CERN Just Went Dark — What's Still Growing Inside the Collider Is a Total Nightmare

On 29 June 2026, CERN switched off the Large Hadron Collider for four years. The machine is now warm, silent and being taken apart for the High-Luminosity LHC upgrade. But something inside the beam pipe did not stop when the beam did.

In the hottest sections of the collider, CERN scientists found the copper had changed: its protective carbon layer stripped away, the metal oxidised into black cupric oxide. That surface feeds an electron avalanche that dumps heat into the magnets' helium. After the last shutdown it got worse, and a 2025 review states the degradation is not compatible with the beam the upgrade was built for.

We also look at the dust "UFOs" that have dumped the beam more than a hundred times, the unidentified object lying inside the pipe near Point 8, and a June 2026 proposal that some of those events could be caused by dark matter. That last idea is a hypothesis, not a detection, and we treat it that way.

SOURCES
CERN enters Long Shutdown 3: https://home.cern/cern-bids-farewell-to-the-lhc-and-enters-long-shutdown-3/
Long Shutdown 3 overview: https://home.cern/science/long-shutdown-3/
LHC warm-up to room temperature: https://home.cern/the-lhc-is-being-warmed-up-from-near-absolute-zero-to-room-temperature/
The Third Long Shutdown of the CERN accelerator complex (IPAC): https://inspirehep.net/files/633da3a07160bd5620edbdae18a9f120
Petit et al. (2021), Beam-induced surface modifications as a critical source of heat loads in the LHC, Communications Physics: https://www.nature.com/articles/s42005-021-00698-x
Origin and mitigation of the beam-induced surface modifications of the LHC beam screens: https://www.researchgate.net/publication/367323672_Origin_and_mitigation_of_the_beam-induced_surface_modifications_of_the_LHC_beam_screens
LHC operation and the High-Luminosity LHC upgrade project (2025): https://arxiv.org/abs/2505.03535
First series beam screen for the HL-LHC with amorphous carbon coating: https://hilumilhc.web.cern.ch/article/first-series-beam-screen-hl-lhc-amorphous-carbon-coating
Selective laser processing of accelerator beam screen surfaces: https://pubs.rsc.org/lf/article/2/2/521/853532/Selective-laser-processing-of-particle-accelerator
Characterising the surface resistance of laser-treated LHC beam screens: https://arxiv.org/abs/2502.01392
Dynamics of the interaction of dust particles with the LHC beam, Phys. Rev. Accel. Beams: https://link.aps.org/doi/10.1103/PhysRevAccelBeams.23.124501
LHC report, the unidentified lying object: https://home.cern/news/news/cern/lhc-report-intensity-ramp-familiar-demons
Liang & Zhitnitsky (2026), Unidentified falling objects in the LHC as dark matter signals: https://arxiv.org/abs/2602.10562

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