LIGO Document P990007-v1

LIGO Beam Tube Module Design, Fabrication & Installation

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P - Publications
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27 Oct 2011, 04:46
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is designed to measure the gravitational waves emitted by astrophysical sources. Gravitational waves are ripples in the fabric of space and time caused by motions of objects in the universe. At the Earth, the ripples are sensed by measuring a small expansion of space in one direction and a contraction of space in an orthogonal direction. The observation is carried out by measuring the difference in the time it take laser light to travel along two orthogonal directions. The difference in the time compared to the average time, the gravitational strain, is expected to be 1 x 10-21 or smaller. The paths along which the laser beams travel are enclosed within 4 kilometer long, 1.2-meter diameter beam tubes. The tubes need to be under high vacuum and well aligned to reduce the disturbances from gas and wall scattering. This paper describes the configuration, fabrication and installation methodology used by Chicago Bridge and Iron Company (CB&I) to provide the beam tube modules for the LIGO facilities at Hanford, Washington and Livingston, Louisiana.
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Appended improved photographs provided 1 February 2019 by Marty Tellalian of CB&I to M. Zucker

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