VIRGO LAPP – Annecy NIKHEF – Amsterdam INFN – Firenze-Urbino INFN – Frascati IPN – Lyon INFN – Napoli OCA – Nice LAL – Orsay ESPCI – Paris INFN – Perugia INFN – Pisa INFN – Roma Status of the VIRGO Interferometer S.Braccini – INFN Pisa

Part 1 – Introduction Part 2 – Design Part 3 – Commissioning Part 4 – Future

VIRGO is a typical interferometric GW detector  L    m h   (VIRGO Supernova) L    m

VIRGO is a typical interferometric GW detector h =   gw  = 3· rad

Fabry-Perot cavities to increase the effect Increase beam phase shift by 2F 

Optical Readout Noise 20 W  1 kW An accurate measurement of the phase requires a large amount of photons…

Fluctuation-dissipation theorem Thermal Noise Reduce dissipations in the optical payloads to reduce thermal fluctuations

Seismic Noise Suspend each mirror by a cascade of 6 dof oscillators frequency transmission Ground Seismic Vibrations

Summary of the technique Low Dissipations Fabry-Perot photodiode Recycling High Power Laser Seismic Isolation

Part 2 – VIRGO Design

VIRGO Optical Layout 20 W Laser Input Mode Cleaner (144 m) Output Mode Cleaner (4 cm) Power Recycling Fabry-Perot Cavities (3 km)

VIRGO design sensitivity curve Thermal Shot Seismic

Injection System A few Hz frequency rms stability is achieved in the input beam

Superattenuators Blade springs Magnetic antisprings Extend the band down to a few Hz 6 m

Mirror Ground Displacement (m/Hz 1/2 ) Frequency (Hz) Seismic Isolation Thermal Noise Measured Upper Limit

Pitch Yaw Coil-Magnet Actuators Mirror Local Controls Tens of  rad Fractions of  rad Optical Lever

Resonance Crossing   Mirror Optical Surface MIRROR SWING Photodiode demodulated signal during resonance crossing HOOK CAVITIES AT RESONANCE USING MIRROR COIL-MAGNET ACTUATORS (Picometer Accuracy) Interferometer Locking

Coils Marionetta Mirror Reference Mass Beam Suspension Last Stage Reference Mass Mirror Beam Coils Marionetta

Mirror Ground Displacement (m/Hz 1/2 ) Frequency (Hz) Thermal Noise Seismic Isolation Low Frequency Swing

Fixed Stars ADC DSPDAC Accelerometers Coil-Magnet Actuators Inertial Damping

Fixed Stars Inertial Damping Mirror Optical Surface Mirror swing reduced from several  m/s to a fraction of  m/s Enough to allow locking acquisition

Summary Seismic Noise Suppression above 4 Hz Damp angular swings by local controls (10 -7 rad) to allow a good interference Reduce longitudinal swing by Inertial Damping (0.5  m/s) to allow locking Mirror Optical Surface Pre-Stabilized Beam Source (a few Hz)

Part 3 - Commissioning

RECYCLING CAVITY = l 0 + (l 1 + l 2 )/2 4 degrees of freedom to be controlled (“locked”) l2l2 l1l1 MICHELSON = l 1 - l 2 COMMON ARM LENGTH = L 1 + L 2 L2L2 L1L1 DIFFERENTIAL ARM LENGTH = L 1 - L 2 l0l0 Interferometer Locking

l2l2 l1l1 L1L1 L2L2 l0l0 Variable Finesse Locking Acquisition

L1L1 L2L2 l2l2 l1l1 l0l0 Low Finesse of Recycling Cavity Arm cavity fields do not mix Dark Port DC signal Variable Finesse Locking Acquisition PR Mirror rotated by 100 microrad 50 % Interference (Gray Fringe) Easy preliminary locking (mirror swing is stopped)

Pick-off Laser Frequency follows CARM motion L1L1 L2L2 l2l2 l1l1 l0l0 Dark Port DC signal Variable Finesse Locking Acquisition Put in action the “Second Stage Frequency Stabilization Loop” Common Arm motion is controlled by laser with high accuracy

