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This is the beam switch in the LHC control room at @CERN. If something goes wrong, this lets controllers “dump” the proton beam by spreading it out and slamming it into a concrete-encased graphite composite cylinder. Every unplanned dump costs CERN about a million dollars. 
During my visit, the proton beam was already off, but they still didn’t let me touch the beam dump switch. I got close though! 😁 Thanks to accelerator physicist @AndreaStmaria for taking the time to show me around (and for resisting tackling me when I approached the switch)!
More on Large Hadron Collider proton beam dumps, and how they have to spread the beam out first because “in its compressed form it would drill a hole tens of meters long in any material” 😧 symmetrymagazine.org/article/decemb…
Because people have asked… the bottles along the walls in the control room are from celebrations of certain milestones in the project, like “First W [boson]” or “First top [quark] candidate.” The celebrations don’t happen while the beam is circulating! There are also memes 😂
A follow up on this tweet: I've been told by other CERN folk that the $1m number I was given is too high. I don't know what the official accounting is (I've asked; no answer) but it seems to depend a lot on how you count labor as well as time & electricity
Suffice it to say, though, it's not a switch anyone hits without a VERY good reason.
