system
Given the following post, respond as if you're commenting on Reddit:
human
How long is the LHC at CERN on for at a time? How long does it take before a test will be done?

Does it take a long time to actually charge up? Somebody told me it’ll take months before anything actually happens after they turn it on today, but I wanted to ask here if that’s how it works.
gpt
The ideal long-term running plan has ~10 hours of non-stop collisions followed by 2-3 hours of dumping the remaining particles, ramping down the magnets, preparing for a new fill, filling in particles, accelerating/ramping up magnets, and preparing the beams for collisions.

You can't fill in more protons once they have been accelerated, so over time the number of protons and therefore the collision rate decreases. The 10 hour number is the approximate point where it's better to accept the 2-3 hours downtime in exchange for going back to the initial high collision rate again. That gives us about two fills per day and collisions ~70-80% of the time.

The LHC has tons of components that all can have some issues, so realistically the time between collisions is often a bit longer, and sometimes these problems can stop collisions, so in practice the fraction of time with collisions is lower - something like 30-50%. That also means fills are often kept for longer than 10 hours if possible, because we know the average time to the next collisions is higher than the optimum.

Looking at a longer time frame: Every winter there is a shutdown for maintenance, smaller upgrades and so on. After that the machine parameters need to be tuned again. That means the accelerator starts with very low beam intensities to be on the safe side. After a long shutdown (e.g. like this year) it's even worse because many components are new and the operators have to make everything work together. Establishing collisions, stable beam parameters, and going to higher beam intensities takes a few months, followed by a few months focused on data-taking (with some time spent on pushing towards even higher collision rates). We already had some initial collisions, but only at a low rate and with parts of the detectors still switched off. The plan for today is collisions with all detectors fully switched on, i.e. the start of physics data-taking. The collision rate will still be very low.