L1L1 L2L2 l2l2 l1l1 l0l0 Dark Port DC signal Variable Finesse Locking Acquisition Pick-off Laser Frequency follows CARM motion Slow Alignment of the Recycling Mirror

L1L1 L2L2 l2l2 l1l1 l0l0 Dark Port DC signal Variable Finesse Locking Acquisition Slow Alignment of the Recycling Mirror Pick-off Laser Frequency follows CARM motion

L1L1 L2L2 l2l2 l1l1 l0l0 Dark Port DC signal Variable Finesse Locking Acquisition Slide to Dark Fringe

DC-0.01 Hz Tide control Hz 5-50 Hz Hierarchical Control millimiters fractions of micron nm Actuators engender a noise floor proportional to the amplitude of their force range Only nm displacements can be compensated at the mirror level

Use Quadrant Photodiodes to Close Automatic Alignment After Locking…  rad

Single arm Recombined Recycled VIRGO run sensitivities

LIGO and VIRGO

Duty Cycle (%) Time (days) Duty Cycle during C6 run

VIRGO Horizon Horizon NS/NS – Optimal Incidence 1 day

Measure the sensitivity  Identify the noise sources  Try to reduce the noise C6 Improvements Automatic Alignment New Filter for Recycling Control Subtraction of Beam Splitter Control Noise Reduction of laser frequency noise 2kHz bump due to detection tower pump (exciting external bench) Less dynamics for BS correction Noise Hunting

Control Noise Photodiode Noise C7 Run Noise Budget

Incident Beam 12 cm Translations induce beam jitters Recycling Transfer Function The problem of power recycling mirror 350 mm

New monolithic flat power recycling mirror Recycling Transfer Function Old New

Laser Frequency Noise (After Mode Cleaner) Power Recycling Mirror Misaligned Power Recycling Mirror Aligned Suppress back-scattered light Hz Time Faraday Isolator on Input Bench Up to now VIRGO operated with a reduced power (from 7 W down to 700 mW)  Limited Sensitivity in High Frequency Range The problem of back-scattered light

New injection bench

Interferometer locked Interferometer now in action with 7 W input power Faraday isolation ~ 100 (nominally much larger but enough) New Injection Bench Performance Mode Cleaner Transmission signal (Now) Mode Cleaner trasmission signal (Before)

Reduction of sidebands power by a factor ~ 4 (time constants ~ a few minutes) A New Problem - The thermal effect 10 min CARRIER POWER SIDEBAND POWER

A New Problem - The thermal effect Lock is kept for long periods despite of this problem 10 hours SIDEBAND POWER CARRIER POWER 15 min SIDEBAND POWER CARRIER POWER

The Present Status * Interferometer locked for a long period with 7 W input power * 10 dof of automatic alignment controlled * Sensitivity curve measured and noise hunting restarted Just a “technical sensitivity” curve to show that itf restarted C7 Now

Part 4 – The Future

2006: Noise reduction  Reach design sensitivity above 100 Hz 2007: Scientific Run (stop for upgradings ?) 2008: VIRGO+ assembly and commissioning NETWORK AGREEMENT AND JOINT ANALYSIS Plans for next years

Thermal Shot Seismic 50 W laser Monolithic Suspensions VIRGO + Improvements

VIRGO + Design Sensitivity VIRGO + VIRGO DESIGN

First Generation Sensitivity VIRGO LIGO Resonant Antennas 2007 Hz GEO Core 10 Mpc BH-BH Merger 100 Mpc Pulsars h max, 1 year integration BH-BH Inspiral, z = 0.4 BH-BH Inspiral, 100 Mpc QNM from BH Collisions, Msun, z=1 NS,  =10 -6, 10 kpc QNM from BH Collisions, Msun, 150 Mpc NS-NS Inspiral, 300 Mpc NS-NS Merger 100 Mpc Unlikely Detection

h Hz Core 10 Mpc NS-NS Merger 100 Mpc BH-BH Merger 100 Mpc Pulsars max, 1 year integration BH-BH Inspiral, z = 0.4 BH-BH Inspiral, 100 Mpc QNM from BH Collisions, Msun, z=1 NS,  =10 -6, 10 kpc QNM from BH Collisions, Msun, 150 Mpc NS-NS Inspiral, 300 Mpc VIRGO + SFERA (Canceled) DUAL Demonstrator (2011) LIGO+ Likely Detection Upgraded Network ( ) h GEO-HF (2009/10)

