PHARAO’s Cesium Tube
- Paper number
IAC-06-A2.1.04
- Author
Mr. Stephane Thomin, EADS-Sodern, France
- Coauthor
Mr. Christian Mace, EADS-Sodern, France
- Coauthor
Mr. Salem Belmana, EADS-Sodern, France
- Coauthor
Mr. Olivier Grosjean, Centre National d'Etudes Spatiales (CNES), France
- Year
2006
- Abstract
PHARAO (Projet d’Horloge Atomique à Refroidissement d’Atomes en Orbite), a scientific project funded by the Centre National d’Etudes Spatiales, together with a Hydrogen Maser, are two atomic clocks on board ESA’s ACES (Atomic Clock Ensemble in Space) platform which will dock on the International Space Station. PHARAO will be the first space atomic clock to use the physical principle of cooling of atoms, to make it the most accurate and precise clock ever built. EADS Sodern was selected to design, integrate and test two equipments of the clock, namely the Cesium Tube and the Laser Source, before final integration of the instrument by CNES in Toulouse. The other equipments of PHARAO are the microwave source and electronic units. The main challenges in the development of the Cesium Tube are simultaneous engineering, development of specific innovative technologies which are compatible with amagnetism and ultra-high vacuum and mass reduction. The Cesium Tube is mainly made of: - The Ultra-High Vacuum Tube where the Cs atoms are manipulated. The pressure in the tube must be maintained down to 1.5 x 10-10 mbar. Specific developments were needed in order to obtain this value : preparation of titanium surfaces, use of getters, development of a 3 l/s ion pump connected to a proprietary 5 kV power supply. - The magnetic subsystem is made of three concentric cylindrical magnetic shields and an original active compensation coil and servo-loop with a magnetometer in order to attenuate the outer Earth magnetic field by a factor of 400000. - The optical subsystem comprises 10 collimators fixed to the Ultra-High Vacuum tube and equipped with optical fibres for laser injection. Precise positioning of the laser beams is obtained by adjusting rotation and translation wedges on top of each collimator. The six degrees of freedom of each optical fibre may need to be adjusted independently on every collimator. The Engineering Model has been tested in Sodern and delivered to CNES in January and is now being tested in Toulouse. The paper mainly emphasizes some of the technological challenges encountered during the development of the Cesium Tube.
- Abstract document
- Manuscript document
IAC-06-A2.1.04.pdf (🔒 authorized access only).
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