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LIGO Hanford Observatory NewsStart Of HAM First Article Test Now In Progress!
The first article test of the seismic isolation system (SEI) for the Horizontal Access Module (HAM) chambers is in full swing at the LIGO Hanford Observatory. LIGO will use two types of large vacuum chambers to house optics and other interferometer components, the Beam Splitter Chambers and HAM chambers. Both accommodate sophisticated vibration isolation systems that attenuate by many orders of magnitude the transmission of ground motion to the locations where the optical components will be mounted. Corey Gray (BS Physics 1997, Humboldt State), who joined LIGO at Hanford in March, is assuming primary responsibility for the HAM SEI first article test, while Hugh Radkins (MS Geophysics 1990, Univ. of Utah), who joined LIGO at Hanford in May, is overseeing the first article testing of the BSC SEI. The BSC testing is going on in Los Alamos, New Mexico, at Hytec, Inc., the company that designed much of the SEI hardware.
These first article tests include both mechanical fit checks and system performance demonstrations (form, fit, and function). The HAM SEI testing is taking place in the lasers and vacuum equipment area (LVEA) along the Y-arm, past the output optics chambers for the four km interferometer. A view of the test area is shown in Figure 1. at left. The large structure with pink translucent curtains shown is a portable clean room enclosure. Inside the clean enclosure at left is a HAM chamber, and to the right is a wooden mock-up of a second ham chamber (lower vacuum shell only). Outside the enclosure to the right are two support tubes for the isolation system that have been prepared for insertion into the HAM chamber which requires passing them through the wooden mock-up. The blue cylindrical items in the foreground are the isolation system support piers.
C. Gray, H. Radkins, R. Savage, B. Miller from Hytec, and F. Asiri have been working over the past several months to perform fit checks and assemble the SEI support structure. Others from LIGO, including S. Whitcomb, D. Coyne, M. Barton, and H. Rong, have also been involved in the action at Hanford, and provided much-appreciated extra manpower. The hardware external to the HAM chamber has been located and secured in place; the support tubes, support table, and the bellows that provide the vacuum seal between the support tubes and the HAM chamber have been installed. The support tubes are in the process of being bolted to the crossbeams.Figure 2. at right is a view of the HAM chamber with the two large, 84"-diameter access doors removed. Visible in the center of the chamber is the seismic isolation system support table, which is bolted to the support tubes. The HAM chamber will not be evacuated during the first article tests, but the bellows are being installed for fit and vibration transmission tests.
Installation of the SEI stack, which consists of three layers of constrained-layer-damped coil springs and masses, is scheduled to begin presently. Performance testing of the isolation system is slated to start July 23 with M. Barton and A. Marin assuming primary responsibility. F. Asiri and M. Fine are coordinating fabrication of production components at commercial machine shops. Eight of the 12 HAM chambers at Hanford will be outfitted with seismic isolation systems similar to the one undergoing first article testing. Installation of those systems, beginning with the support piers, is scheduled to commence this August.