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Frequency Noise in Virgo. by Matt Evans. The Actors. Noise Sources Input Mode Cleaner length noise Sensing noise on IMC lock Frequency Servo Servo topology Gain limitations Sensing noises Coupling to the Dark Fringe Common Mode Rejection Ratio Fluctuations. - PowerPoint PPT Presentation
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Frequency Noise in Virgoby Matt Evans
The ActorsNoise SourcesInput Mode Cleaner length noiseSensing noise on IMC lockFrequency ServoServo topologyGain limitationsSensing noisesCoupling to the Dark FringeCommon Mode Rejection RatioFluctuations
Sources: IMC Length ExcitationInjection bench alignment sensor noise below 15HzSeismic excitationbetween 15 and 20Hzalso possibly higher problem with suspension?Actuator noiseIB coil-driver/DAC noiseMode cleaner end mirror DAC noise
Sources: Seismic Excitation
Sources: IB transfer functionDihedron resonace at 80Hz
Sources: Actuator NoiseDihedron resonace at 80HzCouples also through offsets (FmodErr)
Frequency ServoFast Loop 250kHzSSFS 25kHzMC path100Hz
Servo: Fast LoopNoise properties not known
Servo: SSFS
Servo: SSFS
Servo: MC path
Coupling to the Dark FringeLine match at 444 and 1111HzModulation spreads line powerThe coupling fluctuates quickly Coherent analysis is difficultNoise projection is approximate
Coupling to the Dark FringeB1 Shot NoiseB5 Shot NoiseLine matchFeature matchALL VERY ROUGH!!!
Left to be DoneTune SSFSIncrease gain between 1 and 5kHzImprove phase margin by removing unnecessary delay in cables, OpAmps, ...Understand fast loop noiseElectronicsScattering on external benchND filters, clippingOther ideas?Stabilize coupling (alignment?)