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Investigation of mechanical losses of 3 rd generation gravitational wave detector materials

Investigation of mechanical losses of 3 rd generation gravitational wave detector materials Ch. Schwarz 1 , S. Kroker 2 , D. Heinert 1 , A. Tünnermann 2 , P. Seidel 1 1 Friedrich-Schiller-University Jena, Institute of Solid State Physics, Helmholtzweg 5, D-07743 Jena, Germany

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Investigation of mechanical losses of 3 rd generation gravitational wave detector materials

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  1. Investigation of mechanical losses of 3rd generation gravitational wave detector materials Ch. Schwarz1, S. Kroker2, D. Heinert1, A. Tünnermann2, P. Seidel1 1Friedrich-Schiller-University Jena, Institute of Solid State Physics, Helmholtzweg 5, D-07743 Jena, Germany 2Friedrich-Schiller-University Jena, Institute of Applied Physics, Albert-Einstein-Straße 15, D-07745 Jena, Germany DFG / SFB TR 7

  2. Aim for WP2: • Use of cryogenic techniques to reduce thermal noise • find and understand low mechanical loss materials for optics components • (thermo elastic damping & phonon-phonon interaction) • suspension materials and geometries with best available thermal • properties (e.g. conductivity) to reach required low temperatures and noise • budget

  3. Find and understand suitable materials for optics components • Available materials: • silicon • calcium fluoride • crystalline quartz • fused silica

  4. Most promising material: silicon - several publications about silicon (e.g. McGuigan et al.) show dips in the Q-factor around 120K and 18K > No measurements done in Jena showed dips at these temperatures

  5. Loss measurements of silicon cantilevers (as suspension elements in ET) in a frequency range between 25 Hz and 250 kHz The lowest mechanical loss measured was limited by TED between 50 K and 300 K

  6. Why is the knowledge about TED so important? - Depending on several parameters ( , , …) TED limits the mechanical losses between 100 and 18K > for a prediction of TED for a defined (ET mirror, suspension) geometry it’s necessary to solve the … thermal conductivity (2nd order tensor) Heat equation with deformation … thermal expansion coefficient The equation can be solved using COMSOL or ANSYS

  7. Anisotropic solution of the heat equation using COMSOL TED limits the mechanical Losses between 20 K and 120 K

  8. New design of the cantilevers for better handling Fragile cantilever covered by a “thick” frame of the same material

  9. Measurement of thermal conductivity - exact values for of available silicon samples for mechanical loss measurements - geometry dependence of for cryogenic suspension elements (e.g. silicon cantilever as plate spring)

  10. Future: - support of WP2 with experimental data of mechanical loss measurements and thermal conductivity - Further investigations of the phonon-phonon interactions at low temperatures using experimental data of thermal conductivity - calculation of TED for defined geometries

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