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Virgo commissioning since the end of VSR1
E. Tournefier for the commissioning team
ILIAS WG1, CascinaMarch 5th ,2008
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The end of VSR1: mystery death
• Noise structures (200-300 Hz + 600-1000 Hz) highly non-stationary: depend on the quality of the ITF alignment
realignments
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Mystery noise investigations
• Noise also seen in the suspended injection bench error signals investigations in laser lab, around injection tower (electronics, seismic noise, laser chiller, tapping tests,…) investigations on the injection suspended bench
Guilty = piezo-actuators on the suspended bench
Mechanism:Piezo driver noise => actuator motion => IB shaken => IMC length noise + jitter noise
External injection bench
Laser bench
Suspended bench
Tower window
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Dihedron resonance
Mystery noise = beam jitter
• Solution: low pass filter the signal of the piezo drivers impressive decrease of frequency noise and beam jitter noise (no more) mystery structures disappear from DF
Dark fringe
Frequency noise
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Noise budget at the end of VSR1
Control noises
Shot noise
Environmental noise
Actuacor noise
Eddy currents
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Noise budget now
Control noises Shot noise
Environmental noiseActuator noise
Eddy currents
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Summary
• Control noise reduction:– Longitudinal controls: use a second modulation frequency, noise subtraction,
…– Angular controls: more efficient filters, mirrors centering,…
• Actuator noise:– DAC noise filtering – Magnetic noise: replaced magnets on input mirrors (strength/5.5 + good
polarity)
• Environmental noise investigations– Noise sources: air conditioning (<150 Hz), electronic racks– Path to dark fringe:
injection beam jitter, diffused light on benches, detection/Brewster
• Environmental noise reduction:– Beam jitter reduced– Diffused light mitigation on end benches, improved telescopes – Air conditioning improvement started– Brewster => cryotrap to be installed soon
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Alignment noise reduction
• Post VSR1 alignment noise reductions:– More efficient filters– Mirror centering improved– NI+WI local control noise reduced The alignment noise is below V+ design above 20 Hz
• Ongoing improvements: – Find cleaner signals for BS and input mirrors (under drift control) New end benches and new quadrant on B1p have been installed
8MHz
-> Drift control (10mHz)
-> Drift control
see Maddalena’s talk
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Upgrade of the end benches
• New end benches telescopes + rearrangement – Hoping for better quality alignment signals– Galvos installed at that occasion (centring during science
operation)
– Better telescope helps to reduce diffused light
Remaining problem: quadrant signals polluted by air flux and bench motion
Telescope
Quadrantsetting
Now Virgo+
Galvos
Galvos
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Longitudinal noise reduction
Post VSR1 activities: 1/ Characterization of the ITF response (2 weeks immediately after the run):
- response of actuators (mechanics + electronics) / also a cross check for calibration- optical gains (W/m) : mirror displacement photodiode signals
2/ Improvement of the controls for noise reduction:- adapt filters and driving matrix to the actuator response- adapt the sensing matrix to the optical response- use cleaner signal from the second modulation frequency (8MHz) for MICH control- new filters for marionetta to avoid exciting 16/46 Hz resonances- and: better noise subtraction, more flexible Gc algorithm,…
8MHz
B2_8MHz
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Longitudinal control noise reduction
• Longitudinal control noises are not anymore limiting the sensitivity !• Longitudinal control noises are now limited by environmental noises
– Beam jitter subtraction imlemented for B2_8MHz– Long term solution: reduction of environmental noises
ACqB
mixACpB
Bd
A
MICH
PRCL
_5
__20Sensing for central cavity:New B2 signal (8MHz) + new sensing matrix
ACqB
MHzACpB
D
C
MICH
PRCL
_5
8__2
0
0
-VSR1- now
Environmental noise
error signals control signals
see Gabriele’s talk
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Environmental noises
• Test: switch OFF the air conditioning in ALL buildings (NE,WE, CE, MC) Identifed sources and path to dark fringe
- diffused light from end benches (now almost completely cured)- beam jitter induced by AC in laser lab- diffused light from Brewster/detection induced by Central hall + DAQ room AC
AC ONAC OFF
Central hall AC Water pump of CECleanRooms AC Laser lab
DAQ room (+CE hall)
North End AC
Other identified sources: electronic racks (peaks above 200 Hz)
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0 200 400 600 800 1000 1200 1400
new mount 2"
new mount 1"Y Axis
580 Hz
630 Hz
bench
frequency (Hz)
A.U
.
