Advanced LIGO subsystems
are the organizational units of the overall project. Follow the links below to view the mission and progress of each subsystem.
|Auxiliary Optics||Core Optics|
|Data Acquisition||Data and|
Advanced LIGO News
Large Optic Suspensions and Vibration Isolation Systems Enter the Vacuum
Multi-stage suspensions and noise-cancelling vibration isolation platforms represent two major thrusts of the Advanced LIGO program. Four-stage quadruple suspensions are the most complex of the aLIGO family of optic suspensions. These "quads" and the large optics that populate them will occupy the vacuum chambers that form the reflective boundaries of the four-kilometer arm cavities on each interferometer. Quad suspensions attach to the undersides of aLIGO vibration isolation platforms named ISI's (internal seismic isolation). The 3900kg ISI's can only enter LIGO's large vacuum chambers (BSC's) through the top of the chamber. Rather than lower the ISI into the BSC and then bring the quad through the side of the chamber for attachment, LIGO chooses to mate the quad to the ISI outside of the BSC. The photo above shows a quad/ISI assembly, known as a cartridge, resting on a test stand. Crews then then lower the entire wrapped cartridge into a BSC through the chamber top. LIGO has now accomplished two cartridge installations on the Hanford H1 detector.
The installation process must safely land the cartridge in the BSC while preserving the hardware alignments that assembly crews have taken great care to produce and verify. When inside the chamber, the large optic on the lowermost quad stage must rest within a millimeter of its position specification and within a milliradian of its angle specification. After the installation, LIGO's alignment specialists use precision surveying to assess the quality of the placement. The BSC ISI's consist of two suspended stages; this means that the large optics (also known as the test masses) are the terminal masses in a chain of six suspended stages. Alignment errors at any stage will take their toll on the final result.
Each of the several thousand suspension and ISI parts underwent cleaning and baking prior to inclusion in the assemblies. Cartridge installation must not degrade the clean state of the assemblies. HEPA-filtered air in LIGO's large instrument areas and portable clean rooms with additional filtering provide the main defense against particulate contamination. Shed-free custom-tailored fabric wraps protect the cartridge once the portable clean room moves aside to allow the craning to occur. All craning and rigging equipment must be free of contamination, including moisture and hydrocarbon contamination. The industrial scale of the cartridge installation creates challenges for the installation team at every step.
Now that LIGO Hanford has installed two cartridges at opposite ends of a single detector arm, the focus moves toward the single-arm test. Soon LIGO will send light from a green laser through the back of the mirror at the end of the arm. This light will need to strike the face of the inner cavity mirror four kilometers away, then resonate in the cavity during multiple reflections along the arm. LIGO's single-arm team will perform a variety of tests on the new Advanced LIGO hardware in both of these chambers to assess the performance of the suspensions, the vibration isolation systems and the control systems that regulate these components. The single-arm test represents a key intermediate stage on the path toward full interferometers.
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