LHC beams were dumped by unintentional magnet quenches, prematurely ending the run.
Beam losses generate neutrons, which can disrupt nearby electronics in what are known as single event upsets (SEU). In this instance, the beam loss disrupted the quench protection system electronics (QPS), which then triggered the heaters located in the superconducting magnets, causing them to distribute the heat evenly along the magnets concerned and thus avoid damage. An unprecedented number of magnets - 23 dipoles and two quadrupoles - quenched, dissipating approximately 110 MJ of stored energy.
In the late afternoon of 24 November, the cryogenics system successfully restored the temperatures of the quenched magnets. The magnet circuits were then repowered so that their integrity could be assessed. While initial observations indicated that the circuits were functioning correctly, it was too late to resume physics operations. A thorough analysis by experts is still under way to confirm the circuits' condition.
Engineers and technicians will now begin a busy programme of preventive and corrective maintenance activities in the LHC tunnel. We expect to inject beam again on 5 April for what will hopefully be another successful year.
Much of the injector complex is still running and will be switched off at 6 a.m. on 2 December. More on this in my last report of 2024 … stay tuned!
| What is a magnet quench, how is one triggered and how do we deal with it? A superconducting magnet quench occurs when a superconducting magnet transitions from its superconducting state to a normal resistive state, losing its ability to conduct electrical current without resistance. A quench is typically triggered by a localised energy deposition, such as heat induced by beam losses, mechanical stress, etc. Superconducting magnets are equipped with quench protection systems (QPS) that measure the voltage across the magnet terminals and can fire heaters to evenly distribute the heat along the magnet and safely dissipate energy in order to prevent localised damage. |
