News from the pit

4 February 2008

The small wheels last month

The small wheels are small in name only. At 9.3 metres in diameter, and weighing in at 100 tons each, moving them from Building 191, at the north-west tip of the Meyrin site, to the Cavern next week is going to be a challenge which is anything but small.

"We’ll be using a specialist truck from a company called Friderici," says George Brandenburg (Harvard/CERN).  "It has 128 wheels, partitioned into 16 smaller trucks of eight wheels. Each one of these is individually steerable using hydraulic controls, so it can be lifted up and down, and the whole bed can level itself and go around any kind of corner. Regardless of what the street is doing, it’s important we keep the truck bed flat!"

The small wheels, designed and built by collaborators from CERN, China, Israel, Japan, Russia and the USA, carry three chamber technologies: Thin Gap Chambers (TGC), Monitored Drift Tube chambers (MDT), and Cathode Strip Chambers (CSC). They are the final two pieces of active detector yet to be installed, and have been under furious construction in Building 191 for the last few months.  The detectors are supported and protected by the disk shielding that was constructed in the same building prior to the Small Wheels. This shielding structure was designed and produced by a team in the ATLAS Technical coordination group, with a large contribution from Serbian, Armenian and Pakistani collaborators (see enews May 2007).

"This was the only building in the whole of CERN which was large enough for us to do our work, so we had to wait until the end cap toroid magnet was finished before we could move in," says US ATLAS Muon Manager, Frank Taylor. "We put the CSC and MDT chambers on the small wheels over the end of the summer and fall, and we finished the installation of the second wheel, including the TGCs, just before Christmas."

The wheels have now been fully tested with cosmic rays, and are ready to be transported on February 8th, using the transport frame that can be seen on the left-hand side of the photograph above. Vincent Hedberg  and his two engineers, Patrick Petit and Jan Palla of the shielding team will be responsible for the move. “Jan has spent years designing and building that transport frame,” says Vincent. “While Patrick is the floor manager of building 191. He has been instrumental in organising all of the work, from the big things like putting the frame onto the small wheel to a million little things like the purchasing of tools and equipment. We are now almost ready to go and it will be the result of years of work and planning for us when the disk shielding with the small wheel are finally in ATLAS."

The hydraulic truck beds carrying them to Point 1 will be controlled by computer, and fine-tuned via laptop in real time by an expert who will sit on the back of the truck with the load. In addition to these high-tech methods of keeping the all-important pieces levelled, some good old fashioned techniques will be employed as well: A plumb-bob and circle will be monitored by a man on the ground, just to ensure the computers are doing their jobs properly.

Frank expects the transport from B191 to Point 1 to be "quite a parade – but an uneventful one we hope". Although the truck will be travelling at walking speed when it is in motion, the company will be stopping it frequently to make small adjustments, consult one-another, and close off parts of the road ahead. The journey is expected to take several hours, and will involve the wheels travelling the length of the southern perimeter road, through the centre of the Meyrin site, and out across the road at Entrance B.

The entire procedure of loading, transporting, unloading, and finally lowering each wheel into the pit is expected to take five days. The whole operation, then, ought to take around eleven days, with the second wheel setting off six days after the first.

"It will be a heart-throbbing few days. I think I’ll take Vallium on the mornings of the moves," jokes Frank. "We all will. And we’ll have to have champagne in the evening, after the last one goes!"

Colin Barras


Ceri Perkins