Next Generation Advanced Virgo (2012) Design activity still not started R&D activities on High power lasers Signal recycling and optical topologies Coatings Electrostatic actuators

Part 4 - Future Advanced Virgo White Paper VIR – NOT – DIR – 1390 – 304 Beyond 2012

Advanced Virgo Hz Core 10 Mpc NS-NS Merger 100 Mpc BH-BH Merger 100 Mpc SFERA QND Pulsars h max, 1 year integration LCGT-I 3rd Generation ITF BH-BH Inspiral, z = 0.4 BH-BH Inspiral, 100 Mpc QNM from BH Collisions, Msun, z=1 NS,  =10 -6, 10 kpc QNM from BH Collisions, Msun, 150 Mpc Advanced LIGO NS-NS Inspiral, 300 Mpc DUAL SiC SFERA QL Detection is “sure” Beyond 2012

NS/NS hundreds of Mpc ITF Advanced VIRGO-LIGO 2013 VIRGO-LIGO 2006 Virgo

Now: VIRGO is again in action with 7 W input beam Conclusions 2006: End of commissioning 2007: Scientific Run with a sensitivity comparable to LIGO Open Problems: Thermal compensation, Low frequency control noise 1st GENERATION NETWORK IS IN ACTION ! …. VIRGO+ (2009) and VIRGO Advanced ( )

The End

MATRIX Old injection system autoalignment layout Ref. cav. MC mirror Laser M5 M6 Ref. cav. autoalignment MATRIX Injection bench MC mirror autoalignment -- Inj.B. local control -- Beam autoalignment -- IB Coils MC AA Picomotors Piezos Wavefront sensors

MATRIX New injection system autoalignment layout Ref. cav. MC mirror Laser M5 M6 MATRIX RFC AA Beam prealignment MATRIX MC IB AA IB Coils Ref.cav. autoalignment Picomotors Piezos -- Injection bench MC mirror autoalignment -- Inj.B. autoalignment -- Beam autoalignment -- DC position sensors Wavefront sensors

1. Mirror excitation in windy conditions –=> more frequent unlocks when weather is bad 2. DAC noise on mirror actuation coils –High force needed for lock acquisition –=> bad DAC dynamics in steady conditions (low force) Micro-seismic peak (sea waves) Suspension: recent problems seismic acceleration wind speed susp displacement noisy day calm day

Suspension: inertial damping modification L(s) H(s) L+H = 1 accelerometer LVDT Inertial damping –Inverted pendulum top platform is immobilized by –HF accelerometers (inertial sensors) –LF LVDT’s (ground based) => introduce seismic noise Solution –Reduced HF/LF cross-over frequency to 30 mHz –Not so simple... (see G. Losurdo’s talk) LVDT = linear variable differential transformer 30 mHz

Thermal effects 10 min  Reduction of sidebands power by a factor ~4  Time constants ~ a few minutes  Power reduction planned at the beginning of June  Study of the effect by simulation and experimental measurements (scanning Fabry-Perot)

LIGO-Virgo Run Planning The agreement foresee also a run coordination – “A Joint Run Planning Committee will be formed, consisting of the Virgo and LSC Data Analysis Coordinators, plus relevant experts from Virgo, GEO, and LIGO on topics such as: calibration, detector characterization/vetoes, detector planning, commissioning, and site management…” Start sketching a possible joint run planning VERY PRELIMINARY

Part 3 VIRGO Future

CERN – C.A.P.P. workshop – June 16 th, 2003 G.Losurdo – INFN Firenze-Urbino Sensitivity improvement The nominal Virgo sensitivity is dominated by –the shot noise, at high frequency –the pendulum thermal noise at low frequency

VIRGO intende raggiungerla nei prossimi mesi