1. GEO600 – The output mode cleaner Mirko Prijatelj for the GEO600-Team Institute for Gravitational Physics Albert-Einstein-Institute Hannover / Germany

2. Universe Outline The Output Mode Cleaner (OMC) Control system and control logic Stability problems

3. Universe DC-readout LIGO-G080405-00-L Controlled DFO

4. Universe Output mode cleaner Eliminates 99% junk light → Better sensitivity Finesse 150 Round-trip 65.8mm

5. Universe Output mode cleaner Junk light: Modulation sidebands & higher order modes Different resonance condition for carrier and junk light

6. Mode scan of GEO output GW-signal in transmitted power Need optimal transmission Control aspects: – Alignment – Length Static errors: Reduced sensitivity Dynamic errors: Noise sources Requirements derived from simulation: – Alignment: UGF << 1 Hz – Length: RMS reduction of ≈ 5 Control system requirements

7. Universe Control scheme Lock on OMC transmission peak Dithering – alignment @ 250-550Hz – OMC length @ 6kHz Error-signal at

8. New digital control system CDS = Control and Data System Similar to AdvLIGO Dithers & applies controls OMC  GEO interface via Labview Control setup CDS Control system

9. Universe Output mode cleaner Before OMC: After OMC:

10. Universe GEO stability during s6 Stable operation: GEO locks > 63h Reliable OMC lock acquisition (>> 90% success) Weeks without manual intervention

11. Universe Difficulty: Level 2 New seismic source Oct 17th 2010

12. Universe Difficulty: Level 2 Seismic increased up to a factor 10 Mostly < 10Hz Even at night!!

13. Universe Difficulty: Level 2

14. Universe Difficulty: Level 3 MSR exchange T=2% => T=10% Increased HOM

15. Universe OMC scan

16. Universe Lock acquisition Find transmission maxima in the right distances

17. Universe Control logic

18. Control setup Control infrastructure

19. Universe Control user interface

20. On switching / gain changes: Loop is nonlinear Switch ‚slowly‘ (3 steps, 3 sec apart) Hardware lowpass (2Hz) UGF ≈ 10Hz Control setup Length control

21. Switch ‚slowly‘ (3 steps, 3 sec apart) Control setup Length control

22. UGF ≈ 0.1Hz UGF below resonances in the loop => ‚Easy‘ shape Control setup Alignment control

23. Control setup Instability Instability after MSR change when locked to OMC power New MSR: – More HOMs leave IFO Gravel mining: – OMC alignment fluctuates more Combined effect: – More conversion from HOMs to TEM00

24. Universe Lets deal with it Seismic feed-forward for IFO mirrors => Reduce HOMs Faster OMC autoalignment => Less coupling of HOMs Advanced control loop design => More robust

25. Need to deal with pendulum resonances Rot: Pole 1.32Hz,Q=2.87 Tilt: Pole 0.78Hz,Q=2.28 Adapt servo design Control setup Faster OMC autoalignment

26. Compensate pendulum resonances in servo Control setup Faster OMC autoalignment

27. Beware actuator saturation Control setup Faster OMC autoalignment

28. Fluctuations are at low frequencies Use the aux diode for low frequency control Overall gain 120dB-> 130dB @DC OMC diode gain 120dB-> -6dB @DC No change at high frequencies Control setup Advanced control loop

29. Control setup Calibration fluctuations Get from [V/sqrt(Hz)] to strain [1/sqrt(Hz)] Introduce known length modulations (calibration lines) to calibrate signal DFO fluctuations => sidebands on calibration lines

30. Control setup Calibration fluctuations DFO spectrum 2.5,6,8Hz 2.5Hz: Pend. resonances 8Hz: Oscillating control loop

31. Control setup Calibration fluctuations Calibration line 305Hz DFO spectrum 2.5,6,8Hz

32. Universe Thank you