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24. June 2004 Andreas Freise
Status of VIRGO
A. FreiseFor the Virgo Collaboration
European Gravitational Observatory
SPIE Glasgow 2004
24. June 2004 Andreas Freise
The VIRGO Collaboration
VIRGO is an Italian-French collaboration for Gravitational Wave research with a ground-based interferometer.
ITALY - INFN
Firenze-UrbinoFrascatiNapoli PerugiaPisaRoma
FRANCE - CNRS
ESPCI – ParisIPN – LyonLAL – OrsayLAPP – AnnecyOCA - Nice
24. June 2004 Andreas Freise
The European Gravitational Observatory
Last mirror installed June 2003Inauguration August 2003
24. June 2004 Andreas Freise
Expected Sensitivity
24. June 2004 Andreas Freise
The VIRGO Interferometer
Laser 20 W
Output Mode Cleaner4 cm long
Michelson Interferometer with3 km long Fabry-Perot cavitiesin the arms and Power Recycling
Input Mode Cleaner144 m long
High quality optics are:
located in vacuum suspended from
multi-stage pendulums
24. June 2004 Andreas Freise
Main Optics
High quality fused silica mirrors
35 cm diameter, 10 cm thicknessSubstrate losses 1 ppmCoating losses <5 ppmSurface deformation /100 (rms on 150mm) R: <10-4
24. June 2004 Andreas Freise
Vacuum System
Two tubes: 3 km long, 1.2 m in diameter, installed and tested, in vacuum since June 2003, 10-6 mbarAll tower (6 long, 2 short) pumping systems: installed, tested and put in operation, 10-9 mbar
Tubes
Towers
24. June 2004 Andreas Freise
The Suspension System
The Superattenuator (SA) is designed to isolate the optical components from seismic activities (local disturbances). It is based on the working principle of a multistage pendulum.
Expected attenuation @10 Hz: 1014
Residual mirror motion (rms) rotation <1 rad
longitudinal <1 m
24. June 2004 Andreas Freise
The Top Stage
Top of an inverted pendulum: - Inertial damping (70 mHz to 5 Hz) - Possibility to move the suspension point with small forces
24. June 2004 Andreas Freise
Passive Filters
Five seismic filters:
Suspended by steel wires Vertical isolation by a combination
of cantilever springs and magnetic anti-springs
24. June 2004 Andreas Freise
The Local Control
Marionette control:CCD camera, optical levers and fourcoil-magnet actuators: <2 Hz
24. June 2004 Andreas Freise
Fast Control (Global)
Reference mass and mirror,four coil-magnet actuators: >2 Hz
24. June 2004 Andreas Freise
Laser
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
Slave
Master
24. June 2004 Andreas Freise
Input Mode Cleaner
Triangular cavity, 144 m long, Finesse=1000Input optics and two flat mirrors are located on a suspended optical benchEnd mirror suspended with a reference massfor actuationTransmission 50%
Injection Bench
Mode Cleaner Mirror
24. June 2004 Andreas Freise
Detection System
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
Output Mode-Cleaner
24. June 2004 Andreas Freise
Output Mode Cleaner
Output Mode-Cleaner
Detection Bench
4 cm long ring cavitySuppression of TEM01 by a factor of 10Length control via temperature (Peltier element)Lock acquisition takes 10 min, lock accuracy is /60000
24. June 2004 Andreas Freise
Photo Diodes
16 InGaAs diodes for the main beam (dark port)6 additional photo diodes (and 8 split photo diodes) for control purposes
External bench
Output Mode-Cleaner
24. June 2004 Andreas Freise
Control
Fully digital control, local and global
Feedback is send with 20-bit DACs @ 10kHz to thesuspensions
The suspension control is performed by decicated DSPs (one per suspension)
Interferometer signals are acquired with 16-bit ADCs @ 20 kHz. The data is transferred via optical linksto Global Control, a dedicated hard and software that computes correction signals and sends them to the mirror DSPs
24. June 2004 Andreas Freise
Computer Control
Monitoring and control of the detector by scientists and operators using: - 10 workstations - a digital video system
24. June 2004 Andreas Freise
Current Status
Commissioning of the central interferometer and the injection system from 2001 to 2003
Since September 2003 commissioning of the two arms and the full interferometer
At the end of this year the detector is planned to be operated in its final configuration
Scientific data taking starts 2005
Central Interferometer (CITF)
24. June 2004 Andreas Freise
Commissioning of VIRGO
The commissioning of the full detector is divided into three
phases:
Phase A: the 3 km long arm cavities separatly
Phase B: recombined Michelson interferometer
Phase C: Michelson interferometer with Power Recycling
Currently we have completed phase B.
