Over the past three weeks, deep under the Jura Mountains on the Swiss-French border, a monster has been sleeping. Over Christmas, the Large Hadron Collider, the world’s largest experiment, takes a break from colliding protons together in an underground tunnel. The machine normally runs for 24 hour-a-day, seven days a week, but for four weeks in January and December, it is switched off.
There are several reasons for the extended break. The physicists, engineers and support staff who operate the machine and experiments are human. Yes, they are devoted to the search for the fundamental laws that govern the Universe, but they also like to indulge on Christmas pudding and see their families.
That explains why the LHC doesn’t run on Christmas day, but why does it shut down for three weeks?
Because it’s cold outside.
The cold doesn’t affect how the LHC works – far from it, as the machine is cooled to -271ºC. But it does affect the power supply.
One of the most intriguing facts I’ve learned over the course of working on the Science Museum’s upcoming LHC exhibition is that even though the LHC does an extremely specialised and power-consuming task – accelerating protons so they have the energy of a high speed train and are travelling at nearly the speed of light – the machine takes its power from the French grid. The same nuclear, coal and hydro-electricity plants that provide the energy to light the Mona Lisa and charge your mobile on holiday also power the LHC.
When it’s cold outside French electricity consumption spikes. In December, France uses about 50 percent more electricity than it does in August, heating, cooking and lighting dark days. When all systems are go, CERN can use as much as a third of Geneva’s power, or the same as a large town. So during darkest depths of winter, when the French grid is being stretched the most, the LHC powers down.
The time off isn’t wasted. Repairs and upgrades are always needed, so engineers have been busy tweaking to ensure the LHC is in tip-top condition for its run in 2013. From next week LHC will fire protons into lead nuclei for a month. After that short run, the machine shuts for two years for a serious upgrade.