News from the pit

21 April 2008

A schematic of the detector used by the closing planning team

It has been five years in the making, but the installation phase of ATLAS is almost over, as all the LHC detectors begin the final countdown to switch-on day by moving into their closing configurations.

“We’re trying to optimise the sequence and train all the technicians so they understand what we’re trying to do,” said Miikka Kotamaki, who has been responsible for developing the schedule for the final closing. “If needed, we can also work overtime during weekends and holidays. But all this depends ultimately on the LHC; the green light from the LHC – which we expect to pinpoint the end of May as a final date – means we have to start closing. We’ll have to push hard, but I think we will be able to do that.”

Speaking to e-News several weeks ago, Miikka was working with the start date of April 18th for the beginning of the ATLAS closing operation, but the discovery of two small leaks in the Pixel cooling system on Tuesday has meant that the schedule has had to be pushed back by six days. “We’ll start the closing operations on the 24th, roughly one week late with respect to our baseline schedule,” said Miikka on Thursday, explaining that they may take advantage of the three official CERN holidays in May to recuperate a few days, if necessary.

Internally, the team had been waiting for the go-ahead from the Pixel detector, which, having had all its services connected, has been undergoing final commissioning procedures over the last few weeks. Once this is out of the way, they’ll begin an elaborate six-week long dance of components that has been carefully calculated to finish in time for the LHC’s predicted closing date at the beginning of June.

Those who have seen the detector recently will know that there are currently gaps between the barrel and endcap calorimeters; the calorimeters and the small wheels; the small wheels and the endcap toroid magnets; and the endcap toroids and the big wheels. The initial closing will take place in two stages, with the first incorporating moving the endcap calorimeter inwards and testing bakeout equipment which removes any residual water vapour from the beam pipe. The second stage will see the endcap calorimeter moved into place, and the whole process will then be repeated on the other side of the detector.

By this point, there will be no more access to the inner detector or the calorimeters. The beam pipe at each end will be eased out of the endcap toroids and connected to the pipes protruding from the closed part of the detector in the centre of the cavern. After a phase of testing, the endcap toroids will be moved into position against the barrel, and, one side at a time, four of the five structures of each of the big wheels will be brought up against the toroids, to allow access to the fifth big wheel structures, fixed against the cavern walls.

With the detector in this position, some final muon detecting sectors will be added to the fifth wheels and connected up, before the four other structures are moved back towards the cavern walls to make way for the final sections of the beam pipe to be installed at either end. These will then be carefully fitted with radiation shielding made of steel and concrete.

This configuration should be achieved by the end of May, but as soon as the endcap toroids are in place, magnet testing at full power will need to begin in parallel with the closing activities. For safety reasons, this will take place during the nights when no-one is in the cavern, and closing will continue in earnest during the day.

“It’s very tight, but it’s feasible,” said a confident Miikka. “With the schedule we have at the moment, we haven’t had to use any shifts and I haven’t scheduled any weekend work, so we have a bit of room to breathe.”


Ceri Perkins