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ALICE and CMS line up the final big pieces underground

22 February 2008

With the completion of two major installation projects, nearly all the infrastructure for the ALICE experiment is now in place in the cavern at Point 2 on the LHC ring, near St. Genis-Pouilly in France. Further round the ring, at Point 5 near Cessy, the final large piece has descended into the cavern for the CMS detector, which is the first of its kind to have been constructed above ground before being lowered piece by piece into the cavern below.

In the ALICE cavern, the electromagnetic calorimeter support structure and "mini" space frame – the device for connecting service networks to the inside of the detector – went into position at the end of 2007. At 7 m high and with a weight of 30 tonnes, the calorimeter support structure consists of two austenitic stainless steel "half-shells", welded and bolted together to give the structure its specially designed curved form. Once the calorimeter is in place, the support will have to bear nearly three times its own weight.

Lowering the structure and positioning it within the ALICE detector constituted major technical challenges for the ALICE installation team, who made numerous preparatory tests, and had to dismantle two walkways to free up the passage into the cavern. They then inserted the structure inside the detector, sliding it in between the face of the magnet and the metal space-frame that bears detector systems in the centre of ALICE. At one point there was a clearance of only a couple of centimetres between the moving structure and the magnet.

Two weeks later, the final big piece of the jigsaw went into place – the "mini" space frame, which resembles a giant socket outlet and weighs 14 tonnes. The device is almost 10 m long and carries all the supply cables for the services required for detector operation (gas, water, electricity, signals). Sitting straight across from the magnet, it connects the inner detector with the outside world.

Around the LHC ring at Point 5, the CMS Collaboration has celebrated the descent of the 15th and final large element of the detector into the experiment’s cavern (see CMS starts underground). Weighing 1430 tonnes and asymmetrical in shape, the end cap designated YE+1 is the largest of the three pieces that form one end of the detector. After the lowering operation, the piece was temporarily stowed as far as possible from the central components to leave room to cable the central tracker (see CMS installs the world’s largest silicon) and install the beam pipe.

Once these components are all in place CMS will be almost ready. All that will remain will be to seal all the components of the detector, and perform the final tests with cosmic rays and the magnet fully powered to 4 T.

For a video of the final lowering operation for CMS, see http://cdsweb.cern.ch/record/1083427.

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