LIGO Document G1701304-v1

Search for Avalanches of Entangled Dislocations as a Source of Dissipation and Mechanical Noise

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Recent measurements have shown increased dissipation and the appearance of random low frequency instability in metal flexures. These effects have been attributed to entangled dislocations which, at a critical state, disentangle in avalanches that propagate through the material. This behavior is associated with the phenomenon known as Self Organized Criticality. These instabilities appear as deviations from Hooke’s Law and are observed as changes in the loss angle of the material. This experiment is a modern variation of the 1927 rotating cantilever rod experiment by Kimball and Lovell who discovered that the loss angle of a material is constant.

This research is attempting to induce avalanches of entangled dislocations to quantify the effects of these avalanches within metal flexures. The rotating cantilever beam attached to a material that will be put under strain from the effects of gravity. Due to the sag caused by gravity and the reactionary elasticity of the material, as the rod rotates dislocations in the crystalline structure of the material will propagate through the material. As these dislocations continue to collect, they will entangle and at a critical state, they will disentangle in avalanches that cause slight deviations from the equilibrium position of the end of the beam.

In this feasibility study, we have been able to demonstrate sufficient optical position resolution to accurately measure even small material loss angels and their fluctuations. A position resolution of better than 60 nm was demonstrated and a position resolution of 5 nm may be achievable with improvements. New breakthroughs in this feasibility study have been made to reduce outside noise. The next steps include the suspension of the experiment in a GAS filter and the implementation of a water-cooling system to keep the entire experiment at a stable temperature. With these improvements, the acquisition of data will begin.

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Amaldi 12 held on 09 Jul 2017 in Hilton Hotel, Pasadena, CA

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