04. november 2004 a. freise a. freise, m. loupias collaboration meeting november 04, 2004 alignment...
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04. November 2004 A. Freise
A. Freise, M. Loupias
Collaboration Meeting
November 04, 2004
Alignment Status
04. November 2004 A. Freise
Overview
Suspended bench External bench
Output Mode-Cleaner
Pre-alignment
Non-linear alignment
Linear alignment
Drift control
Simulation
Hardware
04. November 2004 A. Freise
Pre-Alignment
Suspended bench External bench
Output Mode-Cleaner
Interferometer pre-aligned since more than one year
Nevertheless, some pre-alignment is always necessary:
re-alignment of a single component after an intervention: Procedure as in the beginning. Difficult with low light power (10% input light) but it was already successfully done for the input beam alignment (including automatic beam matching)
manual re-alignment after a long period without (global) control: procedures exist for the recombined IFO and are currently being developed by the detector operation / locking groups
04. November 2004 A. Freise
Non-Linear Alignment
Suspended bench External bench
Output Mode-CleanerNon-linear alignment: every kind of computer algorithm performing alignment of the main optics or the main beam
The current software from the Napoli group canautomatically align the North and West arm cavity using a progressive accuracy (from several 10 urads to less than 1 urad)
Automatically align PR to 2 urad (to be improved)
The software is now regularly used in the detector operation
The next version of the software is planned to also align the input beam and the BS to center the beam on the end mirrors (before the cavity alignment)
Provide a new algorithm for the alignment of full VIRGO which is fully automatic and has a better resolution for the PR
04. November 2004 A. Freise
Linear Alignment
Output Mode-CleanerVIRGO is the only project to employ the Anderson technique
First time this technique is tried for interferometers with suspended mirrors
Expected advantages and disadvantages Signals in transmission of the cavity are comparably `clean’
The different degrees of freedom can be detected with comparable strengths in all output ports
Possibly a larger coupling of noise into the gravitational wave channel
04. November 2004 A. Freise
Frequency Range of Alignment Control
DC: beam positions are defined by reference marks, spot position control, below 0.1 Hz
around the resonance frequencies of the suspension pendulums the beam follows the input beam from the laser bench, differential wave-front sensing, 0.1 Hz to 5 Hz
no active control at the expected signal frequencies
04. November 2004 A. Freise
Quadrant Sensors
Linear Alignment: Differential wave-front sensing
Drift Control: Spot position sensing
04. November 2004 A. Freise
Linear Alignment: Current Status
Suspended bench External bench
Output Mode-CleanerInterferometer until recently used in recombined mode (Recycling mirror is misaligned)
North and West arm cavities are automatically aligned (to the beam) since:
North arm: December 2003
West arm: May 2004
Linear alignment ON is the standard condition, no known problems
Longest continuous lock >32h
04. November 2004 A. Freise
Angular Fluctuations
Residual fluctuations:~ 1 nrad @ 10 Hz~ <1urad RMSLimited by:
input beam jitterresonance peaks of the main suspensions (e.g. 0.6 Hz)
04. November 2004 A. Freise
Problems and Solutions (I)
Suspended bench External bench
Output Mode-CleanerLarge transient when switched from Local Control to Linear Alignment:
problem originates in the low frequency components of the control filters
could be solved by re-arranging the switches and filters in the DSP
Difference between vertical and horizontal readout signals made it impossible to optimize the control matrix:
believed to originate in the readout optics (not completely understood)
can be solved completely by using independant control matrix for Tx and Ty. This requires one extra phase shifter (one electronic board) per detector. Currently a simple phase shifter (cable) is used. A new set of phase shifters are being made by Frascati, they will be ready in two weeks
04. November 2004 A. Freise
Problems and Solutions (II)
Suspended bench External bench
Output Mode-CleanerBeam position on terminal benches was moving
Supports of terminal benches and of the first big lens after the end mirrors have been changed
Beam profile on terminal benches could not be measured because of strong spherical aberration
Two big lenses were replaced by doublets
04. November 2004 A. Freise
Problems and Solutions (III)
Suspended bench External bench
Output Mode-Cleaner
