The Large Hadron Collider shut down for summer on 1 Nov 2023.
This is a yearly thing, to make sure that Europe has enough electrical power to run air conditioning through summer.
The method of shutdown is/will_be to fake an emergency. You may remember in the dim distant past when the Large Hadron Collider melted shortly after first start up. One electrical connection overheated which caused the superconducting magnets to lose their magnetism, which threw to electrical load onto the next superconducting magnet etc. until a major sector was permanently out of action. The LHC was shut down and repaired, followed by an upgrade to the other sectors in the next shut-down. These upgrades were tested at the time.
This time, they’re deliberately going to create the same type of emergency to test the emergency shut-down procedure.
The method is quite tricky. https://www.home.cern/news/news/accelerators/accelerator-report-ending-2023-run-quench
“During lead-ion collisions, the aim is to collide the ions head on. However, not all the ions collide: some just pass close to each other. In this case, the electromagnetic interaction between the ions is very strong and can lead to the production of electron–positron pairs, in which the electron binds to the lead nuclei, changing the Pb82+ lead ions into Pb81+ lead ions.
“These Pb81+ ions have a different electrical charge to the Pb82+ ions. Therefore, within the magnetic field of the same LHC magnets, they are deflected on a different trajectory, separate from the main Pb82+ beam, forming a secondary beam. The trajectory of this secondary beam is so different that it is quickly lost, in a well-defined location in the machine, where it deposits its energy.
“To prevent this Pb81+ beam from being lost in a magnet, extra corrector magnets are used to create a local orbit bump that displaces the beam locally by about 3 mm, thus changing the location where it is lost, so that its energy is deposited in a collimator, which is specifically designed to absorb these ions and their energy.
“At midnight on Sunday, the LHC machine experts will fill the machine as normal. However, this time they will change the local orbit bump value so that the Pb81+ beam is deposited in a superconducting magnet instead of a collimator.
The superconducting magnet heats up, loses its magnetism and the emergency system kicks in shutting the LHC down.
You may have noticed in the above, the mention of beams of lead ions. The proton-proton collisions were terminated at the end of August 2023. Full results are still pending. The LHC switched to lead-lead ion collisions starting 1 September 2023. So the ATLAS and CMS detectors can take a rest, and the ALICE detector takes centre stage. ALICE stands for “A Large Ion Collider Experiment”. https://www.home.cern/news/news/accelerators/accelerator-report-getting-lead-ions-ready-physics
“ALICE (A Large Ion Collider Experiment) is a detector dedicated to heavy-ion physics. It is designed to study the physics of strongly interacting matter at extreme energy densities, where a phase of matter called quark-gluon plasma forms.
“Lead ions are “born” in the source of Linac3, where a pure lead sample is evaporated: oxygen gas and lead vapour are injected into the source plasma chamber. A microwave is applied to create the plasma in which the lead and oxygen atoms are ionised. These ions are then extracted, partially stripped and accelerated. The lead-ion charge after the stripping process is 54+, meaning that 28 of the 82 electrons have been removed (a lead atom originally has 82 electrons).
“After an initial acceleration in the SPS, the beam is slip-stacked to reduce the bunch spacing to 50 ns, thus doubling the total lead-ion beam intensity in the LHC. Following a final acceleration phase, the beam is extracted and injected into the LHC, either in a clockwise or counter-clockwise direction. The LHC will be filled with up to 1248 bunches per beam.
“momentum slip-stacking involves injecting two batches of four lead-ion bunches separated by 100 nanoseconds to produce a single batch of eight lead-ion bunches separated by 50 nanoseconds. In this process, the 56 bunches injected into the SPS are divided among two RF systems, which each receive 28 bunches. As there is a small frequency difference between these two RF systems, half of the beam travels slightly faster along the SPS circumference (known as “slipping”). Once the two halves of the beam are placed so that the space between two bunches is 50 ns, the beam is interleaved (or “stacked”). This allows the total number of bunches injected into the LHC to increase from 648 in Run 2 to 1248 in Run 3 and subsequent runs.
Slip stacking was not without its problems, particularly the generation of a background noise signal at half the injection frequency. https://www.home.cern/news/news/accelerators/accelerator-report-optimisation-greater-success-and-new-challenges. “beam losses during the last part of the acceleration ramp, causing the beam to be dumped, and a high level of background noise in the ALICE detector, in an area where the circulating beam interacts with the collimators.”
From an initial 1% background noise from this process, tweaking the system reduced that noise to 0.02%.
I seem to have misplaced several other CERN LHC news articles. There have been two other things of note.
One is that in addition to the attempted creation of a quark-gluon plasma, the LCH will be using slightly offset lead ion beams to investigate two other phenomena.
Another piece of news that I saw was a brief note about the search for dark matter. Two different types of dark matter have been investigated by the LHC. One is axions and “axion like particles”. A second is “dark photons” generated by “hidden sector” supergravity and string theory models. Both have recently been ruled out, within the energy limitations of the machine.
https://cds.cern.ch/record/2853210/files/CERN-FASER-CONF-2023-001.pdf
“FASER is an LHC experiment designed to search for light, weakly-interacting particles
that are produced in proton-proton collisions at the ATLAS interaction point and travel in
the far-forward direction. The first results from a search for dark photons decaying to an
electron-positron pair, using a dataset corresponding to an integrated luminosity of 27.0 fb^−1
collected at center-of-mass energy √s = 13.6 TeV in 2022 in LHC Run 3, are presented. No
events are seen in an almost background-free analysis, yielding world-leading constraints on
dark photons with couplings ϵ ∼ 10^−5 − 10^−4 and masses ∼ 10 MeV − 100 MeV.”
https://link.springer.com/article/10.1007/JHEP09120
“In the presence of axions or axion-like particles (ALPs) that couple to the
Standard Model via dimension-five interactions, dimension-six SMEFT interactions are
generated via renormalization-group evolution. As many of these SMEFT contributions
are experimentally tightly constrained, this “ALP-SMEFT interference” can be used to
derive indirect bounds on the ALP couplings to the Standard Model particles. We present
a global analysis of the Wilson coefficients of the ALP effective Lagrangian based on Higgs,
top, and low-energy data. The obtained bounds are model independent and are competitive
or even stronger than direct bounds in the GeV to TeV ALP-mass range.