The ATLAS cavern in the spotlight
On Wednesday, 4th June, the President of the Swiss Confederation, Pascal Couchepin, inaugurated the world's largest experimental cavern, which is to house the ATLAS detector in 2007, and announced Switzerland's gift to CERN of the "Palais de l'Equilibre".
The inauguration ceremony was a spectacular affair. The President of the Swiss Confederation, Pascal Couchepin, arrived on the Meyrin site by helicopter and then made a 100-metre descent underground to inaugurate the ATLAS cavern. Before the ceremony, Pascal Couchepin attended a presentation of the various LHC experiments, each given by its respective spokesman. "It is a great pleasure for me to go behind the scenes of such a project and to see so many young people making a contribution to scientific progress" he said. The ceremony, which marked the end of five years of work on the ATLAS experimental area, was attended by many local politicians and Member State ambassadors.
A project of exceptional dimension
140 000 m3 of rock excavated, 53 000 m3 of concrete cast, 6 000 tonnes of reinforcement, 40 000 m2 of shuttering: just a few of the mind-boggling facts and figures that underline the scale of the work done by the CERN Civil Contractors joint venture (comprising Zschokke Locher SA, Baresel AG and PAT). These companies were responsible for the surface buildings, the two shafts, the service hall and, finally, the ATLAS cavern. A. Henninger, a representative of the joint venture, praised the performance of the approximately 100-strong team which worked a total of 400,000 hours, constantly exposed to hazards of various kinds.
The key component of the assembly is the experimental cavern, whose design and dimensions are unique. "Measuring 53 metres in length, 30 metres wide and 35 metres in height (the size of a ten-storey building), the excavation work undoubtedly constitutes a world record for this special type of mixed molasse rock found in the Leman Basin" underlined Luciano Maiani. Two large shafts measuring 18 and 13 metres in diameter, respectively, provide access to the cavern, which willultimately house the ATLAS detector. It is perpendicularly linked to a service hall measuring 65 metres long and 20 metres in diameter.
A civil engineering first
Even if they didn't have to move mountains, the civil engineers were neverthelessrequired to use a lot of ingenuity in order to excavate and concrete the experimental cavern without damaging LEP, which was still in operation and whose path cut right through it. Indeed, it was not possible to dig too deep without raising the height of the tunnel. The project managers were therefore required to be inventive and to depart from a few rules of the trade, including the order in which the work was performed. For example, the surface buildings were built in April 1998, before the two shafts started to be excavated, whereas excavation work is normally done before work on the surface. The advantage of this approach was that the buildings provided cover for the excavation work, thus cutting down on the associated environmental nuisance.
However, work on excavating the cavern had to start, irrespective of LEP operation, to avoid causing a delay in the schedule. It was decided to excavatethe top of the cavern to a depth of 12 metres, starting in May 2000, and to concrete the ceiling straight away. At this depth, the LEP beam was virtually unaffected. When the concreting was finished, a way of securing the 10,000 tonne ceiling to the rock had tobe found, a weight equivalent to that of the Eiffel Tower. The solution, adopted in August 2001, was to install thirty-eight steel cables, anchored in four small galleries 20 metres above, to suspend it. Each cable had to bear a weight of 220 tonnes, with the remaining load resting at the bottom of the walls of the shafts. The ceiling has not moved more than a few millimetres in the intervening two and a half years. Once this had been done, the excavation work was able to go ahead in September 2001.
The experimental cavern was completed on 15 April 2003 and handed over to the ATLAS collaboration. The last piece of concrete for the walls had been cast on 12 March. After some finishing work, mainly comprising renovation work on the surface buildings, the ATLAS experimental area will be completed on 20 June. The ATLAS collaboration will then take over for the installation of the detector.
The Palais de l'Equilibre becomes CERN's Globe of Innovation
In 2004, the elegant wooden dome of the Palais de l'Equilibre will dominate the entrance to CERN. During the inauguration of the ATLAS cavern, Pascal Couchepin announced that Switzerland would be giving CERN the famous building fromthe Expo.02 exhibition to mark the Organization's fiftieth anniversary. A gift of 4 million Swiss francs from the Swiss government will allow CERN to carry out the renovation work and begin to fit out the 27-metre-high globe. The gift is a mark of Switzerland'sesteem for the research conducted at CERN, says Pascal Couchepin.
The Palais de l'Equilibre is to become the Globe of Innovation, an approximately 1000 m2 exhibition area on two floors. It will promote CERN's research and its spin-offs for society. It will also be incorporated in the visits programme, which has been running for about twenty years and began with the Microcosm, which currently attracts around 30,000 visitors a year. The Globe of Innovation will also be a meeting place for CERN's partner companies, which will be able to take part in debates on the theme of emerging technologies.
