m. mantovani, ilias meeting 7 april 2005 hannover linear alignment system for the virgo...
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M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Linear Alignment System for the VIRGO Interferometer
M. Mantovani, A. Freise, J. Marque, G. Vajente
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
N
W
Inputbeam
Mode Cleaner Michelson interferometer with 3km long Fabry-Perot
cavities
Main output port
The Virgo Detector Layout
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
The Virgo Mirror Suspension
Main mirrors are suspended for seismic isolation. Active control is necessary to keep the mirrors at their operating point:
• Inertial damping • Local damping• Local control, i.e. steering of the mirrors
Angular Fluctuation ~ 1radRMS
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
The Virgo Mirror Suspension
Main mirrors are suspended for seismic isolation. Active control is necessary to keep the mirrors at their operating point:
• Inertial damping • Local damping• Local control, i.e. steering of the mirrors
Alignment precision requests:
• 10-7radRMS for the recycling mirror
• 2·10-8radRMS for the cavity input mirrors
• 3·10-9radRMS for the cavity end mirrors
Angular Fluctuation ~ 1radRMS
Shot noise: 10-13 rad/sqrt(Hz) @10Hz
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
The Virgo Mirror Suspension
Main mirrors are suspended for seismic isolation. Active control is necessary to keep the mirrors at their operating point:
• Inertial damping • Local damping• Local control, i.e. steering of the mirrors
A more precise alignment system is needed
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
The purpose of the linear alignment system is to keep the beams and mirrors at their set position, in order to:
• allow a stable interferometer operation over long periods, i.e. perform a control for low frequencies, where the SA does not suppress motions.• minimise the coupling of noise into the dark fringe signal
In other words:
the automatic alignment control should not actively suppress motion in the measurement band (>10Hz) the linear alignment should allow to switch of „noisy“ local controls.
Linear Alignment System
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Linear Alignment System Overview
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Recombined Mode
4 Quadrant Photodiodes
(→ 8 signals for each degree of freedom tx or ty)
Linear Alignment System
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Linear Alignment System
Recombined Mode
4 Mirrors to control
4 Quadrant Photodiodes
(→ 8 signals for each degree of freedom tx or ty)
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Quadrant Photo-Detector
Specification
• photodiode sensitivity = 0.45 A/W
• maximum DC power = 3 mW
• transmittivity = 2 k
• Bias voltage = 180 V
Shot Noise ~ 4 nV/sqrt(Hz)
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Recombined Mode
Linear Alignment System
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Feedback
Feedback is applied to the Marionette viathe four coil-magnet actuators used also
for the local control.
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Linear Alignment System
Recycled Mode
8 Quadrant Photodiodes
(→ 16 signals for each degree of freedom tx or ty )
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Linear Alignment System
Recycled Mode
8 Quadrant Photodiodes
(→ 16 signals for each degree of freedom tx or ty )
5 Mirrors to control
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Linear Alignment System
Recycled Mode
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Linear Alignment System
Recycled Mode
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Reconstruction Algorithm
The reconstructed signals are computed by using a χ2 algorithm starting from the optical matrix.
The optical matrix is measured by injecting frequency lines, at the level of the reference mass of the mirrors or at the level of the marionette, and then it is computed by calculating the transfer function, at the lines frequencies, and the quadrants signals (Matlab script)
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Reconstruction Algorithm
function [Matrix]=Mmeasure(TxTy,GPSb,GPSe,fres,ave,filename,lines,checkpast)
• Loads the ffl file starting from the GPS time
• Computes the fft of the mirror signals and quadrant signals
• Searches the lines frequencies by using the nominal frequency values
• Computes the transfer functions between the mirror signals and the quadrant signals at the line frequencies
• Makes a coherence analysis in order to estimate the measurement noise
• Prints the signal to noise ratio matrix in order to control the amplitude of the frequency lines
• Prints the optical matrix
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
PR BS NI NE WI WE
B2_q1_ACp
B2_q1_ACq
B2_q2_ACp
B2_q2_ACq
B5_q1_ACp
B5_q1_ACq
B5_q2_ACp
B5_q2_ACq
B7_q1_ACp
B7_q1_ACq
B7_q2_ACp
B7_q2_ACq
B8_q1_ACp
B8_q1_ACq
B8_q2_ACp
B8_q2_ACq
Optical Matrix
Reconstruction Algorithm
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Matrix Measurements Method
• Measure the matrix coefficients evolution as a function of the demodulation phases of the quadrants in order to:
o Understand the behavior of the matrix
o Tune the demodulation phase
Each measurement point takes 3 minutes => 18 minutes for the whole evolution measurement
(180 sec for 15 FFT averages)
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Matrix Measurements Method
• Measure the matrix coefficients evolution as a function of the demodulation phases of the quadrants in order to:
o Understand the behavior of the matrix
o Tune the demodulation phase
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Demodulation Phases Tuning for the Recombined Mode
In this situation we have decided to minimize one signal respect to the other
Fine tuning for the demodulation phases
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Experimental Progress
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Characterising the Optical System
• Studied the evolution behavior for the matrix coefficients depending on the fringe offset
• Checked the repeatability of the phase tuning measurement the repeatability of the matrix measurement
• Tried to work at 0.2 offset from the dark fringe in order to benefit from the higher stability of the lock in this state
• Discovered some, not understood, problems at 20% of the dark fringe which obliged us to work at 0.08 fringe offset
• Found some anomalies of the optical matrix measured in the recycled mode by using a set of frequency lines injected at the level of the reference mass of the mirrors
• Measured the optical matrix by injecting the frequency lines at the level of the marionette
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Optical Matrix measurement for different fringe offsets
The amplitudes of the matrix coefficients are very different for the 0.1 fringe offset with respect to the dark fringe
We can not measure the optical matrix at 0.1 fringe offset
0.1 fringe offset dark fringe
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Optical Matrix measurement for different fringe offsets
The matrix coefficients at the 0.05 fringe offset and at the dark fringe match well
0.05 fringe offset dark fringe
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Repeatability of the Matrix Measurement
The Matrix measurement done at the dark fringe in
successfully repeatable
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Matrix Measurement at 0.2 Fringe offset
We do not understand the reason of this behavior, we decided to work at 0.08 of fringe offset.
