1 / 56

Status of Virgo experiment Matteo Barsuglia, LAL/CNRS Orsay

Status of Virgo experiment Matteo Barsuglia, LAL/CNRS Orsay On behalf of the Virgo Collaboration TAMA symposium, Feb 18 th 2005. The VIRGO Collaboration. V IRGO is an Italian-French collaboration. ITALY - INFN Firenze-Urbino Frascati Napoli Perugia Pisa Roma. FRANCE - CNRS

Download Presentation

Status of Virgo experiment Matteo Barsuglia, LAL/CNRS Orsay

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Status of Virgo experiment Matteo Barsuglia, LAL/CNRS Orsay On behalf of the Virgo Collaboration TAMA symposium, Feb 18th 2005

  2. The VIRGO Collaboration VIRGO is an Italian-French collaboration • ITALY - INFN • Firenze-Urbino • Frascati • Napoli • Perugia • Pisa • Roma • FRANCE - CNRS • ESPCI – Paris • IPN – Lyon • LAL – Orsay • LAPP – Annecy • OCA - Nice

  3. Virgo site (20km from Pisa, Italy)at European Gravitational Obseervatory (EGO)

  4. Expected Sensitivity Seismic wall at ~ 4 Hz

  5. The VIRGO Interferometer Input Mode Cleaner 144 m long Michelson Interferometer with3 km long Fabry-Perot cavitiesin the arms and Power Recycling Output Mode Cleaner 4 cm long • High quality optics are: • located in vacuum • suspended from multi-stage pendulums Laser 20 W

  6. Vacuum System • Two tubes: 3 km long, 1.2 m in diameter,in vacuum since June 2003, 400 modules • 6 long and 3 short superattenuators towers Central area Towers Tubes

  7. The Suspension System The Superattenuator (SA) is designed toisolate the optical components from seismic activities (local disturbances). Working principle  multistage pendulum Expected attenuation @10 Hz:1014 Residual mirror motion (rms) rotation <1 mrad longitudinal <1 mm

  8. The Top Stage Top of an inverted pendulum: - Inertial damping (70 mHz to 5 Hz) - Possibility to move the suspension point with small forces

  9. Passive Filters • Five seismic filters: • Suspended by steel wires • Vertical isolation by a combination of cantilever springs and magnetic anti-springs

  10. The Local Controls Marionette control:CCD camera, optical levers and fourcoil-magnet actuators: <2 Hz

  11. Fast actuators Reference mass and mirror,four coil-magnet actuators

  12. Injection System IMC RFC

  13. Laser Master Slave • Located on an optical table outside the vacuum • Nd:YAG master commercial CW single mode (700 mW) @1064 nm • Phase locked to a Nd:YVO4 slave (monolithic ring cavity) • Pumped by two laser diodes at 806 nm (40 W power) • Output power: 20 W

  14. Input Mode Cleaner • Triangular cavity, 144 m long, Finesse=1000 • Input optics and two flat mirrors are located on a suspended optical bench • End mirror suspended with a reference massfor actuation • Transmission 50% Injection Bench Mode Cleaner Mirror

  15. Detection System Output Mode-Cleaner • Suspended bench in vacuum with optics for beam adjustments and the output mode cleaner (OMC) • Detection, amplification and demodulation on external bench Suspended bench External bench

  16. Output Mode Cleaner Output Mode-Cleaner • 4 cm long ring cavity • Contrast improvement ~ 10 • Length control via temperature (Peltier element) • Lock acquisition takes 10 min Detection Bench

  17. Photodiodes Output Mode-Cleaner • 16 InGaAs diodes for the main beam (dark port), in air and not suspended • 6 additional photo diodes for control purposes Main beam External bench

  18. Digital Controls • Fully digital control, local and global • Feedback is send with 20-bit DACs @ 10kHz to thesuspensions • The suspension control is performed by dedicated DSPs (one per suspension) • Interferometer signals are acquired with 16-bit ADCs @ 20 kHz. The data is transferred via optical linksto Global Control (dedicated hardware and software that computes correction signals and sends them to the mirror DSPs)

  19. Sensing and Control • Modulation-demodulation • scheme with only one modulation frequency • (6 MHz) to control: • 4 lengths • 10 angles

  20. Data Acquisition and Storage • 16-bit ADCs, up to 20 kHz sampling frequency • Data in Frame format:- full signal (20 kHz)- down-sampled to 50 Hz- down-sampled to 1 Hz (trend data) • Frames available for data monitoringwith ~few sec delay • Current rate: 7 Mbytes/s (compressed) • Raw data buffer ~ 2.5 s

  21. Control room

  22. Current Status Central Interferometer (CITF) • 2001-2002 Commissioning of the central interferometer and the injection system • 2002-2003 Tubes commissioning and final mirror installation • Since September 2003 commissioning of the full interferometer

  23. Commissioning of VIRGO The commissioning of the full detector has been divided into three phases: Phase A (sept 2003 - feb2004): the 3 km long arm cavities separatly Phase B (feb 2004 – summer 2004): recombined Michelson interferometer Phase C (from summer 2004) : Michelson interferometer with Power Recycling (full detector)

