LHC TimerCountdown to the Large Hadron Collider restart
T-minus to first HL-LHC beams · target June 2030 · exact day TBC by CERN
When Does the LHC // Restart?
The Large Hadron Collider restarts in June 2030, when CERN plans first beams in the upgraded High Luminosity LHC. The machine has been shut down since 27 June 2026, when Run 3 ended and Long Shutdown 3 began. This timer counts to the target CERN has published; the exact day is still to be confirmed.
That is the entire job of this site: one date, tracked honestly. Around it, our guides explain why the machine went dark, what it is being turned into, and what happens when it wakes up.
The Machine // What Is the LHC?
The Large Hadron Collider is the most powerful particle accelerator ever built: a 26.659 kilometre superconducting ring roughly 100 metres beneath the border of France and Switzerland. Two beams of protons circulate in opposite directions at 99.999999 percent of light speed and collide inside four detectors, recreating in miniature the energies of the universe's first instants.
Its 1,232 dipole magnets run colder than outer space, at 1.9 kelvin, and its collisions produced the discovery of the Higgs boson in 2012. Since 27 June 2026 the beams are off while the machine is rebuilt. The full tour is in how the LHC works.
The Upgrade // High Luminosity LHC
Long Shutdown 3 is not maintenance. About 1.2 kilometres of the collider is being dismantled and rebuilt with niobium tin focusing magnets, crab cavities and new superconducting power links, while ATLAS and CMS replace entire tracking systems. The goal is luminosity: the upgraded machine will produce collision data roughly ten times faster over its lifetime, targeting 3,000 inverse femtobarns by around 2041.
More data is how you measure the Higgs boson's interaction with itself, catch decays too rare for the original machine, and stress test the Standard Model until something gives. The details live in the HL-LHC guide and the luminosity explainer.
The Roadmap // 2026 to 2030
- Jul 2026LS3 begins. Warm up of 36,000 tonnes of cryogenics; dismantling starts around ATLAS and CMS.
- 2027 to 2029HL-LHC hardware installed: inner triplets, crab cavities, superconducting links, new collimators. Detector rebuilds run in parallel.
- Mid 2028Injector complex restarts, recommissioning beams two years ahead of the ring.
- 2029 to 2030Cooldown to 1.9 K and hardware commissioning: every circuit tested to full current before beam.
- Jun 2030Target: first HL-LHC beams. Commissioning, then Run 4 physics at 14 TeV. The moment this timer exists for.
The complete history from 2008 to 2041 is on the timeline page.
Guides // Learn the Machine
Quick Answers // LHC FAQ
When does the LHC restart?
CERN targets June 2030 for first beams in the upgraded High Luminosity LHC. The exact day has not been announced yet; our countdown tracks mid June and will switch to the precise date when CERN names one. Physics collisions for Run 4 follow first beams after a commissioning period.
Why is the LHC shut down right now?
The collider entered Long Shutdown 3 in early July 2026, a planned four year stop to install the High Luminosity upgrade. About 1.2 kilometres of the machine around the ATLAS and CMS collision points is being rebuilt with new magnets, crab cavities and detector systems.
When did Run 3 end?
The final protons of Run 3 circulated on 27 June 2026, closing a run that began in July 2022 and delivered more collision data than the first two runs combined, at a record energy of 13.6 TeV.
What is the High Luminosity LHC?
An upgraded LHC designed to produce collision data roughly ten times faster over its lifetime, targeting about 3,000 inverse femtobarns by around 2041. Collision energy rises only slightly; the transformation is in the collision rate.
Is the LHC dangerous?
No. Cosmic rays strike Earth's atmosphere at energies far beyond the LHC's and have for billions of years without harm, and CERN's independently reviewed safety assessments concluded the collider presents no danger. Nearly two decades of operation have confirmed it.
How big is the LHC?
The ring is 26.659 kilometres around, buried about 100 metres beneath the border of France and Switzerland near Geneva. It uses 1,232 superconducting dipole magnets, each 15 metres long, kept at 1.9 kelvin.
All twelve questions are on the full FAQ page.
Glossary // Speak Collider
- Luminosity
- The measure of a collider's collision producing intensity. Higher luminosity means more collisions per second and faster accumulation of data. The HL in HL-LHC.
- Integrated luminosity
- Luminosity summed over time; effectively the size of the dataset, measured in inverse femtobarns. The HL-LHC targets about 3,000 fb-1, ten times the original LHC total.
- Femtobarn
- A unit of cross section equal to 10^-43 square centimetres. Its inverse (fb-1) measures integrated luminosity; one fb-1 corresponds to roughly 10^14 proton collisions.
- TeV
- Tera electronvolt, a trillion electronvolts. The LHC collided protons at 13.6 TeV in Run 3 and targets 14 TeV in Run 4. Roughly the kinetic energy of a flying mosquito, concentrated into a single proton.
- Higgs boson
- The particle discovered at the LHC on 4 July 2012, the quantum of the field that gives elementary particles mass. Measuring it precisely is the centrepiece of the HL-LHC programme.
- Higgs self coupling
- The interaction of the Higgs field with itself, probed by producing pairs of Higgs bosons. Too rare for the original LHC; a flagship goal of the high luminosity era.
Twenty six terms defined on the full glossary.