suspensions pisa s.braccini c.bradaschia r.cavalieri g.cella v.dattilo a.di virgilio f.fidecaro...
TRANSCRIPT
![Page 1: SUSPENSIONS Pisa S.Braccini C.Bradaschia R.Cavalieri G.Cella V.Dattilo A.Di Virgilio F.Fidecaro F.Frasconi A.Gennai G.Gennaro A.Giazotto L.Holloway F.Paoletti](https://reader037.vdocuments.net/reader037/viewer/2022110211/56649f005503460f94c1648f/html5/thumbnails/1.jpg)
SUSPENSIONS
PisaS.Braccini
C.BradaschiaR.Cavalieri
G.CellaV.Dattilo
A.Di VirgilioF.FidecaroF.FrasconiA.Gennai
G.GennaroA.GiazottoL.HollowayF.Paoletti
R.PassaquietiD.PassuelloR.Poggiani
Florence-UrbinoE.Cuoco
G.CalamaiG.Guidi
G.LosurdoM.MazzoniR.StangaF.VetranoA.Vicere’
RomeM.BonafedeE.BompianiE.Majorana
P.Puppo P.Rapagnani
F.Ricci
NaplesE.CalloniL.DiFioreM.Varvella
PerugiaP.Amico
L.CarboneF.MarchesoniL.Gammaitoni
M.PunturoH.Vocca
S.Braccini
EGOG.Ballardin
A.GennaiG.GennaroP.LapennaR.Taddei
LIGO-G030017-00-D
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Introduction
Mirror Swing Reduction
Mirror Local Controls
Attenuation Measurements
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Extend the detection banddown to a few Hz
VIRGO GOAL
Ground Seismic Vibrations are very strong below several
tens of Hz
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VIRGO Suspensions
SA designe freccette
Residual seismic mirror vibrationsbelow the thermal noise floor
starting from a few Hz
Ground
Mirror
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SA designe freccette
Seismic Noise 10 -7 f -2 m Hz -1/2
~ 3 10 -15 f -5/2 m Hz -1/2 Mirror Thermal
Displacement
Specification onHorizontal transmission
8 orders of magnitudeattenuation @ a few Hz
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Specification onVertical transmission
SA designe freccette
Seismic Noise 10 -7 f -2 m Hz -1/2
~ 3 10 -15 f -5/2 m Hz -1/2 Mirror Thermal
Displacement
Several orders of magnitudeattenuation @ a few Hz
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Suspension Working Principle
ground
mirror
Horizontal Attenuation
Long Pendula !!!
resonances f -2N
Tra
nsfe
r F
unct
ion
Frequency (Hz)
2 Hz
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SA designe freccette
8 m
Chain maximum horizontalfrequency around 2 Hz
Suspension Working Principle
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Suspension Working Principle
resonances f -2N
Tra
nsfe
r F
unct
ion
Frequency (Hz)
Vertical Attenuation
Soft Springs !!!
ground
mirror
2 Hz
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Suspension Working Principle
SA designe freccette
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3.5 mm
Blade rest shape
Blade shape under load
Load
10 cm
Clamp
37.5 cm
14 cm
375 mm20 mm
Variable
Blade Spring Top View
Blade Spring Side View
Blade Springs
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Mechanical Filter
setting screw
centering wires
crossbar
central column
BladeSprings
magnets
Ktot = Kblades- Kmagnets
Chain maximum verticalfrequency around 2 Hz
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6 m-longInverted Pendulum
Top filter
Pre-Isolator
Ground
Flex Joint
FilterChain
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Pre-Isolator
M
L
Flex joint(elastic element)
L
g
M
kf
2
10
Ultra - low frequency oscillator (30 mHz)
INVERTEDPENDULUM
g
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6 m-longInverted Pendulum
Filter Chain
Ground
Pre-Isolator
F = K x = M x
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Expected Performances
Hor
Ver
1
10 -10
10 -20
1 10 1000.1
Transfer Function
Freq (Hz)
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Crossing point
Expected Residual Seismic Noise
“Seismic Wall”
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Beam Splitter
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SA designe freccette
Top Stage Actuators
3 Lines2.25 Hz4.1 Hz9.8 Hz
Direct Measurement
Central Interferometerused as sensor
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Results forHorizontal Transmission
@ 2.25 Hz5 10e-6
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Results forHorizontal Transmission
@ 4.1 Hz< 6 10e-8
This is only an upper limit !!!
