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GEO 600 Commissioning Progress at Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut)

This text discusses the progress of commissioning at GEO 600, focusing on improvements in signal recycling, calibration, and demodulation phase. It also highlights the challenges faced in the RF setup and noise reduction, as well as proposed solutions for future improvements.

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GEO 600 Commissioning Progress at Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut)

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  1. Title GEO 600 Commissioning progress Max-Planck-Institut für Gravitationsphysik(Albert-Einstein-Institut) Stefan Hild Ilias WG1 meeting, Sep 2005

  2. GEO 600 layout 0.09 1.5-2 kW

  3. Tuning signal recycling to 300 Hz • Better knowledge of IFO parameters: • more accurate prediction from simulations • downtuning to 200 Hz realized Fixed instability of MI auto-alignment by setting up a new telescope for DWS. We will stay at 330 Hz !

  4. GEO 600 design sensitivity

  5. Calibration and demod phase @ 300 Hz • Using signal recycling GW signal is split in P and Q quadrature P-response independant of demod phase Q-response only for larger than 20 to 30 deg demod phase compatible with current calibration (zero + complex pole) Decided to use 40 deg for time being. Drawback: ‚P‘ used for MI servo is not really only ‚P‘

  6. Q-comp OFF Q-comp ON High RF on HPD / Q-compensation • Observations: • Found huge RF level after MI diode (1 Volt) • Large DC level in Q after mixing. Q-compensation: Injected RF directly into resonance circuit of the HPD to make Q DC level zero. Improved sensitivity above 700 Hz

  7. NEW setup • New setup: • Using a less noisy splitter(0/90°) • Using a cable as phaseshifter RF setup OLD setup • Old setup: • Dominated by phase noise in the LO path (phaseshifter and splitter(0/90°) • Due to this noise from Q was mixed into P quadrature. • That is why Q-compensation worked.

  8. Shot noise Green line is the shot noise level calculated from the DC current of the photodiode. We are within a factor sqrt(2) shot noise limited above 1kHz !

  9. Future RF setup Proposed by Rana and others GOALS: • Using only high quality hardware • Guaranteeing high RF levels in all components

  10. Noise projections 21st of july

  11. Requirements • Large locking range • OLG of 10^6 at 0.1 Hz • No feedback noise above100 Hz Solutions • Servo has a locking mode and a running mode • Lowering UGF to get less gain in detection band • Using lowpass filter with very steep roll off above UGF (implemeted using a dSPACE system) Noise in the SR-long loop PROBLEM Noise in the detection band is entirely limited by front-end-noise (shot noise from the detector). Limits sensitivity from 100 to 500 Hz

  12. Analog SR electronics Red = acq amp, green = acq pha Dark blue = run amp, brown = run phase Light blue = run2 amp, pink = run2 pha

  13. Signal Recycling digital Phase @18 Hz = -147 deg

  14. SR feedback: analog vs. digital

  15. SR loop filter future design Four complex integrators: 2.25 (2x),1.3, 0.56 Hz Filter not used at the moment. Can be implemented when more gain is needed around pendulum resonances

  16. Sensitivity improvement July to August High frequency improvements: reduction of RF phase noise Low frequency improvements: reduction of Signal recycling feedback noise

  17. PR-bench Historically grown layout of PR-bench not optimal ! • beam clipping • too many transmissive optical components • too many polarizing components • acoustic coupling Goal: Shorten and simplify the HPD path

  18. Sensitivity after PR bench work Removed resonance structures between 100 and 200 Hz.

  19. Noise projections 21st of july

  20. < 0.1Hz Michelson length control

  21. Michelson length control < 0.1Hz < 10 Hz • Reaction Pendulum: • 3 coil-magnet actuators at intermediate mass, range ~ 100µm

  22. Michelson length control < 0.1Hz < 10 Hz • Reaction Pendulum: • 3 coil-magnet actuators at intermediate mass, range ~ 100µm • Electrostatic actuation on test mass bias 630V, range 0-900V= 3.5µm > 10 Hz

  23. Noise is introduced: • loop electronics • sqrt circuits • intrinsic HV amplifier noise Using ESD as actuator • Force is proportional to square of applied voltage. • high voltages are needed • for bipolar acting a bias voltage needs to be applied

  24. Sqrt circuits in MI loop ESD: F  U^2 Sqrt circuits are necessary to give full linear force range for acquisition. Drawback: sqrt circuits are noisy 1µV/sqrt(Hz) (=100µV/sqrt(Hz) @ ESD)

  25. Sqrt circuits in MI loop ESD: F  U^2 Sqrt circuits are necessary to give full linear force range for acquisition. Drawback: sqrt circuits are noisy 1µV/sqrt(Hz) (=100µV/sqrt(Hz) @ ESD) Bypassing sqrt circuits after lock is acquired.

  26. Noise in MI loop HVA noise = 100nV/sqrt(Hz) (=10µV/sqrt(Hz) @ ESD) HV-amplifier noise can be reduced by decreasing bias voltage or active noise suppression. Suppressing noise introduced by loop electronics needs whitening

  27. dewhiten dewhiten dewhiten Whiten MI loop whitening / dewhitening Whitening right after mixer: zero 3.5 Hz pole 35 Hz Dewhitening for both split passes Passive dewhit-ening done in HV path (0-1kV)

  28. Sensitivity after fixing noise from MI loop

  29. Michelson servo design

  30. MI loop gain problem • Strange observations: • We are not able to increase the low frequency loop gain, even though it should work from loop model (oscillation around 8 Hz) • OLG measurements show that there is nearly no gain around 8 to 10 Hz. • We needed to turn down the MI crossover gain continiously for the last few months • Findings: • Influence of MI AA gain on maximum cross over frequency (AA-tilt ,  cross over possible. •  phase margin of crossover, can  crossover frequency, but adding integrator still causes 8Hz oscillation •  IM gain ( crossover frequency),  less noise in servo 4 to 8 Hz. •  IM gain, still low gain around 8 to 10 Hz (low gain can‘t be caused by IM)

  31. Injecting LF noise in MI loop Injected noise from 5 to 11 Hz Between 6 and 7 Hz the noise is not suppressed !

  32. Measurement of open loop gain (PRMI) • Resonance structure • is clearly visible • Very low gain • around 9 Hz • Design gain: • 7 @ 15 Hz • 20 @ 10 Hz • 80 @ 6 Hz

  33. Mi servo design detail

  34. TF: Alignment to longitudinal Tilt couples a factor of 10 stronger than rot @ 10 Hz. (IM-FF tilt2long) Why are the two rot-TF so different?

  35. How to go on with the MI loop gain problem Measure MI loop gain for various conditions to decouple crossover and AA-tilt. Implementing digital AA control to be more flexible (nearly done). Measure tilt2long for single suspensions, with the goal of setting up a FF system. Investigate possible advantages of using the ESDs for angular alignment. ....

  36. Segmented ESD for alignment

  37. Sensitivity improvement of GEO

  38. Latest noise projections

  39. Current sensitivity vs. Design sensitivity

  40. Discussion • Michelson loop gain problem: • What experience exists in VIRGO with angular to longitudinal and longitudinal to angular couplings ? • Is somewhere gain lost ? • ... • Digital filtering: • What kind of filters are used within VIRGO for steep roll off?

  41. E n d

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