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Status of VIRGO

Status of VIRGO. Lisa Barsotti - University and INFN Pisa – on behalf of the Virgo Collaboration. Locking of Full Virgo. ILIAS. CASCINA - January 24 th , 2005. WI. PR. BS. NI. 3-km Fabry Perot cavities in the arms.

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Status of VIRGO

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  1. Status of VIRGO Lisa Barsotti- University and INFN Pisa – on behalf of the Virgo Collaboration • Locking of Full Virgo ILIAS CASCINA - January 24th, 2005

  2. WI PR BS NI 3-km Fabry Perot cavities in the arms VIRGO Optical Scheme

  3. Commissioning Plan Steps of increasing complexity: Sept 2003 – Feb 2004 • A SINGLE FABRY-PEROT CAVITY PR misaligned North Cavity

  4. Commissioning Plan Steps of increasing complexity: Sept 2003 – Feb 2004 • A SINGLE FABRY-PEROT CAVITY • Check of the performances of the sub-systems • Check of the control systems in a simple configuration West Cavity PR misaligned

  5. Commissioning Plan Steps of increasing complexity: Feb 2004 – Dec 2004 • A FABRY-PEROT MICHELSON ITF “RECOMBINED” MODE West Cavity • Intermediate step towards full Virgo • Start of noise analysis PR misaligned North Cavity

  6. Commissioning Plan Steps of increasing complexity: Since Sept 2004 • A POWER RECYCLED MICHELSON ITF West Cavity “RECYCLED” MODE • Final configuration PR aligned North Cavity

  7. Transmitted Power WE WE WI WI PR PR NI NI NE NE BS BS Demodulated osymmetric beam Control Scheme Commissioning of a Single Fabry-Perot Cavity - I Lock at the first trial 28th Oct 2003 Power Fluctuations laser freq noise & mirror angular motion T=8%

  8. Transmitted Power Commissioning of a Single Fabry-Perot Cavity - II Three Commissioning runs in a single cavity configuration: • C1 (14-17/11/2003)- North cavity and OMC locked IMC control noise reduced • C2 (20-23/02/2004) • - C1 + Automatic alignment • - West arm locked • C3 (23-27/04/2004) • - C2 + Laser freq stabilization

  9. Commissioning of a Single Fabry-Perot Cavity – III • Sensitivity Progress Three Commissioning runs in a single cavity configuration: • C1 (14-17/11/2003)- North cavity and OMC locked C1 IMC control noise reduced C2 C3 • C2 (20-23/02/2004) • - C1 + Automatic alignment • - West arm locked • C3 (23-27/04/2004) • - C2 + Laser freq stabilization

  10. Commissioning of the Recombined ITF WE WI PR NI NI NE NE BS BS

  11. Sensitivity ~ ~ 1 W 10 W P0 PBS Commissioning of the Recombined ITF PBSexpected in recycled mode ~ 500 W WE Start of some noise characterization WI ( 500 W) PR NI NI NE NE BS BS

  12. Recombined ITF Optical Scheme 8 West Transmitted beam WE WE WI WI PR PR NI NI NE NE BS 7 North Transmitted beam T=8% 5 Pick-off beam 2 Reflected beam 1 Asymmetric beam

  13. L2 l2 l1 L1 Recombined ITF Optical Scheme 8 • 3 d.o.f. ‘ s to be controlled: • Lengths of the kilometric arms:L1 and L2 • Michelson asymmetric length:l1 – l2 • fields not mixed WE WE West Cavity Simple Michelson WI WI North Cavity PR PR NI NI NE NE BS 7 T=8% 5 2 1

  14. 2_quad 1_demod Recombined ITF –Lock Acquisition 8_demod • Lock of the two arms indipendently with the end photodiodesCorrections sent to NE and WE • Lock of the michelson with the asymmetric port signal Corrections sent to BS West arm North arm 7_demod Michelson length

  15. Recombined ITF - Linear Locking • End photodiodes very usuful for lock acquisition but too noisy • Cavities controlledwith the reflected and the asymmetric beams West arm Michelson North arm 2_quad 2_phase 1_demod Differential mode of the cavities Common mode of the cavities

