LIGO Document G0900127-v1
- All seismic isolation systems developed for Gravitational Waves Interferometric Detectors, such as LIGO VIRGO and TAMA, make use of Maraging steel blades. The dissipation properties of these blades have been studied at low frequencies, by using a Geometric Anti Spring (GAS) filter, which allowed the exploration of resonant frequencies below 100 mHz. At this frequency an anomalous transfer function was observed in GAS filter. Static hysteresis was observed as well.
These were the first of several motivation for this work.
The many unexpected effects observed and measured are explainable by the collective movement of dislocations inside the material, described with the statistic of the Self Organized Criticality (SOC). At low frequencies, below 200 mHz, the dissipation mechanism can temporarily subtract elasticity from the system, even leading to sudden collapse. While the Young’s modulus is weaker, excess dissipation is observed. At higher frequencies the applied stress is probably too fast to allow the full growth of dislocation avalanches, and less losses are observed, thus explaining the higher Q-factor in this frequency range. The domino effect that leads to the release of entangled dislocations allows the understanding of the random walk of the VIRGO and TAMA IPs, the anomalous GAS filter transfer function as well as the loss of predictability of the ringdown decay in the LIGO-SAS IPs. The processes observed imply a new noise mechanism at low frequency, much larger and in addition of thermal noise.
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