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Thermal noise resulting from ring dampers used for suppression of
parametric instabilities
Antonella Iuorio
University of Sannio, Benevento, Italy
LIGO Seminar
September 12, 2006
Eric D. BlackGrad students: Akira Villar, Greg Ogin
Surf student: Matt Seaberg, Cacey Stevens, Michael Goldman
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Acousto-Optic Coupling
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Instability Condition
Ju, et al. G050325-00 who got it from Braginsky, et al. Phys. Lett. A 305, 111 (2002)
Overlap factor
Stokes mode contribution
Anti-Stokes mode contribution
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Suppress parametric instabilities
How do we eliminate parametric
oscillations in AdLIGO without spoiling our low
thermal noise floor?
Active feedback
Thermal detuning
Ring dampers
Possible solutions
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Ring Damper
IDEA:To suppress the mechanical Q’s of many modes, without sensibly affecting thermal noise floor
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Previous results
• Rubber O-Rings
• Q’s decreased
• Broadband noise increased
• Kapton tape O-Rings
• Q’s unchanged
• Broadband noise unchanged
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Effect of dampers on Q’s
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Rubber O-Rings
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Kapton tape O-ring
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
No ring damperRubber O-RingKapton tape
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This summer’s results
Copper rings with screw
•Q’s decreased
• Broadband noise changed
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.QuickTime™ and a
TIFF (LZW) decompressorare needed to see this picture.
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What can we do?
Monolithic rings
Problem: Need to eliminate screw.
IDEA: Heat rings and cool in place
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Notch Filter
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Flavio Nocera
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Thermal Noise Interferometer
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Servo Block Diagram
Notch Filter
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TNI Total Noise
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Inductive heater for installing monolithic rings
• Induction coil induces an EMF in the ring damper
• Joule heating causes the ring to expand, so it will fit over the mirror
• Upon cooling, the ring shrinks to fit the barrel of the optic
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Schmitt trigger
• Comparator circuit with positive feedback
• The effect of the positive feedback is to make the circuit have two thresholds, depending on the output state
• Greater stability
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Summary
• Parametric instabilities
• Ring dampers
• previous results
• summer 2006 results
• My contribution
• Notch Filter
• Schmitt trigger
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Thanks
• Eric Black • Akira Villar
• Innocenzo Pinto • Greg Ogin
• Riccardo De Salvo • John Miller
• Vincenzo Galdi • Livia Cerullo