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Virgo central interferometer: commissioning and engineering runs

Virgo central interferometer: commissioning and engineering runs. Matteo Barsuglia Laboratoire de l’Accelerateur Lineaire, Orsay. Summary. Introduction The central interferometer Operation with a simple Michelson Operation with a recycled Michelson

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Virgo central interferometer: commissioning and engineering runs

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  1. Virgo central interferometer:commissioning and engineering runs Matteo Barsuglia Laboratoire de l’Accelerateur Lineaire, Orsay

  2. Summary • Introduction • The central interferometer • Operation with a simple Michelson • Operation with a recycled Michelson • Operation with the full injection system • E-run programs • Conclusions

  3. Virgo aerial view Pisa

  4. Virgo sensitivity Seismic noise Shot noise Thermal noise

  5. Virgo optical scheme

  6. The central interferometer (CITF) BS

  7. CITF: goals • Test all the tehcnical choice during arm construction: • Suspensions • Fully digital control chain • Output mode-cleaner • Local controls

  8. Suspensions Top stage Last stage Seismic filters

  9. Suspension Control Top stage • Lower suspension stages: • “marionetta” (from upper suspension stage) • mirror (from “reference mass”)

  10. Control Architecture • For each suspension • DSP • correction sharing • Resonance compensation • local controls • DAC 20 bits • Completely digital • LinxOS • C or C++ • photodiode-read-out 20 kHz • Control 10 kHz GPS Timing DOL’s • Photodiodes (powerPC platform): • ADC 16 bits • compression dynamics filters DOL’s • Global control (PowerPC platform): • read phd signals • algorithm for lock acquisition • linear locking and alignment

  11. Local Controls Output mode-cleaner • Completely out of vacuum • CCD camera • Coarse system, markers (50 mrad) • Fine system (laser beam, optical lever) • Control from marionetta (noise filtering)

  12. Detection system Suspended detection bench Output mode-cleaner

  13. Operation with a simple Michelson • Superattenuator controllability • Hierarchical control • Digital control chain • Output mode-cleaner • Control robustness

  14. Suspension performances • No excitation of unwanted degrees of freedom • High robustness to non stationnary noises • Passive filtering experiment (see Braccini’s talk)

  15. Force applied to mirror No feedback to top stage 3.5 mN with feedback to top stage Michelson locking with top stage Slow corrections (f < 70 mHz) Fast corrections (f > 70 mHz)

  16. Control robustness • Results from E0 run (72 hours) : ITF continuouslylocked on • dark fringe for more than 51h • 1 unexpected loss of locking, duty cycle > 0.98 % unlocked (bright fringe) 51 hours locked (dark fringe)

  17. OMC locking on dark fringe Transmitted power TEM00 TEM00 TEM00 TEM00 c2 signal Contrast improvement ~ 10

  18. Operation with a recycled Michelson • Lock acquisition • Frequency stabilization • Linear alignment

  19. Lock acquisition

  20. The lock acquisition problem North tunnel • Force needed to stop the mirror (finesse = 250) • maximum force 40 mN (limited by EM noise) modules storage

  21. Strategy (I) - enlarge the acting time North tunnel • Widening the error signal Pr_B5_ACq p (Pr_B5_DC) • Use of an antisymetric trigger few % close > 50 % open modules storage

  22. A simulated lock acquisition recycling speed Dark fringe speed trigger WI correction ITF internal power PR correction

  23. A real lock acquisition ITF internal power Dark fringe power Correction PR Correction WI

  24. Frequency stabilization • crossover ~ 3 Hz • very aggressive filtering above 13 Hz

  25. Linear alignment

  26. Linear alignment - results ugf ~ 5-10 Hz

  27. Operation with injection system

  28. Acquisition detection switch • Dark fringe control switched from B1p to B1 • Offset between B1p and B1 • dark fringe on B1p  dark fringe on B1 • Need offset compensation and smooth transition

  29. Optical characterization • Input power ~ 2 - 2.5 Watts • Recycled power (maximum) ~ 240 Watts • Not coupled light ~ 30 % • Interferometer contrast: • ~ 5 10-4 (before OMC) , • ~ 5 10-5 (after OMC)

  30. Alignment control noise Laser frequency noise E4 sensitivity

  31. High frequency noise Peaks: mirrors + holders Laser frequency noise

  32. Intermediate range noise • mode-cleaner mass TF • no common mode loop

  33. CITF e-run program • 5 e-runs (september 2001-july 2002) • 72 hours each • 8 hours shift • 4 people in shift (1 ITF, 1 laser/injection, DAQ, 1 learner) • 12 on call sub-system experts • central building closed, remote control

  34. Sensitivity evolution during e-runs

  35. Lock robustness during e-runs Run #losses (in ‘normal’ operation) duty cycle longest lock E0 1 (local ctrl fail) 98% ~ 51 h E1 1 (local ctrl fail) 85%~ 27 h E2 3 (2 ctrl software, 1 vacuum) 98%~ 41 h E3 4 (1 ctrl software, 3 ctrl tuning) 98%~ 40 h E4 4 (2 ctrl software, 2 injection) 73% ~ 14 h Normal operation = no experiments, no special conditions, no calibration

  36. Data acquisition during e-runs • 20 kHz • 2 writing processes in paralles • ~ 4 Mbytes/sec • 1 Tbyes/e-run • 3 kind of data streams: • 20 kHz frames • 50 Hz • Trend (1 Hz)

  37. Run overview – E4 (July 2002) calibration and other special investigations ~ 7 hours calibration ~ 3 h 30’ « stable » operation ~ 61 h 30’

  38. Duty Cycle – E4 • Normal operation ~ 61h 30’ • Locked ~ 42h 20’ •  Duty cycle ~ 73 % • 6 streams with CITF locked • longest (5) ~ 14h 30’ • shortest (3) ~ 55’ 4 6 2 1 3 5 Duty cycle limited by lock acquisition problems of retroreflected light from ITF to injection system

  39. Investigation groups • Sources of lock losses • Suspension motions • Angular drifts • Output mode-cleaner • Calibration • Angular noise • Seismic noise • Acoustic noise • Noise gaussianity/stationarity • Glitches • Lines identification • Injection system noise

  40. Lock losses study - example 1 sec • burst in the local controls of IB

  41. Locking accuracy Offset = 4 ·10 -14 Rms = 1 ·10 -12 Offset = 1 ·10 -11 Rms = 9 ·10 -12

  42. Conclusions - sensitivity • Solutions for frequency noise • Replace MC suspension • Add “common mode” loop • Solution for alignment noise • automatic alignment • filtering of high frequency noise

  43. Conclusions - I • Technical choices validated • superattenuators • “out of vacuum” local controls with CCD cameras • digital control chain • output mode-cleaner and detection system • Lot of experience • E-runs program very useful for detetector characterisation

  44. Virgo Planning • Now: • large mirror installation • vacuum leak tests • new MC suspension • local control improvements

  45. Mirror installation I

  46. Mirror installation II

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