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Matters of Gravity
LIGO Update for Spring 1995

by Stan Whitcomb

     The Laser Interferometer Gravitational-wave Observatory (LIGO) project was given a major boost in November when the National Science Board met to consider LIGO and approved the new project plans. This approval included a revised construction estimate and subsequent funds for the commissioning and initial operations. The strong backing of the National Science Foundation director and staff and the strengthening of the project management were key elements in gaining the support of the National Science Board.

     The pace of work on the Project has increased substantially over the past six months. Site preparation is well underway at the Washington LIGO site and should begin soon at the Louisiana site. The rough grading (the earthwork to level the foundation plane) has been completed in Washington and the site will be allowed to settle while the design of the foundations is finalized. The site in Louisiana has been purchased by Louisiana State Unviersity and leased to the NSF for LIGO. The Environmental Assessment has been completed; clearing of the site will begin as soon as the final environmental approval is given.

     A test of the beam tube design is now underway. This is a test of the design developed by our contractor (Chicago Bridge and Iron). It involves a full diameter section of beam tube approximately 40 m long, fabricated with the techniques planned for the LIGO field installation. The key aspects of the design to be tested are the leak-tightness of the welds and the outgassing of the fabricated tube. The tube is now under vacuum and a bake-out of the tube (140 C for 30 days) is planned to start in early February.

     The Ralph M. Parsons Company was selected as the Achitect-Engineer for the LIGO facilities. They will design the building for the two LIGO sites, including the foundations and covers for the beam tubes. They will also take responsibility for the site planning and eventually provide management oversight for the actual construction. Parsons was selected after a nationwide solicitation and a very rigorous competition.

     The final major facilities design contract is for the vacuum system, including the chambers, pumping system, and vacuum instrumentation, but excluding the beam tubes. Proposals for this contract are due in February and we hope to have the design work underway before summer.

     The major highlight from the R&D program is another improvement in the sensitivity of the LIGO 40 m interferometer. New test masses were installed in the interferometer. These new test masses are of a monolithic design with the mirror surface an integral part of the test mass; the earlier test masses had a compound construction with mirrors optically contacted onto a fused silica body. The compound design appears to have been a source of noise. The interferometer now has a peak sensitivity (near 450 Hz) of 2.5 x 10-19 m/Hz1/2, expressed as an equivalent differential arm length.

     The LIGO Project is now operating a World Wide Web server which will provide access to general information about LIGO, latest news and results, preprints and technical reports, and other relevant information. You can access our home page (our URL is "http://www.ligo.caltech.edu/") using Mosaic or another WWW browser. We expect that this will become one of the principal channels of communication with the interested scientific community.

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Last modified May 13, 1995