Bringing Low the Giants

At ALEPH, counting rooms removed all in one go

Jean-Paul Fabre, technical coordinator at ALEPH:'After making safe the structure, the first step was to remove the wiring and cables. Some 210 cubic metres were brought out. Then the counting rooms all round the detector were taken out. They were brought up from the cavern all in one go, up through the shaft, which is 10 metres wide and 150 metres deep. They made it with 15 centimetres to spare. They have been emptied of their contents on their arrival at the top and handed over to the scrap dealers. With that done, the detector has been removed to its parking position at the other end of the underground hall. Dismantling it can now commence. We are going to start with the sub-detectors close to the beam pipe, the internal tracking detector, the time projection chamber, and then the electromagnetic calorimeter. We should have completely finished dismantling by the beginning of September and most probably before then.'

At DELPHI, two thirds of the work has been done

Christian Joram, Technical Coordinator of Delphi and common activities in dismantling the four experiments:'We have been able to follow our schedule for the dismantling of DELPHI with a precision of a few days, and we should be finished by the end of May. 67 of the 80 planned tasks are completed, including the numerous subdetectors like the muon chambers or the internal detector. But the last tasks are the most colossal, with the lifting of endcap hadron calorimeters weighing some 900 tonnes. So far, everything has gone on very safely, with only one not very serious accident. Our only worry at the moment are the some 500 cubic metres of cables piled up on the four experimental sites pending permission from the Swiss customs to our contracted recycling company to import them into Switzerland. Otherwise, the cooperation between university institutes, CERN groups from various divisions and industrial firms has gone like a dream. At Delphi, the university groups have done a fantastic job. For example, in the space of only four weeks a team of four from the University of Padua in Italy completely dismantled the 128 modules containing 10 000 leadglass blocks in the endcap electromagnetic hadron calorimeters. A group from Oxford University in England dismantled more than 100 muon chambers. That kept them busy for a good month.'

L3 shared out across the world

Lucien Veillet, technical coordinator at L3: 'A third of the work has been done, but this represents only a tenth of the tonnage concerned. Within the central support pipe we have removed the entire machine portion, the hadron and electromagnetic calorimeters of the endcaps and the vertex detector. The lead glass bricks of the electromagnetic calorimeters have been shared out between the INFN in Rome and the French LAPP laboratory in Annecy. The vertex detector has been sent to the ETH in Zürich and the silicon vertex micro-detector to Perugia. The L3 cosmic experiment scintillator tiles on the external crown of the detector have left for China. Several muon endcap chambers have been recovered by the German Aachen institute and the Naples INFN, while sixteen others have been scrapped. Half the cables have been taken out. Incidentally, their removal is causing us a few headaches because lack of space in the underground halls means we cannot bring down large skips and the shaft gets easily clogged up. But generally, radiation measurements have shown it is more risky to spend a day skiing high in the mountains than down in the L3 cavern, the radiation readings are so low!'

OPAL stripped of its glass blocks

Alasdair Smith, technical coordinator at OPAL: "The dismantling of OPAL is near its half way point in terms of time. The 5 biggest counting rooms have been dismantled. On the detector side, the luminosity monitors and other detectors close to the beam pipe including the silicon microvertex detector were the first to be taken out, followed by the pole-tip hadron calorimeter, presampler and time-of-flight detectors and one half of the end muon detector. The entire central detector was extracted as a single unit, 4m in diameter and 5m long. The 2264 lead glass blocks of the 4 poletip lead glass arrays have now been removed. The next step is to move on to the barrel electromagnetic calorimeter which involves almost 10,000 lead glass blocks to be taken out in 10 pieces each containing about 1000 blocks! Work will also start on dismantling the central section of the magnet, consisting of a coil 4.5 metres in diameter and almost 8 metres long. Three other experiments are recovering cables for re-use. We are requested to clean the place out completely before the end of June, but that will be hard because it is the biggest pieces that still need to be dismantled.'