Stanford Program in Support of LIGO - Seismic Isolation and Controls

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In modern telescopes, much of the instrument's value lies in the stability of the mount and tracking. This is especially true for the Laser Interferometer Gravitational-wave Observatory (LIGO) - the value of the suspension and isolation is paramount because the mirrors must be suspended above the shaking ground. The work at Stanford is focused on the design and implementation of the mount that supports the optics for the 4-km long LIGO interferometer. The current facilities excel at isolating LIGO from the typical shaking of the ground; this grant will fund several related efforts to improve the robust operation of the LIGO detectors during large seismic disturbances, and it will also fund development of new techniques to isolate the optics of future, cryogenic detectors.To improve the duty cycle of the existing observatories, this grant supports work to mitigate the impact of wind storms on the detectors by combining computational fluid dynamics, wind tunnel tests, and observatory field measurements to develop low-cost wind barriers and improved control algorithms. The grant also supports development and testing of novel control schemes to help improve the operation of the detector during large, teleseismic earthquakes. Recent work has shown that nearly 90% of the low frequency ground motion during an earthquake is common to all the optics in the detector. The new research will actively coordinate the motion of all the platforms to simultaneously minimize the common-mode drives and the differential-mode motion over the 4-km length of the observatory. The large reduction in control force, and the improvement in differential excursions is expected to significantly improve the overall robustness of the detector. Stanford University operates the Engineering Test Facility, a 10-meter vacuum system with a prototype isolation system, where integrated hardware and software development for gravitational wave development is conducted. This grant funds research in this facility for seismic isolation of observatories which are now in the early planning stages. Future detectors are expected to use cooled optics to reduce the thermally driven (Brownian) noise of the mirrors. However, these mirrors will have more than a megawatt of laser power incident upon them, so running them at cryogenic temperatures requires the ability to continuous remove significant thermal energy. Techniques to do this will be tested on the prototype isolation platform so that the requirements for cooling and vibration control can be developed and tested simultaneously.