From the BBC News site:
[I]Engineers injected the first low-intensity proton beams into the LHC in August. But they did not go all the way around the ring. On Wednesday [today], they sent a proton beam around the full circumference of the LHC tunnel.
Technicians had to be on the lookout for potential problems: “There are on the order of 2,000 magnetic circuits in the machine. This means there are 2,000 power supplies which generate the current which flows in the coils of the magnets,” Steve Myers, head of the accelerator and beam department, told BBC News.
If there was a fault with any of these, he said, it would have stopped the beam. They were also wary of obstacles in the beam pipe which could prevent the protons from completing their first circuit.
Mr Myers has experience of the latter problem. While working on the LHC’s predecessor, a machine called the Large-Electron Positron Collider, engineers found two beer bottles wedged into the beam pipe - a deliberate, one-off act of sabotage.
The culprits - who were drinking a particular brand which advertising once claimed would “refresh the parts other beers cannot reach” - were never found.[/I]