  16. Commissioning Run C4- June 2004 • Recombined Data Taking Mode • ITF controlled with the reflected and the asymmetric beams • Automatic alignment of the cavities • Laser frequency stabilized to cavities common mode • Cavities common mode locked to reference cavity • Output Mode Cleaner locked on the dark fringe • Tidal control on both arms

  17. Commissioning Run C4- June 2004 • 5 days of run • Longest lock ~ 28 h • Lock losses understood • h reconstruction on line

  18. Michelson controller signal C4 After frequency modulation tuning Commissioning Run C4: Noise Characterization Coupling of IB resonances into the michelson controller signal due to a mismatch between modulation frequency and input mode-cleaner length see Flaminio’ s talk

  19. After C4 • July – August • Upgrade of the terminal benches -> Re-tuning and improvement of the linear automatic alignment • Suspension full hierarchical control started • Commissioning of the Recycled ITF started • Effect of the backscattered light in the IMC -> attenuator installed between the IMC and the ITF • Mid September: Re-Start • October – November: -> Recombined ITF locked with the full hierarchical control of the end suspensions -> ITF locked in recycled mode

  20. marionette reference mass 103 y mirror z x z Suspension Hierarchical Control • Locking acquired and maintained acting at the level of the mirror • Reduce the strength of the mirror actuators by a few 103 to reach Virgo design sensitivity

  21. Corrections sent to the marionette TIDAL CONTROL DC-0.01 Hz Corrections sent to the mirror 0.01-8 Hz RE-ALLOCATION OF THE FORCE Force on the mirror reduced of a factor 20 • Switch to low noise coil drivers 8-50 Hz Suspension Hierarchical Control

  22. Suspension Hierarchical Control • SUMMARY • Single arm locked with the hierarchical control for the first time in July -> controllability of the superattenuator demonstrated • Last main result: hierarchical control of the recombined ITF in the C4 configuration, with automatic alignment and frequency servo engaged • Stable lock -> tested in the last commissioning run (C5, 2-6 December 2004)

  23. Lock Acquisition of full VIRGO • Chronology • Simulations on a lock acquisition technique developed following the LIGO experience • Locking trials with this baseline technique (first half of July) • Attenuator installed (summer) • Restart of the locking trials with the baseline technique (21st September) • Debugging of the sub-systems • Establishement of theVariable Finesse lock acquisition technique (October)

  24. Recycled ITF:Base and Photodiodes West Transmetted beam 4 lengths to be controlled: 8 • MICH = ln-lw • PRCL= lrec+(lN+ lw)/2 • CARM= LN+LW • DARM= LN-LW WE WE LW WI WI lW PR PR NI NI NE NE BS BS lrec lN LN 7 North Transmetted beam 2 5 1 Reflected beam Asymmetric beam

  25. Baseline Technique • Based on the LIGO technique • Multi–states approach • Dynamical inversion of the sensing matrix

  26. Experimental Activity:Lock of Stable States - I • Sidebands locked in the recycling cavity Reflected f-demod signals to control MICH and PRCL STABLE STATE 2 2_phase 2_quad

  27. Experimental Activity:Lock of Stable States – II • Sidebands locked in the recycling cavity, carrier locked in the FP Reflected f-demod signals to control MICH and PRCL STABLE STATE 3 2_phase 2_quad

  28. From f-demod to 3f–demod signal • CARM contamination in the PRCL reconstruction State 4 Simulated Sensing Matrix • Frequency Response of the f-demod signal very sensitive to the ITF losses

  29. PRCL Frequency Response - I Input FP Mirrors Losses 1%o • SIMULATION B2_f_phase Non - Minimum Phase

  30. PRCL Frequency Response - II Input FP Mirrors Losses 1%o • SIMULATION B2_3f_phase Minimum Phase

  31. 3f - Demod Signals VIRGO Lock Acquisition Scheme • Good decoupling MICH / PRCL • Less CARM contamination in the PRCL signal • Almost Diagonal Sensing Matrix REF BEAM phase 5_phase REF BEAM quad 1_phase

