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(Some) noise hunting issues at Virgo

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  1. (Some) noise hunting issues at Virgo Gabriele Vajente 11th ILIAS WP1 meeting Hannover, January 22-23 2007

  2. Summary • Searching for a good operating point • ITF sensitivity and longitudinal offsets • Alignment noise projections • Implementing HACR at Virgo

  3. Searching for the good operating point…

  4. Virgo scheme Beams B1 = dark fringeB2 = ITF reflectionB5 = BS pick-offB7 = north arm transmissionB8 = west arm transmissionScanning F-P on B1 DOFs DARM = differential long armsCARM = common long armsMICH = short michelsonPRCL = recycling cavity

  5. How to define a good O.P. • The ITF is at resonance, meaning powers are min/max at the locking point • In particular • Carrier resonates in PRC: B5_DC is maximum • Fringe is dark: B1_DC is minimum • Sidebands resonate in PRC: B5_2f_ACq is maximum • A consequence • Sidebands are well balanced at every port BS pick-off beam demodulated at 2W gives an estimate of sidebands power into PRC

  6. Evidence that MICH offsets was not good (November 10th) The old story But changing only MICH offsets is not enough to reach a good operating point DF power PRC power DF ratio PRC sidebands ITF reflection North transmission X axis = offset on MICH

  7. B2_3f_d1_ACp B5_d2_ACq The idea • MICH and PRCL loop are strongly related • Try to explore MICH-PRCL space by changing both offsets • Spiral experiment • Change simultaneously the two offsets • Error signals are reconstructed using Pr_B2_3f_ACp = ITF reflection demodulated at 3WPr_B5_ACq = BS pick-off demodulated • Add electronic offsets to these two signals • Need to wait 2 hours after lock to let the ITF “warm up”

  8. Spiral experiments • First “historical” one (November 24th 2006) • Proved the technique works • Second experiment centered around ”normal” locking point • Identified a new point, one night lock on it • Third experiment, centered around the new point

  9. First experiment Dark fringe ratio Sidebands inside PRC Sidebands imbalance at DF Power inside PRC OFFSET ON B5_ACq [ADC counts] OFFSET ON B2_3f_ACp [ADC counts]

  10. Conclusions of the first experiment • Moving to lower right corner: • Fringe is darker • B5_2f_ACq is higher • Sidebands are more balanced • But B5_DC is lower • Left the ITF locked all the night (from 23.00LT 28th to 8.00LT 29th) with new offsets • B2_3f_d1_ACp = 800 • B5_d2_ACq = -8000 Reached a bit more than 4 Mpc Never obtained with B2_3f

  11. Second experiment Second experiment (1100,-11000)

  12. Second experiment (1600,0)

  13. Second experiment

  14. Second experiment (1250, -6000)

  15. Conclusions of the second experiment • Three good candidates identified • Darkest fringe at (1100,-11000) • Maximum sidebands power in PRC at (1600,0) • Highest horizon at (1250, -6000) • The idea was to test all this points, measuring a sensitivity • But only the first one was briefly tested so far

  16. Improvements in sensitivity NSNS Horizon (opt) PRC power B2_3f offset B5 offset Loop UGFs Some lock signals DARM PRCL MICH

  17. Improvements in sensitivity Dark fringe Reconstructed h

  18. Conclusions on the operating point • The “normal” locking position is not the best operating point • Changing offsets it is possible to improve sensitivity quite a lot (horizon from 3 to 4.5 Mpc) • Still some tuning to do… • During WSR7 the ITF was run with an offset on B2_3f only • What to do next • Check repeatability (alignment issues?) • Offsets on CARM and DARM? • Find a new O.P. and tune parameters

  19. Alignment noise projections

  20. Measurements of alignment N.P. • Two methods: • Injection of noise (double zero @ 0 Hz, double pole @ 10 Hz, double pole @ 50 Hz) • Injection of lines13, 72, 119 Hz • Estimation of transfer functions and noise projection for dark fringe

  21. Some results / NE tx Coherence DF vs correction with noise Correction signal with and without noise Green stars are TF computed with the lines Trans. Func. Correction to DF with noise D.F. with and without noise

  22. Some results / NI tx Coherence DF vs correction with noise Correction signal with and without noise Green stars are TF computed with the lines Trans. Func. Correction to DF with noise D.F. with and without noise

  23. Some results / BS tx Coherence DF vs correction with noise Correction signal with and without noise Green stars are TF computed with the lines D.F. with and without noise Trans. Func. Correction to DF with noise

  24. Transfer function estimation with lines Coherence at lines (PR is not good) Trans. Func. at lines (PR is not good)

  25. Noise projection / tx (WSR7 sensitivity)

  26. Noise projections / ty (WSR7 sensitivity)

  27. Implementing HACR at Virgo

  28. Status • Started developing VirgoHACR • C code based on HACR algorithm • Full interface with Virgo Data Distribution via FdIO library • Output is a text file with events for the moment • Will be a MySQL database, to better interface with GEO report system • Very good performances • 1 s of data, 1 channel @ 20 kHz analyzed in about 10 ms of machine time • Limited by data access • Some test peformed

  29. Tests with simulated data… Map of short FFTs, white noise with bursts

  30. Tests with simulated data… All events are found, parameters are reconstructed well

  31. Test with simulated data… • Accuracy in time and frequency reconstruction

  32. Starting tests on dark fringe signal… Short FFTs map

  33. Starting tests on dark fringe signal… Mean FFT map

  34. Starting tests on dark fringe signal… Threshold crossing

  35. Conclusions on VirgoHACR • Code seems to work fine • Need some time to tune parameters for dark fringe • Still to do • Optimize parameter reconstruction • Output to database • Integration with GEO reports builder to create automatic reports