Session: Advanced Gravitational Wave Detectors and Advanced LIGO Technology (February 24, 2010)  

Title: UWA isolator control and integration

  Speaker: Pablo Barriga      

High performance vibration isolators are required for ground based gravitational wave detectors. To attain very high performance at low frequencies we have developed multi-stage isolators for the proposed AIGO detector in Australia. New concepts in vibration isolation including self damping, Euler springs, LaCoste springs, Roberts Linkages, and double pre-isolation require novel sensors and actuators. Double pre-isolation enables internal feedback to be used to suppress low frequency seismic noise. Multi-degree of freedom control systems are required to attain high performance. Two isolators suspending mirror test masses have been developed to form a 72 m optical cavity with finesse ~700 in order to test their performance. The suitability of the isolators for use in suspended optical cavities is demonstrated through their ease of locking, long term stability and low residual motion. I will describe the control components and control systems used to control all degrees of freedom. Feedback forces are injected at the pre-isolation stages and at the penultimate suspension stage. There is no direct actuation on test masses. A digital local control system hosted on a DSP (digital signal processor) maintains alignment and position, corrects drifts, and damps the low frequency linear and torsional modes without exciting the very high Q-factor test mass suspension. The control system maintains an optical cavity locked to a laser with a high duty cycle even in the absence of an auto-alignment system.

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