  32. BS – PR Corrections NORTHandWESTPower Recycling Cavity Power NE – WE Corrections First Locking Trials

  33. MARCH OCTOBER Drawbacks of the Baseline Technique: PR Transfer Function • PR transfer function The lock acquisition technique is “statistical”.  transients, ringing Compensation of the PR Resonances: critical, high Q

  34. Drawbacks of the Baseline Technique:the CARM contamination • The optical design of the ITF makes the response of the reflected 2_f signal very depending by the losses Use of the 2_3f signal in the lock acquisition phase • The CARM contamination is anyway critical : • use of SSFS is possible only in a steady state regime

  35. A new strategy:theVariable Finesse Lock Acquisition

  36. The Variable Finesse Locking Strategy “A recycled ITF with a low recycling factor is similar to a recombined ITF “ • End photodiodes • Lock immediately the 4 degrees of freedom of the ITF on the half/white fringe (low recycling factor) • lock of PR prevents ringing and transient effects • lock of the cavities prevents CARM contamination • Bring the interferometer adiabatically from the half to the dark fringe increasing the recycling factor

  37. WE WI PR NI NE BS Half Fringe The Variable Finesse Locking Strategy • Lock immediately the 4 degrees of freedom of the ITF on the half fringe: • end photodiodes to acquire the lock of the long cavities Low Recycling Factor • simple michelson locked on the half fringe with the asymmetric DC signal • 3f demodulated reflected signal to control the recycling cavity length

  38. The Variable Finesse Locking Strategy End photodiodes start to see both the cavities: We can not continue to control the arms indipendently

  39. The Variable Finesse Locking Strategy • Laser frequency stabilization engaged • One of the end photodiodes used to control the differential mode of the cavities WE • Laser stabilized on the common mode of the cavities Low Recycling Factor • PR realigned WI • Offset in the mich DC error signal reduced approaching the dark fringe PR NI NE BS Half Fringe

  40. LASER The Variable Finesse Locking Strategy WEST TRANSM BEAM • From the DC to a demod signal to control the michelson length 2_3f_ph 5_ph 5_q

  41. The Variable Finesse Locking Strategy • Final Step : To the Dark Fringe ITF on the operating point

  42. LASER The Variable Finesse Locking Strategy RUNNING MODE: Switch to the main GW signal to control the DARM mode: end photodiode very noisy 2_3f ph 5_ph 5_q ASY BEAM 1_demod

  43. POWER IN THE RECYCLING CAVITY The Variable Finesse Locking Strategy ITF locked on the dark fringe ITF not locked Lock Acquisition “Variable Finesse” of the recycling cavity

  44. POWER IN THE RECYCLING CAVITY The Variable Finesse Locking Strategy Recycled interferometer (~ 17 W) TPR=8% ->Recycling factor ~ 25 Recombined interferometer (~ 60 mW)

  45. The Variable Finesse Locking Strategy Longest Lock: 2h30 Recycling Cavity Power ( Usually about 30-40 minutes ) Need of the linear automatic alignment Lock duration limited by the natural misalignment of the mirrors

  46. The Variable Finesse Locking Strategy • SUMMARY • First lock of the recycled ITF on the end of last October • Stable lock of the recycled interferometer ~ 40-50 minutes • no linear automatic alignment yet  next step • Locking procedure tested several times • lock acquired in few minutes • New original lock acquisition procedure established, combining end photodiodes, frequency servo, 3f-demod signal, slightly misalignement of PR mirror, and lock on the half fringe • 1 day and half of test in the last commissioning run C5

  47. Commissioning Run C5- December 2004 • C5 configurations: • RECOMBINED ITF as in C4 (automatic alignment, laser frequency stabilization servo, OMC locked) • + suspension hierarchical control • -> end of the commissioning of the recombined ITF • RECYCLED ITF (1 day and half)

  48. Best VIRGO Sensitivity Commissioning Run C5- December 2004 RECOMBINED RECYCLED

  49. Recycling cavity control Laser freq control Short michelson control COHERENCES with the GW signal Noise hunting: C5 sensitivity • Sensitivity limited by control noise Longitudinal locking control signal Local control signal BS tx local control

  50. Noise hunting: C5 sensitivity • What about the noise at high frequency ? ? • Observation: noise level change with time i.e. with alignment

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