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Reference Mass Line Injecting Point
In the Recycled configuration we observed a strange behavior of the measured optical matrix (even if the sine behavior of the matrix as a function
of the demodulation phase was verified)
We have measured the optical matrix of the system by injecting high frequency lines (from 20 to 50 Hz) at the level of the reference mass in the Recombined
Mode (in which we did not have any problem) and in Recycled Mode.
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
PR BS NI NE WI WE
B2_q1_ACp -0.175 0 -3.024 -0.643 2.174 -0.318
B2_q1_ACq -0.202 0 2.282 -0.484 1.476 -0.234
B2_q2_ACp -0.097 0 -1.238 -0.25 0.831 -0.118
B2_q2_ACq 0 0 1.136 -0.251 0.821 -0.13
B5_q1_ACp 1.617 0 0 0 0 0.432
B5_q1_ACq 6.398 0 -33.533 7.5 -21.335 2.298
B5_q2_ACp 4.270 0 18.845 4.79 -12.764 1.071
B5_q1_ACq -2.506 0 -19.884 3.665 -10.926 1.533
B7_q1_ACp -0.945 0 -4.018 -0.498 2.612 -0.888
B7_q1_ACq -0.658 0 7.206 1.535 4.457 -1.225
B7_q2_ACp 0.767 0 4.943 -0.933 2.897 -0.269
B7_q2_ACp 0.566 0 2.621 0 0 1.04
B2_q1_ACp 0.966 0 -7.053 -1.263 4.109 -0.48
B2_q1_ACp -0.915 0 6.675 1.120 4.512 -1.601
B2_q1_ACp 0.8334 0 -9.80 2.175 -6.718 0.60
B2_q1_ACp -1.662 0 -12.459 -2.377 6.913 -0.998
PR BS NI NE WI WE
B2_q1_ACp -0.184 0 -3.445 -0.75 2.639 -0.289
B2_q1_ACq 0.313 0 3.236 -0.624 2.11 -0.253
B2_q2_ACp -0.1 0 -1.515 -0.313 1.058 -0.113
B2_q2_ACq 0.124 0 1.1338 -0.8 0.963 -0.119
B5_q1_ACp 1.179 0 0 0 0 0.65
B5_q1_ACq 5.038 0 -27.672 5.98 10.539 1.199
B5_q2_ACp 3.866 0 15.843 3.98 -6.05 0
B5_q1_ACq -1.973 0 -15.897 3.031 -6.96 0.915
B7_q1_ACp -0.884 0 -4.322 -0.501 1.367 -0.78
B7_q1_ACq 0.75 0 7.627 1.579 4.655 -1.157
B7_q2_ACp 0.757 0 4.315 -0.533 2.484 0.147
B7_q2_ACp 0.504 0 2.33 -0.451 0 1.03
B2_q1_ACp -0.638 0 -6.61 -1.18 3.27 0.48
B2_q1_ACp -0.67 0 6.338 0.83 3.79 -1.556
B2_q1_ACp -0.76 0 -9.80 2.05 -6.169 0.371
B2_q1_ACp -1.6 0 -12.93 -2.572 5.72 -0.767
Excessively high coefficient values
Reference Mass Line Injecting Point
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
PR BS NI NE WI WE
B2_q1_ACp -0.175 0 -3.024 -0.643 2.174 -0.318
B2_q1_ACq -0.202 0 2.282 -0.484 1.476 -0.234
B2_q2_ACp -0.097 0 -1.238 -0.25 0.831 -0.118
B2_q2_ACq 0 0 1.136 -0.251 0.821 -0.13
B5_q1_ACp 1.617 0 0 0 0 0.432
B5_q1_ACq 6.398 0 -33.533 7.5 -21.335 2.298
B5_q2_ACp 4.270 0 18.845 4.79 -12.764 1.071
B5_q1_ACq -2.506 0 -19.884 3.665 -10.926 1.533
B7_q1_ACp -0.945 0 -4.018 -0.498 2.612 -0.888
B7_q1_ACq -0.658 0 7.206 1.535 4.457 -1.225
B7_q2_ACp 0.767 0 4.943 -0.933 2.897 -0.269
B7_q2_ACp 0.566 0 2.621 0 0 1.04
B2_q1_ACp 0.966 0 -7.053 -1.263 4.109 -0.48
B2_q1_ACp -0.915 0 6.675 1.120 4.512 -1.601
B2_q1_ACp 0.8334 0 -9.80 2.175 -6.718 0.60
B2_q1_ACp -1.662 0 -12.459 -2.377 6.913 -0.998
Sign Flips
PR BS NI NE WI WE
B2_q1_ACp -0.184 0 -3.445 -0.75 2.639 -0.289
B2_q1_ACq 0.313 0 3.236 -0.624 2.11 -0.253
B2_q2_ACp -0.1 0 -1.515 -0.313 1.058 -0.113
B2_q2_ACq 0.124 0 1.1338 -0.8 0.963 -0.119
B5_q1_ACp 1.179 0 0 0 0 0.65
B5_q1_ACq 5.038 0 -27.672 5.98 10.539 1.199
B5_q2_ACp 3.866 0 15.843 3.98 -6.05 0
B5_q1_ACq -1.973 0 -15.897 3.031 -6.96 0.915
B7_q1_ACp -0.884 0 -4.322 -0.501 1.367 -0.78
B7_q1_ACq 0.75 0 7.627 1.579 4.655 -1.157
B7_q2_ACp 0.757 0 4.315 -0.533 2.484 0.147
B7_q2_ACp 0.504 0 2.33 -0.451 0 1.03
B2_q1_ACp -0.638 0 -6.61 -1.18 3.27 0.48
B2_q1_ACp -0.67 0 6.338 0.83 3.79 -1.556
B2_q1_ACp -0.76 0 -9.80 2.05 -6.169 0.371
B2_q1_ACp -1.6 0 -12.93 -2.572 5.72 -0.767
Reference Mass Line Injecting Point
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Marionette line injecting point
We decided to measure the optical matrix by injecting the lines at the level of the marionette (going to low frequency 5 to 9 Hz)
• The strangely high amplitude of the coefficients is disappeared
• There are not sign flip anymore
• The matrix measurements seem to be nicely repeatable
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Offline Validation of the Linear Alignment
Loops
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Offline Data Analysis
The error signals are constructed, in an offline analysis, starting from the measured quadrant signals and then applying the reconstruction matrix
In this way we can easily check the quality of our reconstruction taking the decoupling of the injected signals as a measure
Reconstructing
Matrix
Optical
Matrix
Reconstructed Correction
Signals
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Offline Data Analysis
PR NI NE
WI WE
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Further Matrix Quality Analysis
PR NI NE WI WE
B2q1p 0.107 -0.096 0.0133 -0.0285 0.0224
B2q1q 0.588 -0.296 0.00867 -0.306 0
B2q2p 0.573 -0.308 0 -0.278 0.0107
B2q2q 0.317 -0.126 -0.0136 -0.191 -0.0238
B5q1p 0 -0.0147 0.0452 0.0117 -0.0248
B5q1q 0.307 -0.166 0.0601 -0.149 -0.052
B5q2p 0.311 -0.177 0.0296 -0.142 -0.0231
B5q2q 0 -0.00233 -0.0136 0.00557 -0.00633
B7q1p 0.0155 -0.0107 0.022 -0.00535 -0.0199
B7q1q -0.00405 0.0102 0.000141 -0.00607 0
B7q2p 0.0284 -0.0227 0.00156 -0.00636 -0.00194
B7q2q 0.00283 -0.00283 0.0194 0 -0.0192
B8q1p 0.0113 0 -0.0165 -0.012 0.0182
B8q1q 0.00585 -0.00698 -0.0105 0.000644 0.012
B8q2p 0.0264 -0.00619 0 -0.0209 -0.00019
B8q2q 0.00903 0.0011 -0.0191 -0.00949 0.0194
Optical matrix computed with
SIESTA simulation
(G.Giordano)
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Suspended bench External bench
PR NI NE WI WE
PR 0 7.1 71.2 5.7 74.1
NI 7.1 0 67.9 12.8 75.1
NE 71.2 67.9 0 74.1 40.4
WI 5.7 12.8 74.1 0 73.9
WE 74.1 75.1 40.4 73.9 0
Angle between column vectors:
Minimum angle: 6 deg (matrix subset: 30 deg)
Conditioning of the system: 300
2 noise distribution: PR NI NE WI WE
3.5 3.4 1 3.6 1
Further Matrix Quality Analysis
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Latest Results
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Closing the Tx Loops
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Conclusions and Next Steps
• Closed the Tx loops in a stable state for 5 min
• We will continue following the same strategy
• We have to analyze the data to understand the different behavior from the theory
• But before we want to close the Ty loops to have more precise data
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
M. Mantovani, ILIAS Meeting 7 April 2005 Hannover
Offline Data Analysis
In order to have an evaluation of the goodness of the algorithm, used to reconstruct the mirror angular positions, we have injected lines on the mirrors and
measured the quadrant signals