Advanced LIGO two-stage twelve-axis vibration isolation and positioning platform. Part 2: Experimental investigation and tests results
This paper presents the results of the past seven years of experimental investigation and testing done on the two-stage twelve-axis vibration isolation platform for Advanced LIGO gravity waves observatories. This five-ton two-and-half-meter wide system supports more than a 1000 kg of very sensitive equipment. It provides positioning capability and seismic isolation in all directions of translation and rotation. To meet the very stringent requirements of Advanced LIGO, the system must provide more than three orders of magnitude of isolation over a very large bandwidth. It must bring the motion below 10^(−11) m/√Hz at 1 Hz and 10^(−12) m/√Hz at 10 Hz. A prototype of this system has been built in 2006. It has been extensively tested and analyzed during the following two years. This paper shows how the experimental results obtained with the prototype were used to engineer the final design. It highlights how the engineering solutions implemented not only improved the isolation performance but also greatly simplified the assembly, testing, and commissioning process. During the past two years, five units have been constructed, tested, installed and commissioned at each of the two LIGO observatories. Five other units are being built for an upcoming third observatory. The test results presented show that the system meets the motion requirements, and reach the sensor noise in the control bandwidth.
© 2014 Elsevier Inc. Available online 4 December 2014. The authors acknowledge and gratefully thank the National Society Foundation for their support. LIGO was constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the National Science Foundation, and operates under cooperative agreement PHY-0757058. Advanced LIGO was built under award PHY-0823459. We thank the JILA group for pioneering the work on active isolation systems using low frequency inertial sensors, and for demonstrating the feasibility of such multi-stage systems. We thank our colleagues from the suspension groups in GEO and LIGO for introducing us to the benefits of using triangular maraging steel blades to provide vertical isolation. We thank High Precision Devices for the mechanical design of the rapid prototype and the technical demonstrator. We thank Alliance Space Systems Incorporation for the mechanical design of the two-stage prototype. We thank Nanometrics, Streckeisen, Geotech, Sercel and Microsense for supplying us with great instruments, and for their technical support. Finally yet importantly, this work would not have been possible without the outstanding support of the LIGO laboratory management, computer and data systems, procurement, facility modification and preparation, assembly and installation teams. The content of the figures in Section 3.1 was adapted from figures presented in our ASME conference paper on "Dynamics enhancements of advanced LIGO multi-stage active vibration isolators" , with permission from the ASME. This document has been assigned LIGO Laboratory document number LIGO-P1200010. LIGO internal documents are accessible from the public document control center: https://dcc.ligo.org/cgibin/DocDB/DocumentDatabase.
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