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Mirror Suspension Control VSR1 learning

Mirror Suspension Control VSR1 learning. E. Majorana INFN MSC workgroup. LSC-Virgo joint meeting Hannover 25-10-2007. outline. MSC status at VSR1 startup: quick reminder. MSC tuning during VSR1. Noise issues. Post-VSR1 considerations and perspective.

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Mirror Suspension Control VSR1 learning

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  1. Mirror Suspension ControlVSR1 learning E. Majorana INFN MSC workgroup LSC-Virgo joint meeting Hannover 25-10-2007

  2. outline MSC status at VSR1 startup: quick reminder. MSC tuning during VSR1. Noise issues. Post-VSR1 considerations and perspective.

  3. MSC status at VSR1 startup: quick reminder

  4. Mirror Suspension Control at VSR1 startup: essentials Compensation of actuator non-linear recoil: for both Marionette and SuperAttenuator. Global-Inverted-Pendulum-Control (partial): to increase Pos/Acc sensor crossover frequency (up to 70 mHz) without significant Seism re-injection (0.15-0.7 Hz). Pos/Acc prefiltering strategy tunable on-the-fly according to the wind (0.02-0.7) or sea (0.15-0.6) disturbance. Lock force hierarchically controlled through 4 marionette (two FP arms): to avoid saturations at low frequency. Local control roll-off (NI,WI,BSyaw) reduced to improve stability. IMC Suspensions (MC,IB) non-optimized and with no V-damp.

  5. MSC status at VSR1 startup: quick reminder (2-3). MSC tuning during VSR1

  6. MSC tuning and improvement during VSR1 • NI-WI LVDT/ACC : anti-Wind => anti-Sea => anti-Wind (Jun 5) • MARIO lock re-allocation on NI-WI OFF (NE,WE only) (Jun 6) • BS LC tuning to improve regions with small phase margin (Jul 4) • Seism-Free Reconstruction of PR top stage Err Signal (Jul 6) • EQG Guardian to disable GIPC in case of EarthQuake (Jul mid) • NI-WI mirror re-centring on beam (Jul mid) • GIPC and mSFR complete configuration (Sep 15) Overall Mirror Suspension Control Noise: no significant limitation of present Virgo sensitivity. Open issues: worse sensitivity during bad weather days (seism and wind).

  7. Initial Vs final: sensor prefiltering Example.. old old old new new new ACC HPw LPw mix cross IP HPs seism LPs LVDT + + mix =0 (wind-earthqukes, f <70mHz): “aggressive” attenuation of accelerometer tilt noise. mix =1 (seism, 150-600 mHz) : “aggressive”, slightly worsened against tilt noise. mix =0.5 ‘medium’ attenuation of LVDT seism noise Compared to the starting config (crossover @ 50 mHz). hybrid filters (on-the-fly tuning) HPLP mix VSR1: sensor prefiltering tuned, after few days, to reject wind diturbance injected by accelerometers.

  8. Initial Vs final: overall control strategies differential position deduced from GC reconstructed by local DSP Also the Acceleration ! seism coherent in the central area SFR possible by referring PR and BS to NI and WI seism incoherent along the arm baseline Seism reduced at END sites by using position referred to INPUT; misfunction during EQ WE GIPC PR NE BS GlobalControl INPUT TOWERS AS GROUND REFERENCE

  9. MSC Vs robustness (1): earhquakes/HNSNS drops/EQG patch Coherent excitation fast recover An automated Guard to disable GIPC: EQG zCorr Saturation Top-stage corr. from locking M6.5 GIPC cannot be used under coherent excitation (far EQ*) Mpc m m V V V 4-min to recover H instead of 30-40 min without EQG (*MSC talk at LSC-Virgo May07, plenary):

  10. MSC Vs rrobustness (2): earhquakes/stable GIPC MARIO: small residual correction (~7 m) Comparison of two events with similar local amplitude A “lucky” occurrence !* 40 m peak Previously we had saturation as the amplitude was less than 20 m The system is much more robust . Correction dynamics more than doubled. (*Indonesia M6.8, Sep-20-08.31):

  11. MSC Vs roboustness (3): earhquakes overall no unlock no unlock through GIPC disabling (EQG) unlock Local seismometric SA response Vs ITF lock m SFR_PR+EQG SFR_PRBS+stableGIPC day EQG action no longer needed. We use EQG as alarmed on-line seismometer

  12. Sub-conlcusion II higher cross-over (70 mHz) (lower wind noise without seism re-injection) & Coherent response to EQs Next ! ENV-TUNED GUARD Top-stage control strategies involving suspension operation as-a-whole improve disturbance rejection capability. EQ GUARD used in monitor mode. SFR (Central Area) GIPC (ARMs)

  13. MSC Vs seism (3) : main path/payload motion Effective attenuation of seism at the payload attenuation at the suspension point The lock force applied to the marionette corrects the residual payload motion, whose rms above 100 mHz is ~ 1 order of magnitude smaller than the ground motion.

