Download - Noise Projections for GEO 600
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Noise Projections for GEO 600
Joshua Smith GEO Meeting
11.10.06
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Detector output decomposed
detector output:
detector output
noise source
transfer function
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Noise channels
noise channel
detector output:
detector output
noise source
transfer function
noise channels:
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Noise projections
noise channel
detector output:
detector output
noise source
transfer function
noise projections:
noise channels:
noise budget:
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Simplified procedure I
Causality key
Notes:
1. Causality key
2. Simultaneous DFTs allow comparison
3. Other variants exist, eg open-loop which requires CLTF
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Simplified procedure II
Causality key
Normal operation
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Simplified procedure III
Causality key
Normal operation
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Latest noise budget for S5
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Noise projection: alignment FB
transfer function
feedback
noise projection
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Noise projection: (de)modulation phase I
P
Q H
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Noise projection: (de)modulation phase II
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S5 NP ReconstructionGoal: Noise projections (full budget) at any time.
Coming soon: ProjMon
1. Transfer functions:
• Measure accurately about once per month
• Track using calibration lines
2. Fourier transforms of Nj and H:
• Signals recorded continuously anyway…
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Calibration lines
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Tracking transfer functions
•At calibration line, projection and H should have same amplitude, phase.
•Ratio and difference indicate TF accuracy.
•For 10 day test, about 10% 10o
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Vetoes of false gravitational waves
• Noise channels contain almost no GW info
• Coincident (within windows) events are not GWs !
•See Ajith and Martin’s talks !Example: injected burst-like waveform
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Noise subtraction: alignment FB
Results of a time-domain subtraction
Error at a given freq. vs. filter accuracy
H’
H
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The End
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Noise removal, eg., frequency noise
Most important role of NPs in commissioning: Identify limiting noise sources – team removes them
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Noise projection: laser frequency noise
Noise projections well-suited for very complicated systems
Transfer function calculation would require very sophisticated model
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Limitations: loop gain
Single-path loop
Workarounds exist:
eg., for high loop gain
Simulated results
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Limitations IISingle-path loop
Split-path loop
Workarounds exist: eg., for high loop gain
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H’ vs signal recycling FB
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Detector output I
detector output:
detector output
noise source
transfer function
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Detector output II
detector output:
detector output
noise source
transfer function