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SA designe freccette
Attenuationby Inverted Pendulum
MeasuredHorizontal Transmission
Ground Seismic Noise
10 -7 f -2 m Hz -1/2
Input Top Seismic Noise
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Top Stage Seismic Noiseon beam direction
7 10-11 m Hz-1/2
Top
Ground
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Residual Mirror Seismic Noise
Input Seismic Noise on Top Stage7 10-11 m Hz-1/2
X
Chain Transmission Upper Limit6 10-8
Upper Limit of Residual Noise4 10-18 m Hz-1/2
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Residual Seismic Noise Upper Limit @ 4.1 Hz
4 10-18 m Hz-1/2
< <Thermal Noise @ 4.1 Hz
9 10-17 m Hz-1/2
!!!
Mirror displacement induced by horizontal seismic noise
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MeasuredVertical Transmission
@ 2.25 Hz1.5 10e-6
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MeasuredVertical Transmission
@ 4.15 Hz< 10e-8
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Top Stage Seismic Noise
2 10-9 m Hz-1/2
Top
Ground
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Residual Seismic Noise Upper Limit @ 4.1 Hz
2 10-17 m Hz-1/2
< <Thermal Noise @ 4.1 Hz
9 10-17 m Hz-1/2
!!!
Mirror displacement induced by vertical seismic noise
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Passive attenuation isenough but ….…....
Chain resonant frequencies (0.1 Hz < f < 2 Hz)
induce tens of microns mirror swings
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Mirror swing reduction
1 – Help locking acquisition
Crossing
Permanence timehas to be small
Mir
ror
Opt
ical
Sur
face
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2 - Allow noiseless controlof the interferometer
Maximum compensation “close tothe mirror” is about one micron
Mirror
Mirror swing reduction
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Specificationsfor mirror swing
rms mirror velocitysmaller than a few tenths
of micron per second
rms mirror displacementsmaller than one micron (on a time scale of 10 s)
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6 m-longInverted Pendulum
Filter Chain
Top stage Fixed Stars
Floor
Inertial Damping
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ADC DSP DAC
Inertial Damping
Coil-Magnet Actuators
Accelerometers
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AccelerometerSignal
Lp Butterworthfilter
Integrator
T
… N Slices
rms rms rmsrms
Inertial DampingStability
N consecutive measurements of rms velocity
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WIPR
BSNI
Distribution of 10 s velocity rms
Inertial DampingStability
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Top-stage RMS
0.01
0.1
1
10
1 10 100
Time (s)
rms
velo
city
(m
/s)
Open Loop Closed Loop
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m/s
H
z -1
/2
Hz
Mirror velocity spectrum
Inverted PendulumSpectral Region
Pendulum Chain Mode
0.45 Hz Mode
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Inverted PendulumSpectral Region
Pendulum Chain Mode
0.45 Hz Mode
Mirror velocity spectrum
m
Hz
0.5 microns per second
f
rms dxfx )(~)( 2
m/s
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Mirror velocity spectrum
Fringe signal
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Actual Contribution to velocity rms is 0.37 m/s
CureBetter crossing
LVDT-Accelerometers in Inertial Damping Loopor Top Stage Control
IP Contribute
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Pendulum Contribute
Actual Contribution to velocity rms is 0.26 m/s
CureDamping from ground based
actuators
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Actual Contribution to velocity rms is 0.13 m/s
CureInertial Damping from Top
0.45 Hz Contribute
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Inverted PendulumSpectral Region
Pendulum Chain Mode
0.45 Hz Mode
Mirror velocity spectrum
m
Hz
0.5 microns per second
f
rms dxfx )(~)( 2
m/s
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SA designe freccette
Is the mirror slow ?
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Is the mirror slow ?
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Is the mirror slow ?
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Mirror Displacement
Rms displacement is afew tenths of m @ 100 mHz
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Mirror SwingSpecifications
rms mirror velocitysmaller than a few tenths
of microns per second
rms mirror displacementsmaller than one micron
on time scales larger than 10 s
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Last Stage
Coils
Marionetta
MirrorReference Mass
Beam
ReferenceMass
Mirror
Beam
Coils
Marionetta
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Digital Camera reads the mirrorposition in all degrees of freedom
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Mirror Angular ControlSpecifications
To reduce angular swings from a few tens of microradiansdown to one microradian
Pitch Swingx
Yaw Swing y
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Angular displacements
x
y
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0.1 1 10 100 1000
rms
angu
lar
disp
lace
men
t (m
icro
radi
ans)
Theta x
Theta y
Angular rms
1 rad
1 10 100 1000
Time (seconds)
0.1
1
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CONCLUSIONS
Vertical and horizontal seismic vibrations induce mirror displacements
smaller than thermal noise even around 4 Hz
The mirror swing amplitude has been decreased within the
specifications
Camera control reduces the angularswings of the mirror down to less than
one microradian