Several problems and changes with respect to the Global Control (see F. Cavalier’s talk tomorrow)
A few minor problems with the Quadrant centering (QaServer), to be fixed by upgrading the software soon
Most common problems were related to detector operation only:
excited suspensions (300 mHz, 600 mHz)
detuned demodulation phases for B7/B8 (1-5 Hz)
04. November 2004 A. Freise
Problems and Solutions (…)
Suspended bench External bench
Output Mode-Cleaner…
04. November 2004 A. Freise
From Recombined to Recycled (I)
Suspended bench External bench
Output Mode-CleanerWe only have one mirror more to control BUT the entire control scheme changes when the PR mirror is aligned:
We CAN NOT use the control for the arm cavities any more because for the new alignment readout the `cavities’ as such do not exist any more
In the recycling state: either we can control all mirrors or we can control none
There are two new readouts to be implemented2 quadrant diodes in the detection lab and 2 quadrant diodes in the laser lab
04. November 2004 A. Freise
Optical Readout
Quadrant readout on B2, B5, B7 and B8
The optical readout has been moved from B1 to B5 for the first implementation
The telescope setup in the detection lab is different from the design due to lack of space, need to design a new telescope
All quadrant diodes are on translation stages: all tested, one broken, can be replaced next week
Gains have to be tuned for the full power
04. November 2004 A. Freise
Linear Alignment Matrix (I)
In total: 8 Gouy phases have to be tuned, 16 demodulation phases to be set.
This yields 32 signals to control 10 degrees of freedom (5 horizontal, 5 vertical).
Control topology (phases+control matrix) has been designed by G. Giordano.
The optical matrix has to be measured to generate two 5x16 control matrices using a 2 reconstruction method.
(Without BS control and drift control)
04. November 2004 A. Freise
Linear Alignment Matrix (II)
Suspended bench External bench
Output Mode-Cleaner
We want to measure the 32x10 matrix in a few minutes:
Requires injecting high frequency lines via the reference mass coils, currently tested by P. Ruggi, requires all coils to be connected to DACs
It might be possible to inject such lines continuously (as calibration lines) to measure the optical matrix online, to be discussed
Matlab software has been written to automatically extract the matrix amplitude coefficients from frame data, currently extended to the full matrix
04. November 2004 A. Freise
From Recombined to Recycled (II)
Suspended bench External bench
Output Mode-CleanerAs soon as the recycling lock has become more `natural’ we can implement Linear Alignment for full VIRGO
The implementation will consist of an very experimental period:
During a recycling lock the optical matrix has to be measured
The misalignment angles can be reconstructed online using a chi^2 algorithm with this (static) matrix inside the Global Control
With these one tries to close Linear Alignment control loops
A stable control should be found by understanding the behavior of the control loops during locking tries and by doing an iterative series of matrix measurements and locking tries
04. November 2004 A. Freise
Global Control Algorithm
Suspended bench External bench
Output Mode-CleanerThe current Alignment algorithm inside the Global Control makes use of all the available features:
The configuration is performed via database objects
Derived channels (triggers, error states, reconstructed angles) are send to the DAQ system
On-the-fly switches allow to change between algorithms by clicking a button
An extended algorithm has to be written for full VIRGO control:
The new channels (error signals, feedback) have to be tested
In addition, the chi^2 reconstruction method must be integrated
04. November 2004 A. Freise
Beamsplitter Control
Suspended bench External bench
Output Mode-CleanerIn the final configuration also the local controls of the Beamsplitter should be switched off
The Beamsplitter motion is associated to the same degree of freedom as the West input mirror, therefore it cannot be controlled independently
Instead a `common’ feedback to BS and WI can be implemented, this requires an additional control loop for the DC position (drift control)
In preparation of this work we have already demonstrated
Sending WI feedback only to BS
Sending `common’ feedback
The drift control of the BS
04. November 2004 A. Freise
Drift Control
beam drifts : injection bench and beam splitter to control 2 axes (DC- 0.1 Hz)
DC
DC
04. November 2004 A. Freise
Conclusion
Output Mode-CleanerFirst implementation of the Anderson technique on a large scale interferometer
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