24. June 2004 Andreas Freise
Commissioning Runs
C1: 14.-17. November 2003North arm cavity longitudinally controlled
C2: 20.-23. February 2004North arm cavity with longitudinal and angular control
C3: 23.-27. April 2004Recombined interferometerNorth arm with second stage of frequency stabilisation
C4: 24.-29. June 2004Recombined interferometer with angular control and second stage of frequency stabilisation
Continuous data taking periods are scheduled every second month:
24. June 2004 Andreas Freise
Sensing and Control
Modulation-demodulationscheme with only one modulation frequency (6 MHz) to control:
4 lengths 10 angles
24. June 2004 Andreas Freise
North Arm Cavity
PR misaligned
West arm misaligned
Phase A: the two arm cavities are used separatly, starting with the north arm; control systems are to be installed and tested.
24. June 2004 Andreas Freise
North Arm Cavity
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 simulationThe West arm cavity was locked in December 2003
24. June 2004 Andreas Freise
North Arm Sensitivity
24. June 2004 Andreas Freise
North Arm Sensitivity
Sensitivity limited by frequency noise between 7 Hz and 4 kHz (C1)By reducing the bandwidth of the IMC control loops the frequency noise could be improvedThe noise below 4 kHz (C3) still originates in the injection system but is not fully understood
24. June 2004 Andreas Freise
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)
PR misaligned
Recombined locked in February 2004
24. June 2004 Andreas Freise
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)
24. June 2004 Andreas Freise
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)
24. June 2004 Andreas Freise
Frequency stabilisation
The `second stage´ of frequency stabilisation
The laser frequency is stabilised to the common lengths of thearm cavities (bandwidth ~17 kHz)The arm cavities are stabilised to the reference cavity (bandwidth ~2 Hz)Gains of the frequency control loops are increased
24. June 2004 Andreas Freise
Frequency stabilisation
The pre-stabilisation of the laser frequency was succesfully tested in the central interferometer
The frequency noise of the pre-stabilised laserlimits the sensitivity over a wide range
The second stage required for the designed stability was completed in June 2004
The performance will be tested in the commissioning run (C4) starting today
24. June 2004 Andreas Freise
Present Sensitivity (preliminary)
24. June 2004 Andreas Freise
Conclusions
The construction of VIRGO is finished, the commissioning of the full instrument is underwayBoth arm cavities were put into operation, longitudinal and angular control were implementedThe injection system and the detection system withboth mode cleaners are used routinely during thecommissioning The detector is now used in the recombined mode with automatic mirror alignment and the second stage of frequency stabilisation Starting next week the final configuration including Power Recycling will be implementedThe first scientific data runs are planned for next year
24. June 2004 Andreas Freise
End
24. June 2004 Andreas Freise
Data Acquisition and Storage
16-bit ADCs, up to 20 kHz sampling frequency
Data is transferred via optical linksto workstations and then written to disk in Frame format:- full signal- down-sampled to 50 Hz- down-sampled to 1 Hz (trend data)
Frames available for data monitoringwith 3 s delay
Current rate: 7 Mbytes/s (compressed)
On-site storage on spinning media: - 5 TB for online analysis- 70 TB for offline analysis
24. June 2004 Andreas Freise
Injection System
20 W Nd:YAG master-slave laser
Input mode cleaner: 144 m long ring cavity
Reference cavity: 30 cm long ring cavity, mirrors contacted to a rigid ULE spacer
Both cavities: Finesse=1000
IMC
RFC
24. June 2004 Andreas Freise
Recombined Interferometer
Sensitivity below 300 Hz limited by electronic noise from a temporary sensor setup
24. June 2004 Andreas Freise
Automatic Alignment