Science & Environment

LHC restart 'not before Wednesday'

inside CMS
Image caption The four big experiments, spaced around the LHC's tunnels, are awaiting the return of the proton beams

Run Two of the Large Hadron Collider is set to ramp up this week but beams will not go full circle before Wednesday, according to scientists at Cern.

The LHC has been shut down since early 2013, in order for the gigantic machine to be serviced and upgraded.

It is now ready to run at its "design energy" - which means it will smash protons together with nearly double the energies reached during Run One.

But restarting is a gradual process and every step has to be taken carefully.

Scientists working on the LHC's experiments, spaced around its famous 27km circle, now say that because of all the checking that must be done, they are not expecting proton beams until at least 25 March.

This is on schedule, since the notional "restart" - defined by some as beams proceeding, inside their two pipes, all the way around the LHC in both directions - was previously promised for sometime "in the week commencing 23 March".

Hot and cold

Even once the beams are doing complete laps, the teams do not expect to be creating actual collisions for about another two months.

This is not a process that anybody wants to rush.

"It is practically a new machine," said Rolf Heuer, Cern director general, at a press conference last week.

"You have to remember that during the shut down we opened the machine essentially every 20m."

During that maintenance, he added, every single one of the connections between the LHC's 10,000 magnets - which steer the proton beams in a precise circle - was inspected and reinforced, "in order to be rock stable, even if there is a movement of the magnets when they go from cold to warm, or the other way around".

These superconducting electromagnets are chilled to -273C (colder than outer space) in order to do their job.

Inside the beams themselves, on the other hand, things have the potential to get very hot.

"You must be very careful switching on such a high power laser, so to speak, because it has a power which could melt 500 kg of copper - each beam," Dr Heuer said.

"So both beams together - one tonne of copper! We don't want to do that."

Image copyright SPL
Image caption The LHC's beam is steered by nearly 10,000 supercooled, superconducting electromagnets

So the scientists working on the seven major physics experiments (the four biggest ones being Atlas, CMS, LHCb and Alice) must be patient.

They all have different sorts of detectors, many of which have also been serviced and upgraded since 2013, ready and waiting to catch all the subatomic particles that spray out of the high-energy proton collisions. Then comes the immense task of analysing the data to calculate a debris particle's energy, mass and direction - and to see if anything surprising can be revealed.

But before any of this can happen, there must be beams.

"The moment they turn back on, we'll be ready and waiting for them," said Dave Charlton, spokesperson for Atlas.

Follow Jonathan on Twitter

More on this story

Related Internet links

The BBC is not responsible for the content of external Internet sites