![]() ![]() To test the feasibility, the team decided to work directly above an 800-metre tunnel called TZ32. The necessary measurements will be made over a limited surface. "Our hope is to determine its shape to within a few microns," says Mark Jones, one of CERN’s surveyors, who is supervising the project. The shape of the geoid in this region is currently known sufficiently well to permit a relative precision of a few tenths of a millimetre for several hundred metres. In order to correct their instruments’ measurements for the effects caused by these gravitational anomalies, surveyors therefore need to determine the shape of the "geoid", which is a surface formed by all the points at which the gravitational potential energy is the same (corresponding to the value of the potential energy at mean sea level). But this is not the case rather, the field varies due to the uneven way in which masses are distributed at the surface of the Earth and below. The job would be straightforward if the gravitational field formed a perfect surface, e.g. ![]() It is therefore important to describe the gravitational field precisely within this purely mathematical system. Now, the accelerator design is defined in a system of Cartesian coordinates that is independent of gravity. ![]() The alignment systems currently envisaged for CLIC are no exception: long wires for horizontal positioning, and hydrostatic levelling sensors for vertical positioning. That affects in particular the ultra-precise optical levels and theodolites used for aligning accelerator components. One of the thorniest problems they have to face is that their measuring instruments are sensitive to the Earth’s gravity. That is the challenge facing CERN’s surveying section (part of the BE/ABP Group). CLIC needs 15 times greater alignment precision. Take the LHC for example: its components are aligned with a precision of approximately 0.15 mm over 100 m, which is already a remarkable achievement. This objective may sound a little bland, but in reality achieving such a level of precision will require incredibly complex technology. His goal: to show that the components of CLIC, the future electron-positron collider project, can be aligned with a precision of 10 microns (one-hundredth of a millimetre) over a distance of 200 metres. To this end, he has embarked on an unprecedented campaign of measurements, together with the CERN surveyors. The young man is in fact a PhD student in geodesy from ETH Zurich, doing research in the domain of ultra-precise measurements. He is neither an amateur astronomer, nor a contemporary artist looking for inspiration for an unusual work of art. On a beautiful summer’s night, Sébastien Guillaume sets up his camera equipment in the middle of the countryside and turns his lens towards the heavens, ready to spend a night photographing stars. Sébastien Guillaume during the zenith camera installation. To meet the alignment requirements for CLIC, the future linear accelerator project, CERN’s surveyors have started an unprecedented campaign of measurements. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |