Transcript ppt - IN2P3

The 9th annual Gravitational Wave Data Analysis Workshop – December 15-18, 2004 Annecy, FRANCE
Environmental noise studies at VIRGO
Irene Fiori – University and INFN Pisa, Italy
(the Virgo Collaboration)
Summary:
• Environmental contributions to Virgo readout noise (C-runs)
• many sources identified through
coherency analyses with seismic and acoustic sensors
and dedicated tests
• Understanding the noise path through detector
• preliminary results
Coherency Analysis: Low Frequencies (< 1 Hz)
Dark Fringe noise below 1Hz is all seismic:
• Residual seismic motion of mirror suspensions (Super Attenuators)
excited by the site microseismic activity (mainly oceanic microseism)
• Multi-coherence analysis (NAP library, see poster session) :
- tri-axial seismometers in Central bld., North and West terminal blds vs. Dark Fringe
- disentagled contributions of seismicity at different locations along ITF
- correlation terms subtracted
resonances SA
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Coherency Analysis: Higher Frequencies
Watts / sqrt(Hz)
 10 Hz
Dark Fringe coherent with
acoustic/seismic sensors
on some peaks/regions
10
100
Frequency (Hz)
1000
Coherence (DF, microphone and seismometer)
 Major sources identified
through dedicated tests
coherence
Noisy devices:
air conditioning, pumps, racks
NE
10
100
1000
Microphone on laser optics table
Seismometer on laser optics table
Frequency (Hz)
MC
WE
LASER LAB
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VIRGO C1
(single arm)
Central building
Dark
Fringe
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Air Conditioning low/high cycle
RMS acoustic noise in laser lab. microphone
C1
• AC switches to “high power regime” from Monday thr Friday 8:00 – 18:00
• Dark fringe “breaths” at 11. and 14. Hz
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• Broadband acoustic noise in laser lab.
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Turbo-molecular vacuum pumps: sweep test
• 1 pump per SA tower (UHV < 10-9mbar in tower lower section)
• magnetically levitated, rotation speed 400 Hz or 600 Hz
VIRGO – C2
IB tower pump: sweep 600Hz 400Hz
 fundamental and harmonics sweep coherently in dark fringe and seismometer
Dark fringe photodiode
Seismometer
near IB tower
Amplitude
Hz
[Watts/sqrt(Hz)]
600.8
1201.5
1802.5
2403.2
3004.3
3604.5
4806.7
5407.5
6008.0
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2 x 10^-7
1 x 10^-6
4 x 10^-8
8 x 10^-8
3 x 10^-9
2 x 10^-9
6 x 10^-9
2 x 10^-9
8 x 10^-10
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From single-arm to Virgo recombined
• Single-arm (C1, C2): coupling to common noise (i.e. frequency noise) is maximum
• Recombined (C3, C4): common noise suppressed by CMRR factor  0.004
• C4 recombined : laser frequency locked to arms common mode
C1 Single arm
C1
C2
C3
C4
Recombined
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From single-arm to Virgo recombined
• Single-arm (C1, C2): coupling to common noise (i.e. frequency noise) is maximum
• Recombined (C3, C4): common noise suppressed by CMRR factor  0.004
• C4 recombined : laser frequency locked to arms common mode
150 Hz (mirror mount)
C4
C4
Recombined
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231 Hz (water chiller laser)
219 Hz (laser ele. rack)
421 Hz (laser ele. rack)
2402 Hz (turbo pump)
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 Which path for seismic/acoustic noise to dark fringe ?
Acoustic test during C4 run
• Broadband white signal sent to a loudspeaker in laser laboratory,
with 5 levels of increasing intensity
 acoustic noise
increase in laser lab.
up to 50 times the
standard noise floor
at [30, 4000] Hz
 noise increase
in dark fringe
up to 10 times
at [150, 1500] Hz
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Effects of acoustic noise: signals layout
VIRGO C4:
IMC
RC
North arm
LASER LAB.
microphone
loudspeaker
West arm
Acoustic noise
Dark Fringe
Injection SYS:
- Laser clean room: laser, beam forming optics, photodiodes&piezos on non suspended benches, in air
- Input Mode Cleaner: plane concave triangular FP, 144m, reference cavity, suspended, under vacuum
- Alignement: laser on RC (<1Hz), IMC optical axis (<10Hz)
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Effects of acoustic noise: signals layout
 Misalignements of IMC (a,  )
IMC rotation ( )
IMC translation (a)
 Power fluctuations of
MC transmitted beam
RC
LASER LAB.
microphone
loudspeaker
ITF trans. power
Acoustic noise
IMC trans. power
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Dark Fringe
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Which path to dark fringe ?
A look at coherences:
Dark Fringe vs. microphone is low  non linear path
Microphone vs. Dark Fringe
Microphone
Jitter of laser beam
is non compensated
by IMC alignement
control
Microphone vs. IMC(a, )
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IMC
a,
Fluctuations of
IMC trasmitted
Power
Misaligned MC gives
power fluctuations
of transmitted beam
IMC(a, ) vs. IMC out Power
Dark Fringe
Power fluctuations
converts into
ITF readout noise
IMC Out Power vs. Dark Fringe
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Non Linear effects
Effect of misalignements (a, ) of IMC optical cavity :
Opt. axis translation: a 
Etra  E00 (1- ½(a2+  2) + i2a )  Ptra  P(a2,  2)

Coherence: Dark Fringe vs. a,
coherence
Coherence: MC trans. Power vs. a,
Opt. axis rotation:  
a(t)
W0
 (t)
coherence
a, a2
, 2
frequency (Hz)
frequency (Hz)
• Linear components may indicate a static (or low freq.) misalignement of the cavity:
a(t)+ aS
 (t)+S
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
~ +  ~

a
a
S
S
P
~
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Power noise propagation model
Power noise contribution to Sensitivity :
Spn(t) = S
S(t) = sensitivity [m]
S = displacement from the dark fringe
P
= relative power fluctuations
P
P
P
1) Naïve model: S  SRMS
2) More accurate model
S  low freq. part (<50Hz) of S
• C4 sensitivity (S) during acoustic noise injection
• Power noise estimate (S) (Naïve model)
• Power noise estimate (S) (more accurate model)
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Conclusions
• We have identified and characterized seismic/acoustic noise
sources affecting detector sensitivity during Virgo commissioning
through coherency analyses and dedicated tests
• Effects of these sources on Virgo dark fringe reduced, and almost
disappeared (C4), as laser frequency noise reduced when ITF was
operated in the recombined configuration
• A test was performed (C4) to verify the robustness of our injection
system against acoustic noise, by injecting noise 50 times larger
than std. level
• This noise produced a jitter of the beam at the Mode Cleaner input,
which caused disalignemnets of the MC cavity,
and at least partially converted into dark fringe power noise.
• A power stabilization of the MC output beam is currently being
commissioned
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