Analysis of the Virgo runs sensitivities Raffaele Flaminio, Romain Gouaty, Edwige Tournefier Summary : - Introduction : goal of the study / Overview on Virgo Commissioning - Analysis techniques using the data taken during Commissioning Runs / Results for C5 run - Analysis techniques using Siesta simulation / Last results Hannover, April 8th, 2005 ILIAS WG1 : 4th meeting
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Analysis of the Virgo runs sensitivities Raffaele Flaminio, Romain Gouaty, Edwige Tournefier Summary : - Introduction : goal of the study / Overview on.
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-April 2004 : C3 (one FP cavity + Auto angular alignment + laser frequency stabilisation)
- April 2004 : C3 (first lock of the Recombined Mode, 2 arms)
- June 2004 : C4 (Recombined + Auto angular alignment + laser frequency stabilisation)
- October 2004 : first lock of the Recycled Mode
- December 2004 : C5 (Recombined + improvements and Recycled)
2 main goals of Commissioning :
• To manage to control the full Virgo (recycled mode) achieved at the end of 2004
• To reach Virgo nominal sensitivity “noise hunting”
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The sensitivity curves of Virgo Commissioning
To reach Virgo nominal sensitivity :
Instrumental noises have to be identified in order to be cured
x 100
recombined
north armnorth arm
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I - First approach :Analysis techniques using the data taken from Commissioning runs
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Method used to identify a noise limiting the sensitivity curve
1. First step : To identify the possible noise sources
Method : to look at the coherence function between the dark fringe signal and other channels (correction signals sent to the mirrors, monitoring signals)
2. Second step : To understand how the noise propagates from the source to the dark fringe signal
Method : to find a mathematical model of propagation
3. Final step : The model is compared to the sensitivity curve
Validation of the analysis : the noise is identified and its propagation mechanism is understood
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Examples of identified noise sources during C4 and C5 :
- C4 & C5 recombined
- C5 recycled
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Recombined locking scheme
Laser0
B1_ACp
+
-
Differential Mode control loop
Dark fringe signal
sensitive to differential displacements
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Laser0
B2
+
-
Beam Splitter
B2_ACq
Recombined locking scheme
B1_ACpDifferential Mode
control loop
Signal reflected
by the ITF
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Laser0
B2
B1_ACp
+
-
Beam Splitter
Laser frequency stabilisation
B2_ACp B2_ACqDifferential Mode
control loop
Recombined locking scheme
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Recombined locking scheme
Laser0
B2
B1_ACp
+
-
Beam Splitter
Laser frequency stabilisation
B2_ACp B2_ACqDifferential Mode
control loop
Reference cavity (sensitive to laser frequency noise)
+
+Common Mode control
loop (low frequency)
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Identification of Beam Splitter longitudinal control noise
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C4 run : Noise Sources
Hz
m/Hz R. Flaminio
Beam Splitter longitudinal control noise (introduced by the locking loop) : 10 - 60 Hz15
Laser0
B2
B1_ACp
+
-
Beam Splitter
B2_ACpB2_ACq
+
+
C4 run : Noise Sources
Beam Splitter longitudinal control noise 16
First step : looking for coherent channels to identify the sources
Coherence function between the dark fringe signal and the correction signal sent to the Beam Splitter
Good coherence up to 50 Hz : noise introduced by the Beam Splitter longitudinal control loop ? 17
Goal : to convert the noise introduced by the Beam Splitter control loop into an equivalent displacement (Differential Mode)
Model : fft(Correction signal) x TF(Actuators) x 2 x 1/32
Second step : Building of a propagation model
Longitudinal correction sent to the
Beam Splitter (Volts)
Actuators
Volts meters
Resonant Fabry-Perot 32 round-trips
Global control
B2 quadrature
Due to geometry of the Beam Splitter
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L (meters)
DAC
DAC
Correction signal (Volts)
Coil Driver
Coil Driver
i (Ampères)
Newton
Electronics of the actuators
Pendulum
Zoom on the actuators
TF(Actuators) = TF(electronics) x TF(pendulum) x K(voltsmeters)
Volts/m1045K
6.0f
1
1)pendulum(TF
425f
1
1)selectronic(TF
6)metersvolts(
2
2
fft : “amplitude spectrum”
TF : “Transfer Function”
C4 sensitivity
Beam Splitter longitudinal control noise model
Conclusion : the model is validated noise is introduced by the Beam Splitter control loop
Final step : The model is compared to the Sensitivity curve
• 10-30Hz : model is 2 times lower than sensitivity
there is another source of noise (Beam Splitter angular corrections)
• 30-50Hz : good agreement between model and sensitivity (Input Bench resonances region, see R. Flaminio’s talk, last WG1 meeting, Jan 2005)
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Remember what happened during C4 ...
Low frequency : C4 sensitivity dominated by Beam Splitter control noise (B2_ACq) and tx angular control noise (sent to the mirror, Sc_BS_txCmir)
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Low frequency : Coherence between control signals and dark fringe signal
1-100 Hz : coherence between B1_ACp and Beam Splitter control signals (longitudinal z + angular tx)
How the contribution of Beam Splitter control noises (z and tx) in sensitivity can be estimated ?
the coherence between the two noise sources (Sc_BS_zCorr and Sc_BS_txCmir) has to be taken into account
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Dark fringe & BS z Correction Dark fringe & BS tx Correction
Computation of BS longitudinal & angular control noise contributions in sensitivity
Notation :
X0 = noise on dark fringe signal
X1 = noise from Sc_BS_zCorr (BS z correction) ; X2 = noise from Sc_BS_txCmir (BS angular correction) ;
X3 = another noise (not coherent with X1 and X2)
Assuming : X0 = a . X1 + b . X2 + c . X3
complex coefficients a and b have to be computed
Method : Solve the following system
where : refers to the complex coherence between the variables X and Y
Then the total contribution of Beam Splitter control noise in sensitivity is given by :
2X2Xb1X2XaX2X
2X1Xb1X1XaX1X
YX 1XX
2X1XbaRe2ba)ACp_1B(fft *22
a)ACp_1B(fft
b)ACp_1B(fft
Individual contribution of BS length control noise
Individual contribution of BS tx control noise
Remark : X0, X1, X2, X3 are normalised
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BS longitudinal (z) & angular (tx) control noise contributions in sensitivity : obtained from coherence functions
txCmir
Input Bench mechanical resonances
BS z Correction
BS_zCorr
txCmir + BS_zCorr
C5 recombined sensitivity
BS z control noise
BS tx angular control noise
m/s
qrt
(Hz)
Common contribution between the 2 sources of noise (z & tx control) has been substracted
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BS longitudinal control noise : Model compared to Coherence computation
C5 recombined sensitivity
model : BS z control noise
Estimation from coherence : BS z control noise
Good agreement for IB mechanical resonances
Same result for C4 and C5 :
Input bench resonances propagated by BS z control loop
Error signal : B2_ACq
Model : fft(Correction signal) x TF(Actuators) x 2 x 1/32
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How do Input Bench (IB) resonances couple into B2_ACq ?
Summary of R. Flaminio’s talk (3rd WG1 meeting, Jan 2005) :
• Mechanical resonances driven by IB local control noise & coil driver noise
produce IMC length variations
• Frontal modulation : if mistuning of modulation frequency with respect to IMC length :