  24. Commissioning of the arms • Test the cavity locking, and digital control chain • Test the automatic alignment (with the Anderson technique) • Test the frequency stabilization • Test the locking of the output mode-cleaner

  25. Phase A: the two arm cavities are used separatly, starting with the north arm; North Arm Cavity commissioning West arm misaligned PR misaligned

  26. In October 2003 the North arm cavity was locked on first trial using a control algorithm that was tested before with SIESTA, a time domain interferometer simulation The West arm cavity was locked in December 2003 North Arm Cavity

  27. Recombined Interferometer • Phase B: • Recombined Interferometer • B2 (P) used to control common mode (L1+L2) • B2 (Q) used to control beam splitter • - B1/B1’ used to control differential mode (L1-L2) Recombined locked in February 2004 PR misaligned

  28. Automatic Alignment • Anderson technique: • - Modulation frequency coincident with cavity TEM01 mode • - Two split photo diodes in transmission of the cavity (at two different Guoy phases) • - Four signals to control the 2x2 mirror angular positions (NI, NE)

  29. Automatic Alignment • Alignment control allows to switch off local controls • Power inside the cavities becomes more stable • Installed and tested for the recombined interferometer • Bandwidth ~3 Hz • Residual fluctuations ~0.5 urad rms (1 nrad @ 10 Hz)

  30. 1. The laser frequency is stabilised to the common lengths of thearm cavities (bandwidth ~17 kHz) 2. The arm cavities are stabilised to the reference cavity (bandwidth ~2 Hz) Frequency stabilization The `second stage´ of frequency stabilization

  31. C4 run (june 2004) • Both cavities automatically aligned • BS alignment with local control • Michelson (l1-l2) controlled with ref_quad • Laser frequency stabilized to cavities common mode • Cavities common mode locked to reference cavity • Output mode-cleaner locked to dark fringe • Arms differential mode controlled with OMC transmission • Tide control on both arms

  32. C4-june 2004 (recombined) • Configuration: recombined ITF with 90% complete control system: • - automatic alignment of input beam and beam splitter missing • Duration: 5 days • Test periods at the beginning and at the end of the run (~ 0.5 day) • 9 losses of lock during quiet periods (all understood, one due to an earthquake • in Alaska !) • Longest locked period: ~ 28 h, relatively stable noise level

  33. C4 (recombined) sensitivity 2.5 · 10-20

  34. DAC noise 103

  35. Suspension hierarchical control - I Transfer of the low frequency component of the locking feedback force to the marionette DC-0.01 Hz 0.01-1.5 Hz 1.5-50 Hz • Main difficulty: • Driving of tilt modes when pushing on the marionette •  need for a good diagonalization of the driving

  36. Suspension hierarchical control - II • Transfer of locking force to marionette tested • Crossing frequency ~ 0.5 Hz  1.5 Hz  8 Hz ! • Force applied to the mirror (via reference mass coils) decreased by ~10 Force applied to marionette (a.u.) Force applied to the mirror (a.u.)

  37. After C4, recombined ITF • Almost all the controls running • Noise quite understood • C4/C5 data used for data analysis purposes  in july 2004 lock acquisition trial for the recycled ITF started

  38. Light backscattered by the mode-cleaner Laser Frequency (Hz) Input laser beam ITF reflected beam Power divided by 10 • Solutions: • - Short term: insert attenuator between the IMC and the ITF • - Mean term: insert Faraday isolator (input bench upgrade)

  39. Lock acquisition of the recycled ITF The variable finesse lock acquisition “A recycled ITF with a low recycling factor is similar to recombined interferometer “ • Lock the 4 degrees of freedom of the ITF on the half or white fringe • Bring the interferometer slowly on the dark fringe

  40. Step 1: lock on the half fringe ASY DC POWER MICH ERROR SIGNAL With PR misaligned of 10 urad some light goes in the reflected beam -> Used to lock PR - Lock of the recombined on the HALF FRINGE - Lock of the long arms indipendently with the end photodiodes West arm North arm

  41. Step 2: align the power recycling mirror West transmission_phase Coming from TAMA experience North transmission_phase Ref_3f phase Asy_ DC

  42. Step 3: common mode laser frequency West transmission_phase  diff arm mode LASER Ref_3f phase Pick_off_Phase Asy_ DC

  43. Step 4: reducing the offset Offset : 0.5  0.2 ASY DC POWER MICH ERROR SIGNAL

  44. LASER Step 5: change the error signal for the michelson control DCAC West transmission_phase Ref_3f phase Pick_off_Phase Pick_off_Quad

  45. Step 6: going to the dark fringe Recycling gain big increase: intermediate steps to arrive to the dark fringe ITF on the operating point

  46. Power on beam splitter during lock acquisition Recycling gain ~ 25-30 300 times Recombined interferometer

  47. LASER Switch to a “detection” mode Ref_3f phase prcl Pick_off_Quad mich Pick_off_Phase common arm mode Asy_Quad  diff arm mode

  48. 2.5 hours lock Stored power

  49. C5 run – december 2005 • Recycled ITF • Second stage of frequency stabilization (common mode servo) • output mode-cleaner

  50. Recyled sensitivity Control noises BS and PR Oscillator phase noise (?) ?

More Related