The vacuum system will be an extension of the existing 80m system consisting of maglev turbo pumps, scroll or diaphragm pumps for low capacity backing, and roots pumps for roughing. For reduced vibration, the main pumping facility will be moved to the 80m end stations, while ion pumps and titanium getter pumps will be mounted along the pipe and near to the central tanks as required. The vacuum pipes and suspension tanks will be made from specially pre-treated air-baked 304 grade stainless steel to reduce hydrogen outgassing. The spiral welded vacuum pipes will be made from 3mm 304L grade stainless steel. All material will be pre-air baked. The vacuum arms will be manufactured and cleaned on-site in 50 - 100m sections. To ensure mechanical stability against atmospheric pressure and thermal expansion, bellows will be located every 200m. Each bellows will have a 200mm elastic range and be supported by a stiffening ring to steel braces against a concrete footing. The pipe contains baffles to prevent light scattering. The pipe will be supported by concrete footings at 8m intervals. It will be located along the side of a 10m roadway. Concrete footings every 200m will be surveyed to ensure that the vacuum pipes are linear to within 5mm. This involves many subsystems, including the high power laser, the beam-forming optics, which consists of a frequency stabilising cavity, a premode cleaner and a 10m mode cleaner, and modulation optics for the control systems. At the end of this chain, a very precise and pure 100W laser beam is available for injection into the instrument. The picture above shows the mode cleaner tank and mechanical suspension assembly at the Gingin facility. From the mode cleaner onwards, the light must pass only through a vacuum to avoid acoustic disturbances to the beams and the mirrors. The rest of the optics system followsthe configuration shown on page 7. The next stage is the injection of the laser beam into the interferometer itself. This involves passing the beam through the power recycling mirror, the beam splitter and into the main interferometer arms. On this path it also has to pass through compensation plates that are used to correct the thermal distortions due to the small amount of light absorbed in the mirrors. After passing through the interferometer arms, where it builds up to about one megawatt of intensity, the light returns to the beam splitter and a tiny fraction of it approaches the output mirror. There are many alternatives to the design at this point, whereby different amounts of light can be recycled back into the detector. This final stage determines the instrument sensitivity at different frequencies, and is likely to be varied for different signal searches. The critical optical components for AIGO will be provided by CSIRO’S Australian Centre for Precision Optics. Control system software and some hardware will be supplied by international collaborators in conjunction with the UWA team. The Australian National University will create the output optics. The University of Adelaide will create the high-power laser and the monitoring systems for thermal lensing. The University of Western Australia will supply the suspension and isolation systems and carry out the supervision of the extension of the GPAC vacuum monitoring and control system supplied by Embedded Technologies. The vacuum pipes will by supplied by Duraduct together with CSIRO’s MIT Division, which will be responsible for the quality control, weld monitoring and inspection services.