Some of the first protons to be accelerated inside the Large Hadron Collider smashed into an absorbing device called a collimator at near light speed, producing a shower of particle debris recorded in this image. About an hour later the beam completed a full circuit of the 27km tunnel, to cheers from physicists CERN

Protons have made their first complete lap of the world’s most powerful accelerator to cheers and high fives from assembled physicists.

At 1025 (local time) scientists sent a single beam of protons in a clockwise direction around the full 27 kilometres of the Large Hadron Collider at the CERN laboratory near Geneva, Switzerland.

The journey began at 0930 when LHC project leader Lyn Evans and his team launched protons into the ring. Progress was made in short steps of a few kilometres, so that physicists could learn how to steer the beam, which is travelling at 99.9998% the speed of light.


Steering particles

The LHC’s tunnel is filled with devices called collimators, which steer the beam every few kilometres. Evans and his team opened the collimators one by one when they were sure that they could steer the protons precisely.

The machine worked better than anyone expected. It took only 55 minutes for physicists to steer beams around the full 27km, and the LHC worked on its first go, far better than anyone dared to hope.

Earlier Evans said that he did not know how long it would take his team to circulate the beam.

“It took us 12 hours to circulate a beam around the Large Electron Positron Collider,” says Evans. The LEP Collider was the LHC’s predecessor that was shut down in 2000.

Giant freezer

Physicists working on two of the giant experiments – CMS and ATLAS – have seen sprays of particles in their detectors as protons smashing into the collimators next to the detectors (see image, top right).

The day was not without its dramas, however. During the night, part of the cryogenic system that keeps the ring chilled to 1.9 kelvin (just above absolute zero) failed.

The ring has to be cold for the powerful magnets to work. Physicists managed to fix the problem overnight and started the day’s tests on schedule.

Evans hopes initially to circulate the beams many times in the clockwise direction. The team will attempt to repeat the test later today, but sending protons around in the opposite direction.

However, it will be several weeks before physicists accelerate two proton beams travelling in opposite directions to their full energy of 7 teraelectronvolts, and smash them head on.

The Large Hadron Collider – Find out more about the world’s biggest experiment in our special report.