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Virgo central interferometer: commissioning and engineering runs. Matteo Barsuglia Laboratoire de l’Accelerateur Lineaire, Orsay. Summary. Introduction The central interferometer Operation with a simple Michelson Operation with a recycled Michelson - PowerPoint PPT Presentation
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Caltech, February 12th 1
Virgo central interferometer:commissioning and engineering runs
Matteo Barsuglia
Laboratoire de l’Accelerateur Lineaire, Orsay
Caltech, February 12th 2
Summary
• Introduction
• The central interferometer
• Operation with a simple Michelson
• Operation with a recycled Michelson
• Operation with the full injection system
• E-run programs
• Conclusions
Caltech, February 12th 3
Pisa
Virgo aerial view
Caltech, February 12th 4
Virgo sensitivity
Seismic noise
Thermal noise
Shot noise
Caltech, February 12th 5
Virgo optical scheme
Caltech, February 12th 6
The central interferometer (CITF)
BS
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CITF: goals
• Test all the tehcnical choice during arm construction:
• Suspensions
• Fully digital control chain
• Output mode-cleaner
• Local controls
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Suspensions
Top stage
Last stage
Seismic filters
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Suspension Control
Top stage
Lower suspension stages:
• “marionetta” (from upper suspension stage)
• mirror (from “reference mass”)
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Control Architecture• Completely digital
• LinxOS
• C or C++
• photodiode-read-out 20 kHz
• Control 10 kHz
Global control (PowerPC platform):• read phd signals• algorithm for lock acquisition• linear locking and alignment
For each suspension
DSP• correction sharing• Resonance compensation• local controls
DAC 20 bits
Photodiodes (powerPC platform):• ADC 16 bits• compression dynamics filters
GPS Timing
DOL’s
DOL’s
Caltech, February 12th 11
Local Controls
Output mode-cleaner
• Completely out of vacuum
• CCD camera
• Coarse system, markers (50 mrad)
• Fine system (laser beam, optical lever)
• Control from marionetta (noise filtering)
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Detection system
Suspended detection bench
Output mode-cleaner
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Operation with a simple Michelson
• Superattenuator controllability
• Hierarchical control
• Digital control chain
• Output mode-cleaner
• Control robustness
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Suspension performances
• No excitation of unwanted degrees of freedom
• High robustness to non stationnary noises
• Passive filtering experiment (see Braccini’s talk)
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Michelson locking with top stage
Fast corrections (f > 70 mHz)
Slow corrections (f < 70 mHz)
3.5 mN
Force applied to mirror
No feedback to top stage
with feedback to top stage
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Control robustness• Results from E0 run (72 hours) : ITF continuously locked on dark fringe for more than 51h• 1 unexpected loss of locking, duty cycle > 0.98 %
51 hours
unlocked (bright fringe)
locked (dark fringe)
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OMC locking on dark fringe
Transmitted power
signal
TEM00 TEM00TEM00 TEM00
Contrast improvement ~ 10
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Operation with a recycled Michelson
• Lock acquisition
• Frequency stabilization
• Linear alignment
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Lock acquisition
Caltech, February 12th 20
The lock acquisition problem
modules storage
North tunnel
• Force needed to stop the mirror (finesse = 250)
• maximum force 40 mN (limited by EM noise)
kgmF
mvmNF
20250sec/110
2
Fvmmt 250sec/1sec2
Caltech, February 12th 21
Strategy (I) - enlarge the acting time
modules storage
North tunnel
• Use of an antisymetric trigger
> 50 % open
few % close
• Widening the error signal
Pr_B5_ACq
(Pr_B5_DC)p
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A simulated lock acquisitiontrigger
ITF internal power
Dark fringe speed recycling speed
PR correction WI correction
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A real lock acquisition
Correction PR Correction WI
ITF internal power Dark fringe power
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Frequency stabilization
• crossover ~ 3 Hz
• very aggressive filtering above 13 Hz
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Linear alignment
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Linear alignment - results
ugf ~ 5-10 Hz
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Operation with injection system
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Acquisition detection switch
• Dark fringe control switched from B1p to B1
• Offset between B1p and B1
dark fringe on B1p dark fringe on B1
• Need offset compensation and smooth transition
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Optical characterization
• Input power ~ 2 - 2.5 Watts
• Recycled power (maximum) ~ 240 Watts
• Not coupled light ~ 30 %
• Interferometer contrast:
~ 5 10-4 (before OMC) ,
~ 5 10-5 (after OMC)
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E4 sensitivity
Alignmentcontrolnoise
Laserfrequency
noise
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High frequency noise
Laser frequency noise
Peaks: mirrors + holders
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Intermediate range noise
• mode-cleaner mass TF
• no common mode loop
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CITF e-run program
• 5 e-runs (september 2001-july 2002)
• 72 hours each
• 8 hours shift
• 4 people in shift (1 ITF, 1 laser/injection, DAQ, 1 learner)
• 12 on call sub-system experts
• central building closed, remote control
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Sensitivity evolution during e-runs
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Lock robustness during e-runs
E0 1 (local ctrl fail) 98% ~ 51 h E1 1 (local ctrl fail) 85% ~ 27 hE2 3 (2 ctrl software, 1 vacuum) 98% ~ 41 hE3 4 (1 ctrl software, 3 ctrl tuning) 98% ~ 40 hE4 4 (2 ctrl software, 2 injection) 73% ~ 14 h
Run #losses (in ‘normal’ operation) duty cycle longest lock
Normal operation = no experiments, no special conditions, no calibration
Caltech, February 12th 36
Data acquisition during e-runs
• 20 kHz
• 2 writing processes in paralles
• ~ 4 Mbytes/sec
• 1 Tbyes/e-run
• 3 kind of data streams:
• 20 kHz frames
• 50 Hz
• Trend (1 Hz)
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Run overview – E4 (July 2002)calibration and other special investigations ~ 7 hours
« stable » operation ~ 61 h 30’
calibration
~ 3 h 30’
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Duty Cycle – E4
• Normal operation ~ 61h 30’
• Locked ~ 42h 20’
Duty cycle ~ 73 %
• 6 streams with CITF locked
• longest (5) ~ 14h 30’
• shortest (3) ~ 55’
652 31 4
Duty cycle limited by lock acquisition problems of retroreflected light from ITF to injection system
Caltech, February 12th 39
Investigation groups
• Sources of lock losses
• Suspension motions
• Angular drifts
• Output mode-cleaner
• Calibration
• Angular noise
• Seismic noise
• Acoustic noise
• Noise gaussianity/stationarity
• Glitches
• Lines identification
• Injection system noise
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Lock losses study - example
• burst in the local controls of IB
1 sec
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Offset = 1 ·10 -11
Rms = 9 ·10 -12
Offset = 4 ·10 -14
Rms = 1 ·10 -12
Locking accuracy
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Conclusions - sensitivity
Solutions for frequency noise• Replace MC suspension
• Add “common mode” loop
• Solution for alignment noise• automatic alignment
• filtering of high frequency noise
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Conclusions - I
• Technical choices validated
• superattenuators
• “out of vacuum” local controls with CCD cameras
• digital control chain
• output mode-cleaner and detection system
• Lot of experience
• E-runs program very useful for detetector characterisation
Caltech, February 12th 44
Virgo Planning
• Now:
• large mirror installation
• vacuum leak tests
• new MC suspension
• local control improvements
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Mirror installation I
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Mirror installation II
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