24. June 2004 Andreas Freise Status of VIRGO A. Freise For 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-Urbino Frascati Napoli Perugia Pisa Roma FRANCE - CNRS ESPCI – Paris IPN – Lyon LAL – Orsay LAPP – Annecy OCA - Nice

24. June 2004 Andreas Freise The European Gravitational Observatory Last mirror installed June 2003 Inauguration August 2003

24. June 2004 Andreas Freise Expected Sensitivity

24. June 2004 Andreas Freise The VIRGO Interferometer Laser 20 W Output Mode Cleaner 4 cm long Michelson Interferometer with 3 km long Fabry-Perot cavities in the arms and Power Recycling Input Mode Cleaner 144 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 thickness Substrate losses 1 ppm Coating losses <5 ppm Surface 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, mbar All tower (6 long, 2 short) pumping systems: installed, tested and put in operation, 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 Hz: 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 four coil-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 nm Phase locked to a Nd:YVO 4 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=1000 Input optics and two flat mirrors are located on a suspended optical bench End mirror suspended with a reference mass for actuation Transmission 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 cavity Suppression of TEM 01 by a factor of 10 Length 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 10kHz to the suspensions The suspension control is performed by decicated DSPs (one per suspension) Interferometer signals are acquired with 16-bit 20 kHz. The data is transferred via optical links to 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: November 2003 North arm cavity longitudinally controlled C2: February 2004 North arm cavity with longitudinal and angular control C3: April 2004 Recombined interferometer North arm with second stage of frequency stabilisation C4: June 2004 Recombined 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-demodulation scheme 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 simulation The 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 improved The 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 TEM 01 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 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 the arm 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 laser limits 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 underway Both arm cavities were put into operation, longitudinal and angular control were implemented The injection system and the detection system with both mode cleaners are used routinely during the commissioning 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 implemented The 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 links to 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 monitoring with 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