How to Stop a Runaway Train

The LHC is pretty awesome. It takes a tiny beam of protons, whips them around a proton-sized racetrack at 99.9999% of the speed of light, and smashes them against each other.

But did you ever stop to wonder what happens to those protons when the scientists are done playing with them? That tiny beam of protons, whipping around the proton-sized racetrack at 99.9999% of the speed of light, has 312 megajoules of energy – as much energy as a runaway bullet train.

So how do you stop this runaway bullet train? (Assume Keanu Reeves is unavailable.)

You fire it into one end of a gigantic pencil lead.

It’s called a “beam dump“. It can be made of all sorts of things, but anything that can absorb massive amounts of heat and light without melting will do – and graphite, thanks to its low density and high heat conductivity, is a great candidate.

The real killer when you’re trying to dump a proton beam (this also applies to laser beams) is heat – so if you used something dense and not-particularly-heat-conductive like lead, the front of the beam dump would melt from all of the excess heat. And then the middle would melt, and then the back would melt, and then you’d have to jump out of the way.

With a graphite heatsink (and some clever beam scattering, so that it doesn’t act so much like a laser death ray), some parts are heated to 750 degrees, but it won’t melt – and after a short cooldown period, you can use it all over again.

If you’re interested, here’s a big ol’ research paper that explains all of the LHC’s protection systems.

Or if you’d just like to know whether the LHC has destroyed the world yet, take a look at

And here’s the obligatory xkcd comic about the LHC. This could be our last night on earth!

This entry was posted in Handy. Bookmark the permalink.

2 Responses to How to Stop a Runaway Train

  1. Si says:

    The real question is: how does the amount of energy in the LHC compare to say, an atomic bomb?

  2. Josh says:

    An atomic bomb packs somewhere in the ballpark of 10^14 joules of energy.
    The LHC’s atoms only have about 3*10^8 joules of energy… so it’d take about 30,000 LHCs to equal one Hiroshima.
    Which I guess means the LHC is relatively safe.

Comments are closed.