The last pieces of the puzzle

Like the last pieces of a giant jigsaw puzzle, the final components of the titanic Large Hadron Collider (LHC) experiments at CERN are slotting into place. At ATLAS, CMS, ALICE and LHCb the remaining large pieces of equipment are being carefully lowered into the caverns in preparation for the start up later this year of the most powerful particle accelerator ever, the LHC. 

At CERN, 100 metres underground in the countryside outside Geneva, the LHC and its four big experiments are stuffed full of some of the most complex scientific apparatus in the world. On the surface the assembly hangers are beginning to look eerily empty, but below a vision of mind-boggling complexity is now almost fully formed.

Manoeuvring the pieces, sometimes weighing hundreds of tonnes each and measuring several metres in diameter, is a formidable challenge.  The huge parts have to be manipulated in very confined spaces, often with only a few centimetres of clearance on either side of the cavern shaft.

This month the final two large pieces of the ATLAS experiment, the “small wheels”, will be lowered into the underground hall. Although called the “small wheels” they are in fact 10 metres in diameter and weigh 140 tonnes. However, they are dwarfed by ATLAS’s other eight enormous wheels, 25 metres in diameter, which were lowered last year.  All have the same goal - to track particles called muons. When operating they will have the ability to track these particles to within the width of a human hair.

In January the last of the 15 detector “slices” of the CMS experiment - an enormous disk 15 metres in diameter and weighing 1430 tonnes - was spectacularly lowered onto the floor of the CMS cavern (see video). This spectacle was the last in a procession of events to lower each of the layers of CMS into place 100 metres under ground. CMS is the first experiment of its kind to be constructed above ground and then lowered, element by element, to the cavern below.

At ALICE the end is also in sight. All the heavy infrastructure has been in place since December 2007, when the 30-tonne electromagnetic calorimeter support structure and the 14-tonne “mini” space frame which connects the service networks to the detector were put into place in the cavern. 

The next few weeks will be an emotional time at CERN. The product of some 15 years of work is coming to fruition and tensions are riding high as the equipment is tested. Soon, the first protons will be smashed together and the secrets of our universe will begin to unravel.

22 February 2008