Beam jitter at the injection
• Mechanical resonances of the Beam Monitoring System mount + PZT seen in dark fringe
Mount + PZT replaced with better one:Move resonances at higher frequencies + they are less easily excited
• Identified vertical/horizontal resonance (~45/18Hz) of the injection bench beam jitter Damping of these resonances under study
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Diffused light at the detection
Detection benchesBS
• Many structures above ~100 Hz are coherent with the motion of the Brewster window
• Tapping tests Brewster is the most sensitive of all vacuum piecesBut difficult to make separate what comes from detection tower and from Brewster
Diffused light / modulation by Brewster? Diffused light by detection bench on tower walls or Brewster link / back into the
ITF?
Dark fringe
Coherence with Brewster Seismometer
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Diffused light at detection port
BSDetection benches
• Investigate the path for diffused light– Diffused light on the tower walls? baffles installed – no visible effect– Diffused light inside the Brewster link? better baffles have been installed
(any effect?)– Light diffused by detection optics?
bench rotation experiment-some unclear effect
– Coupling through the Brewster window? replace it with cryotrap next week
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Diffused light reduction (?) at detection
OB
rot
atio
n 10
0 r
ad
• Indication of light reflected/diffused by the detection bench:Dedicated experiment: rotate the suspended bench by 100 rad
30 Hz and 45 Hz bumps disappeared (related to air conditioning noise in central hall) No clear effect at higher frequenciesOther rotation experiments were not so clear (??)Which is the mechanism?
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‘Brewster noise’ variations with alignment
• Noise varies with the alignment/power on dark fringe• True only above 100 Hz • What about the low frequency which seemed to change with bench
rotation?
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Environmental noise reductions
• Diffused light at end benches well reduced (beam dump + new optics)• Beam jitter reduced (new BMS)• Air conditioning improved inside the DAQ room• Some pumps used for AC are OFF (do not seem needed…)=> Impact of AC well reduced
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New DAQ room air conditioning machine
430
UTA
120
200
70
32
90
60 232.5
119
301
137.5
157
233.
5
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Actuator noise reduction
• Reduction of the mirror actuator electronics noise during VSR1 (arm mirrors)
DACDSP CoilDriverGEmphasis
DeEmphasis DeEmphasis
Emphasis
Air conditioning OFF
Impact of DAC noise reduced:• BS:
– marionetta reallocation now working=> CD gain decreased by 4 (DAC + CD noise
reduction)• Arms:
gain decreased by factor 4 (reduced dynamic)=> new coil driver with several (switchable) low noise sectionsnext step: better emphasis filters
+ Improved measurement of low frequency DAC noise performed
No clear improvement observed…
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Actuator noise now
• Marionetta DAC noise below 20 Hz?• We’ll add some filtering this week, let’s see…
Eddy currents
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Magnetic noise?
• Direct coupling of magnetic noise through the magnets attached to the mirror• Magnetic lines injections, modelling => tentative projection (upper limit)
see Bas’s talk
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Magnetic noise?
• We replaced the magnets of the input towers with less strong ones (/5)+ restored the good polarity
No real improvement observed…
Dec 21st
Mar 3rdAC OFF
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Thermal effects
• Cleaning of the input mirrors was performed at the end of November– Some visual improvement was observed for both
WI mirror : Observation before cleaning : with an halogen lamp coupled to a fiber
some large particules on the coatings center part : a little bit ‘opaque’ (~ Ø1 cm) a lot of condensation points but not on the coating
Observation after cleaning : no more large particles center part : clearer(# Ø1 cm) visual aspect better than before cleaning
– But no clear improvement in the thermal effects:- thermal transient similar to before - increase of the sidebands power ~ 25% only
see Michele’s talk
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Thermal effects
• Before / after cleaning
Sidebands powerDark fringeLocking step
B5, carrier
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Plans before Virgo+ shutdown
• Replace Brewster with cryotrap next week
• Thermal Compensation System installation this month – TCS commissioning
• Understand effect of the magnets replacement (magnetic noise, Eddy currents)– Also replace those of the end mirrors?