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Frequency Noise in Virgo

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.

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Frequency Noise in Virgo

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  1. Frequency Noise in Virgo by Matt Evans

  2. 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

  3. Sources: IMC Length Excitation • Injection bench alignment sensor noise below 15Hz • Seismic excitation • between 15 and 20Hz • also possibly higher… problem with suspension? • Actuator noise • IB coil-driver/DAC noise • Mode cleaner end mirror DAC noise

  4. Sources: Seismic Excitation

  5. Sources: IB transfer function • Dihedron resonace at 80Hz

  6. Sources: Actuator Noise • Dihedron resonace at 80Hz • Couples also through offsets (“FmodErr”)

  7. Frequency Servo MC path 100Hz Fast Loop 250kHz SSFS 25kHz

  8. Servo: Fast Loop • Noise properties not known

  9. Servo: SSFS

  10. Servo: SSFS

  11. Servo: MC path

  12. Coupling to the Dark Fringe • Line match at 444 and 1111Hz • Modulation spreads line power • The coupling fluctuates quickly • Coherent analysis is difficult • Noise projection is approximate

  13. Coupling to the Dark Fringe Line match Feature match B1 Shot Noise B5 Shot Noise ALL VERY ROUGH!!!

  14. Left to be Done • Tune SSFS • Increase gain between 1 and 5kHz • Improve phase margin by removing unnecessary delay in cables, OpAmps, ... • Understand fast loop noise • Electronics • Scattering on external bench • ND filters, clipping • Other ideas? • Stabilize coupling (alignment?)

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