Status Report

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Status Report

• VIRGO Collaboration
• (Stefano Braccini, INFN Pisa)

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VIRGO

• LAPP Annecy
• INFN Firenze-Urbino
• INFN Frascati
• IPN Lyon
• INFN Napoli

• OCA Nice
• LAL Orsay
• ESPCI Paris
• INFN Perugia
• INFN Pisa
• INFN Roma

VIRGO at EGO Site
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VIRGO Optical Scheme
Input Mode Cleaner (144 m)
3 km long Fabry-Perot Cavities
Laser 20 W
Power Recycling
Output Mode Cleaner (4 cm)
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Injection System
Laser Cavity
Laser Source 20 W NdYVO4 laser (l1.064 mm)
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Injection System
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Mirrors

• High quality fused silica mirrors
• 35 cm diameter, 10 cm thickness, 21 kg mass
• Substrate losses 1 ppm
• Coating losses lt5 ppm
• Surface deformation l/100

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Detection
Photodiodes on Detection Bench
Output Mode Cleaner on Suspended Bench
Output Mode-Cleaner
Beam
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Mirror Suspensions
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Mirror Suspension Control
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Interferometer Locking
0.5 mm/s
MIRROR SWING
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Summary
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After Locking
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ITF Common Mode
Input Mode Cleaner
Stabilize the Laser Frequency on the ITF Common
Mode
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The VIRGO Commissioning
Phase A Commissioning of interferometer arms
Locking achieved on Autumn 2003
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The VIRGO Commissioning
Phase A Commissioning of interferometer arms
Locking achieved on Autumn 2003
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The VIRGO Commissioning
Phase B Commissioning of Recombined ITF
Locking achieved on February 2004
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The VIRGO Commissioning
Phase C Commissioning of Recycled ITF
Locking achieved on October 2004 (see Barsottis
talk)
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VIRGO Sensitivity
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Noise Hunting
Measure the sensitivity ? Identify the noise
sources ? Try to reduce the noise
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A stability problem The Jumps
Power in Recycling Cavity
The interferometer jumps in another meta-stable
state
Appeared after C5 (Retuning)
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A stability problem The Jumps
Induced by mirror misalignments and/or changes
in the photodiode demodulation phases
Recycling Cavity jumps in a different equilibrium
state because of spurious zeros in the error
signal
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Other Problems
Laser Frequency Noise (After Mode Cleaner)
Power Recycling Mirror Misaligned
Hz
Power Recycling Mirror Aligned
Time
Suppress back-scattered light
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Other Problems
Curved Recycling Mirror
Incident Beam
12 cm
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Other Problems
Incident Beam
35 cm
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Next Improvements
Injection Bench Replacement (September 2005)
Power Recycling Mirror Replacement (October 2005)
Close Automatic Alignment (see Mantovanis talk)
Next Run (August 2005)
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VIRGO Data Analysis
Six working groups settled up inside Virgo since
1998
h Reconstruction chair F.Marion (LAPP,
Annecy) Noise analysis data quality chair
J.Y.Vinet (OCA, Nice) Coalescing binaries chair
A.Vicerè (INFN Florence/Urbino) Bursts chair
P.Hello (LAL, Orsay) Periodic sources chair
S.Frasca (INFN Rome) Stochastic background chair
G.Cella (INFN Pisa)
Data Exchange
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Conclusions
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THE END
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Vacuum

• Requirements
• 10-9 mbar for H2
• 10-14 mbar for hydrocarbons
• Vacuum pipe
• 1.2 m diameter
• Baked at 150 C for 1 week or more

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Virgo inside the Central Building
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Laser

• 20 W, NdYVO4 laser, two pumping diodes
• Injection locked to a 0.7 W NdYAG laser
• Required power stability dP/P10-8 Hz-1/2
• Required frequency stability 10-6 Hz1/2

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Input Mode Cleaner

• Mode cleaner cavity filters laser noise, select
  TEM00 mode

Input mode-cleaner curved mirror
Input mode-cleaner dihedron
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Mirrors

• High quality fused silica mirrors
• 35 cm diameter, 10 cm thickness, 21 kg mass
• Figures
• Substrate losses 1 ppm
• Coating losses lt5 ppm
• Surface deformation l/100