  14. MSC Vs seism (4) : rejection VSR1start-VSR1stop quiet Monitoring of channels used for top-stage control at VSR1 start setup. Combined channels used at VSR1 stop: SFR (Seism-Free Reconstruction) and GIPC (Global-Inverted-Pendulum Control)

  15. MSC Vs seism (5) : rejection VSR1start-VSR1stop sea Monitoring of channels used for top-stage control at VSR1 start setup. Combined channels used at VSR1 stop: SFR (Seism-Free Reconstruction) and GIPC (Global-Inverted-Pendulum Control)

  16. MSC Vs seism (1): high seism day during VSR1 seism > 1.5 mrms Sensitivity stability seism < 1.5 mrms Sensitivity main misalignment indicators main stability indicators Horizon increase unaddressed noise bump seism decrease seism < 1 mrms: No effect Diff pitch at DF DF before OMC IBpitch OMC transmission Sideband pwr probe Carrier pwr probe

  17. Noise impact study using VSR1 data and sub-conlcusion III What is the coupling path ? Higher gain for injection bench angular control (pitch) necessary to improve stability during high sea activity. Even though the seism disturbance is the the range of suspension resonant frequencies, the overall impact at the level of the mirror is relatively small: a factor 10 of rms at the ground worsens by a factor 2 the accuracy of controlled signals at the ITF level.

  18. MSC status at VSR1 startup: quick reminder (2-3). MSC tuning during VSR1 (4-10). Noise issues).

  19. MSC status at VSR1 startup: quick reminder. MSC tuning during VSR1. Noise issues. Post-VSR1 considerations and perspective.

  20. OBO: attempts for systematics seism OBO multiple OBO multiple OBO Single NE_top WE_top NI_top WI_top BS_top PR_top IB_top MC_top OB_top ………. One-By-One injection to mimic seism disturbance occurred during VSR1 Probes Quiet Locking feedback on end mirror payload (zGC) Locking feedback on BS and PR (zCorr) End Mirror Alignment (B1p_q1_AC_pv) Input Mirror Alignment (B1p_DC) Injection beam jitter (IB_ty,IB_tz) ? Sideband power (B1_DC) …….. …….. …….. …….. 4 entry-points: END, INPUT,BS,PR,ISYS 3 d.o.f: longitudinal (z), transversal (x), vertical (y)

  21. OBO: injection at NE-WE top-stage, a “positive” clear result. activated probe END mirror pitch OBO SA TOP Payoad ITF GW channel Actual seism zGC pitch perturbed yaw unperturbed An efficient way to produce Horizon drops similar to actual one as seism rms is ~ 3 m is through mirror pitch noise (consistent with VSR1 experience).

  22. significant effect 200-300 Hz Injection @ NE-WE As expected, due to GIPC, injections @ NI-WI produce very similar effects.

  23. OBO: injection at IMC top-stages Very difficult to excite the IB simply injecting pseudo Seismic noise at the top-stage. Power fluctuations close to the actual ones only by using a strong line, tuned on IB main pitch mode.

  24. Injection @ InputMC no effect a surprisingly “negative” clinical result, Some hidden path…

  25. Sub-conlcusion IV and summary Two main effects ITF Power fluctuations Specific coupling with sensitivity due to diff.pitch Improvement of IB angular control (coming soon) • In order to cope with a noise bump at 200-300 Hz (that should be removed) we can: • decrease the gain demand to alignment • control (by setting input mirrors under AA) • - improve the strategy (higher LVDT/Acc • crossover and tuned reallocation techniques). Quite reasonably achievable to gain a factor 2 In spite of suspension resonances, normally there is no environmental seismic effect on the sensitivity. High seism means that the ground shake in the range 0.2-0.7 Hz can increase up to 10 times, worsening mirror control signals by a factor 2.

  26. Not used

  27. STANDARD CONFIGURATION FOR LONG SUSPENSIONS stage variable actuator ref SA TOP Pos/Accel 3D+yaw Ground(~)/stars SA BOTTOM Position yaw Ground PAYLOAD Position 2D+pitch/yaw SA BOTTOM Basic requirements: sensing and actuationdiagonalization + hiearchical control

  28. Virgo “standard-super-attenuator”suspension … • Soft isolator concept: • very efficient passive attenuation • active controls for normal mode damping

  29. seism Vs VSR1 sensitivity: quicklook to the data/seism > 1.5 mrms mSeism level: 3 m rms mSeism level: 2.5 m rms mSeism level: 2 m rms mSeism level: 1.5 m rms mSeism level: 1 m rms mSeism level: 0.5 m rms 100-500 Hz: power fluctuations due to injection misalignment driven + specific bump coupled to ITF pitch misalignments Other features: 10-100 Hz: glitches uncorrelated to power fluctuations 500-10000 Hz: small noise floor fluctuations well correlated to power fluctuations

  30. MSC Vs seism (2): main path/ground excitation LVDT sensor measures the position of top-stage suspension point (top of the IP) with respect to a grounded rigid mechanical frame. Top-stage LVDT channels provide the best measurement of ground noise

  31. MSC Vs seism (6) : residual impact Impact on the ITF longitudinal error signals

  32. MSC Vs seism (7) : residual impact Impact on the ITF angular error signals, in loop full bandwidth

  33. MSC Vs seism (8) : residual impact Impact on the ITF angular error signals, DC controlled in loop full bandwidth

  34. MSC Vs seism (9) : residual impact Impact on the IMC angular error signals, in loop longitudinal

  35. Injection @ BS small effect Not enough to explain the noise in actual condition, considering that the applied disturbance was much larger in OBO tests.

  36. Noise injection at BS suspension top-stage With a similar excitation of the top stage, the longitudinal accuracy is much worse. The angular motion is larger in tx, smaller in ty.

  37. Noise budget now + what next? (E. Tournefier) Control noises: further reduction - sensing/driving matrices improvements / 8 MHz? - angular control filters/ better signals with new end benches telescope Actuator noise is not far at low frequency => new coil driver (more filtering) Where is the Eddy current noise? Remaining mystery noise => Brewster removal + diffused light mitigation 700 Hz monster?? Cleaning of the mirrors + TCS will the error signals get cleaner?

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