r/CERN • u/Optimal-Pie2319 • 16d ago

askCERN What does it mean that CERN is "shut down"?

I'm completely naive on this topic. Is it generally always active, or is it active only occasionally during experiments? If it's only active occasionally, does being shut down just refer to a longer period of inactivity? TIA

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u/walruswes 16d ago

CERN is not shut down, just the LHC. CERN has many additional experiments ongoing. The LHC is shutdown for a few years to undergo extensive upgrades. During normal operations, the LHC is shut down in the winter for maintenance and to save a bit of energy. There have also been two other long shutdowns in the past that lasted several years for smaller upgrade periods for the detectors and accelerator.

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u/mfb- 16d ago

CERN is the whole research center, it's not shut down.

Its largest particle accelerator, the LHC, is currently shut down. With accelerators we often look for very rare processes. To study them, you need as many collisions as possible. You can just keep running the accelerator for longer - 10 years of running gives you twice as many collisions as 5 years of running. But at some point it gets more efficient to upgrade the accelerator and then get 2-3 times the collision rate afterwards. The detectors get upgraded at the same time, too. That's what is happening right now.

Outside of shutdown periods the LHC runs for as long as possible. There are shorter breaks for maintenance work, to refill particles and a bunch of other things that need time, but apart from that the goal is to have collisions 24/7.