VIRGO Superattenuators in next generation detectors
S.Braccini, INFN-Pisa
on behalf of the Virgo Collaboration
1) SAT Seismic Isolation: Present & Future
3) SAT Mechanical Glitch Noise
2
2) SAT “Passive Control”
Blade Springs
8 m
Superattenuator
Magnetic Anti-Spring
3
Ground
Mirror
Resonances
f-2N
Tra
nsm
isso
nFrequency (Hz)
2 Hz
Long PendulaSoft Springs
4
Resonances
f-2N
Frequency (Hz)
2 Hz
Large InertiaThin Wires
5
Stage by Stage Measurement
Thermal Noise
Ground Seismic Noise Mirror Residual Seismic Noise
6
SA designe freccette
DirectMeasurement
7
MIRROR
2 x 10-18 m Hz-1/2
1.2 x 10-6 m Hz-1/2
TF < 1.7 x 10-12
TOP
8
!!
TOP
MIRROR
TF = 1.26 x 10-11
9
Upper limit Horiz
Upper limit Vertical
10
Upper limit Horiz
Upper limit Vertical
11
SA designe freccette
X-ExcitationExperiment
SA designe freccette
Bypass ? 12
AdV - Seismic Isolation OK
ET - Reduction of low frequency cut-off
13
Stage by Stage TF
Crossing expected @ 2.5-3 Hz 14
Horizontal seismic noise dominant 15
Confirmed by direct measurements
ETx
ET
Horiz
Vertical
16
ETx
ET
PRESENT CROSS-OVER
HORIZONTALChange both number of filters and their distance(thus varying the total length)
17
TF
HORIZONTAL 5 filters - 15 m
18
7 filters - 16 m
6 filters - 14 m
6 filters - 17 m
1.8 Hz
TF
19
Vertical Attenuation
Upper limit Horiz
Upper limit Vertical
6 Filters (as now)
FILTER @ 310 mHz
TF
3rd GENERATION: Use identical technologywith cross-over below 2 Hz
21
CONCLUSION
Present SA extension 9 17 m(1.8 Hz conservative cross-over)
1) Seismic Isolation: Present & Future
3) Mechanical Glitch Noise
22
2) “Passive Control”
several micronsmirror swing
23
ADC DSP DAC
Actuators
Accelerometers
24
8 mSwing reduction by ID+
ultra-low freq. passive attenuation
25
Alignment without affecting mirror swing
(Payload ad hoc design)
1) Intrinsically diagonalized (Easy control)2) “Nothing happens” in the off-diagonal world
26
“Passive strategy” in prealignment (y)
27
“Passive strategy” in prealignment (x)
28
8 mAlignmenttransparent for SA
29
Acquire the locking with no recoil 30
Acquire the locking with negligible recoil 31
8 mLock Acquisitiontransparent for SAT
1) Longitudinal swing fraction of m/s
2) Prealign mirror (fract. of rads)(not affecting 1)
3) Lock acquisition (not affecting 1 - 2)
4) Reallocation & Tidal Control(not affecting 1 - 2 - 3)
8 m
Residual Swing LONGITUDINAL: around 100 nm pk pkANGLES: fractions of rad pk pk
SMALL LOCKING & ALIGNMENT CORRECTIONS LOW NOISE
HIGH ACCURACY: 10 nrads on PR, a few nrads on test masses
100 nm
500 nrad
RESIDUAL (OPEN LOOP) DISPLACEMENTS
35CONTROL NOISE - OK for AdV
AdV
RM
Marionetta
1) Seismic Isolation: Present & Future
3) Mechanical Glitch Noise
36
2) “Passive Control”
Self-organized criticality dynamicsof dislocations induces a mechanical shot-noise force (1/f)
37
38
Potential problem
in last filter(s)of the chain
MirrorReferenceMass
Marionetta
3 VERTICAL MODES
F7 -Blades
7 Hz15 Hz
40 Hz
39
Freq (Hz)
Displacement Strain (m Hz^-1/2)
MODES VISIBLE IN DARK FRINGE
40
TF MEASUREMENT
MirRM
Mar
Blades
41
TF MEASUREMENT
Freq (Hz)
Mirror-Beam Displacement (m) / Vertical Force (N)
7 Hz
15 Hz
40 Hz
42
VERTICAL FORCE UPPER LIMIT
7 Hz
40 Hz
z() = TF() x Fv()
Fv_max () = z() / TF()
43
VERTICAL FORCE UPPER LIMIT
Vertical Force (Upper Limit – N/Hz1/2)
Freq (Hz) 44
VERTICAL FORCE UPPER LIMIT
Vertical Force (Upper Limit – N/Hz1/2)
Freq (Hz) 45
Vertical Force (Upper Limit – N/Hz1/2)
Freq (Hz)
X TF
VERTICAL FORCE UPPER LIMIT
46
Virgo
AdV1/f noise
upper limit
47
h(f)
START PARENTHESIS
(just for a better understanding)
Vertical Force on Marionetta Mirror Displacement along beamF
z
Closed parenthesis
Virgo
AdV1/f noise
upper limit
h(f)
Peaks dominated by DAC noise
More stringent upper limitscould be set in VSR3
51
Model Dependent Approach……
f
skfF
)(
~
Marchesoni et al.
RateStep(mean)
52
15 Hz peak amplitude evolution
Time s
rms
53
Distribution of the differences
54
Distribution of the differences
55
> 0.1 - 1 Hz
1 Hz
0.1 Hz
Virgo
AdV
56
A FEW UNITSUpper Limit
Stringent Upper Limits (AdV OK)
57
Conclusions
Superattenuators validated for 2° generation
Passive Attenuation
Microglitchness
Control Performance
Virgo+ Monolithic Test
58
Conclusions (3° generation)
Superattenuators validated for 2° generation
Passive Attenuation
Microglitchness
Control Strategy
9 17 m(a must also for cross-couplings)
More stringent upper limits(Last stage(s) only)
1) “Passive” strategy decisive2) Extend hierarchical stages3) New electronics
(SAFE)
59
A residual problem
WIND SEAMIRROR
ACTUATION
60
The wind problem
Tilt
61
Tiltmeters R&D
10-8-10-9 rad Hz-1/2 @ 30 mHz
62
SAFE Prototype
63
64
THE END