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Output Optics

• Light filtering output mode cleaner, 3.6 cm long
  monolithic cavity
• Light detection InGaAs photodiodes, 3 mm
  diameter, 90 quantum efficiency
• Suppression of TEM01 by a factor of 10
• Length control via temperature (Peltier cell)

Detection bench
Output Mode-Cleaner
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Superattenuators

• Inverted pendulum pre-isolation stage
• Cantilever bladesmagnetic antisprings for
  vertical isolation
• 3 actuation points for hierarchical control of
  the mirror inverted pendulum, marionette, recoil
  mass
• First and only attempt to extend the sensitivity
  bandwidth down to a few Hz

Magnetic antisprings
Blade springs
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Passive Isolation performance

• Expected seismic displacement of the mirror (red
  curve) compared with natural seismic noise
• Thermal noise is dominant above 3 Hz
• Isolation sufficient also for advanced
  interferometers
• Active damping of the resonances at the top stage
  level

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ITF Operation Conditions

• Keep the FP cavities in resonance
• Maximize the phase response
• Keep the PR cavity in resonance
• Minimize the shot noise
• Keep the output on the dark fringe
• Reduce the dependence on power fluctuations

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Interferometer control

• Quadrant photodiodes provide the error signals to
  control the angular positions of the mirrors

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Hierarchical Control

• Limited dynamic range requires to split forces
  over more control stages

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Towards the Target sensitivity

• Start of full VIRGO commissioning July 2003
• One cavity locked autumn 2003

• Recombined ITF locked Feb 2004
• Power recycling locked Oct 2004

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Understanding the detector

• Measure the sensitivity ? identify the noise
  sources ? try to reduce the noise

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Expanding the Accessible Universe
Where and how can we reduce the detector noise?
No further suppression

• New materials
• Cryogenic interferometers

• High power laser
• Better optics
• QND techniques

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Advanced LIGO (2009)

• Higher power laser (10 W?180 W)
• New seismic isolation system (active)
• Fused silica suspension wires
• 40 kg sapphire mirrors
• Signal recycling

NS/NS detectable _at_300 Mpc
from LIGO
Virgo/LIGO range
LIGO figures
Adv. LIGO range
by R.Powell
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Advanced Virgo

• Virgo already has advanced vibration isolator
  feasible with minor changes to the current
  detector
• New low dissipation suspension fibers and mirrors
  to reduce thermal noise
• New laser and optics to reduce shot noise
• Possible use of a new optical configuration
  (signal recycling)
• Also GEO600 and TAMA are thinking about 2nd
  generation detector

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Before SSFS

200 Hz
ITF (common mode)
Gc
50 Hz
RFC
MC

B2
300 kHz
ML electronics
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SSFS without RFC
200 Hz
ITF (common mode)
RFC
MC
B2
300 kHz
17 kHz
ML electronics
SSFS electronics
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SSFS with RFC
2 Hz
Gc

200 Hz
ITF (common mode)
RFC
MC

B2
300 kHz
17 kHz
ML electronics
SSFS electronics
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Automatic alignment principle

• Anderson technique
• - Modulation frequency coincident with cavity
  TEM01 mode ( 6.27 MHz)
• - Two quadrants looking at the cavity
  transmission (at two different Guoy phases)
• - Four signals to control the 2x2 mirror angular
  positions (NI NE)

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Automatic alignment results

• Automatic alignment operated on both arms
• - bandwidth 3 Hz
• - control precision 100 nrad rms
• Automatic alignment allows to
• - switch completely OFF local position controls
  on all four cavity mirrors
• stabilize power stored in the cavity
• increase locking duration

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• C1 (November 14-17, 2003) North arm Fabry-Perot
• C2 (February 20-23, 2004) North arm Fabry-Perot
  with automatic alignment West arm Fabry-Perot
• C3 (April 23-27, 2004) North cavity locked with
  Second Stage Frequency Stabilization and
  Automatic Alignment
• C4 (June 24-29, 2004) ITF in recombined mode
  with Suspension Tidal Control and Automatic
  Alignment on both arms, Second Stage Frequency
  Stabilization active and arms common mode locked
  to the Reference Cavity.
• C5 (December 2-7, 2004) ITF in recombined and
  recycled mode.

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_at_ 4.1 Hz lt 6 10e-8
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Digital Camera reads the mirror position in all
degrees of freedom
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Coil-Magnet Actuators
ADC
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