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VIRGO Superattenuators in next generation detectors S.Braccini, INFN-Pisa on behalf of the Virgo Collaboration. 1) SAT Seismic Isolation: Present & Future. 2) SAT “Passive Control”. 3) SAT Mechanical Glitch Noise. 2. Superattenuator. Magnetic Anti-Spring. 8 m. Blade Springs. 3. 2 Hz.

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VIRGO Superattenuators

in next generation detectors

S.Braccini, INFN-Pisa

on behalf of the Virgo Collaboration


1) SAT Seismic Isolation: Present & Future

2) SAT “Passive Control”

3) SAT Mechanical Glitch Noise

2


Superattenuator

Magnetic Anti-Spring

8 m

Blade Springs

3


2 Hz

Ground

Resonances

f-2N

Transmisson

Frequency (Hz)

Long Pendula

Soft Springs

Mirror

4


2 Hz

Resonances

f-2N

Frequency (Hz)

Large Inertia

Thin Wires

5


Stage by Stage Measurement

Thermal Noise

Ground Seismic Noise

Mirror Residual Seismic Noise

6


DirectMeasurement

SA design

e freccette

7


TF < 1.7 x 10-12

TOP

1.2 x 10-6m Hz-1/2

MIRROR

2 x 10-18m Hz-1/2

8


TF = 1.26 x 10-11

TOP

MIRROR

!

!

9


Upper limitHoriz

Upper limit Vertical

10


Upper limitHoriz

Upper limit Vertical

11


SA design

e freccette

SA design

e freccette

X-Excitation

Experiment

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


Confirmed by direct measurements

Horiz

Vertical

ET

ETx

Horizontal seismic noise dominant

15



Change both number of filters and their distance

(thus varying the total length)

HORIZONTAL

TF

17


HORIZONTAL

5 filters - 15 m

7 filters - 16 m

6 filters - 17 m

6 filters - 14 m

TF

1.8 Hz

18


Upper limitHoriz

Upper limit Vertical

Vertical Attenuation

19


6 Filters (as now)

TF

FILTER @ 310 mHz


CONCLUSION

3rd GENERATION: Use identical technology

with cross-over below 2 Hz

Present SA extension 9 17 m

(1.8 Hz conservative cross-over)

21


1) Seismic Isolation: Present & Future

2) “Passive Control”

3) Mechanical Glitch Noise

22


several microns

mirror swing

23


Accelerometers

DSP

DAC

Actuators

ADC

24


Swing reduction by ID

+

ultra-low freq. passive attenuation

8 m

25


Alignment without

affecting mirror swing

(Payload ad hoc design)

1) Intrinsically diagonalized (Easy control)

2) “Nothing happens” in the off-diagonal world

26




Alignment

transparent for SA

8 m

29




Lock Acquisition

transparent for SAT

8 m


1) Longitudinal swing fraction of mm/s

2) Prealign mirror (fract. of mrads)

(not affecting 1)

3) Lock acquisition

(not affecting 1 - 2)

8 m

4) Reallocation & Tidal Control

(not affecting 1 - 2 - 3)

Residual Swing

LONGITUDINAL: around 100 nm pk pk

ANGLES: fractions of mrad pk pk


500 nrad

RESIDUAL (OPEN LOOP) DISPLACEMENTS

100 nm

SMALL LOCKING & ALIGNMENT CORRECTIONS  LOW NOISE

HIGH ACCURACY: 10 nrads on PR,a few nrads on test masses


RM

AdV

Marionetta

CONTROL NOISE - OK for AdV

35


1) Seismic Isolation: Present & Future

2) “Passive Control”

3) Mechanical Glitch Noise

36


Self-organized criticality dynamics

of dislocations induces a mechanical

shot-noise force (1/f)

37


Potential problem

in last filter(s)

of the chain

38


3 VERTICAL MODES

F7 -Blades

40 Hz

Marionetta

15 Hz

7 Hz

Reference

Mass

Mirror

39


MODES VISIBLE IN DARK FRINGE

Displacement Strain (m Hz^-1/2)

40

Freq (Hz)


TF MEASUREMENT

Blades

Mar

RM

Mir

41


TF MEASUREMENT

Mirror-Beam Displacement (m) / Vertical Force (N)

7 Hz

15 Hz

40 Hz

Freq (Hz)

42


VERTICAL FORCE UPPER LIMIT

z(w) = TF(w) x Fv(w)

7 Hz

40 Hz

Fv_max (w) = z(w) / TF(w)

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

Vertical Force (Upper Limit – N/Hz1/2)

X TF

Freq (Hz)

46


h(f)

Virgo

AdV

1/f noise

upper limit

47


START PARENTHESIS

(just for a betterunderstanding)


F

Vertical Force on Marionetta  MirrorDisplacementalongbeam

z


Closedparenthesis

h(f)

Virgo

AdV

1/f noise

upper limit


Peaks dominated by DAC noise

More stringent upper limits

could be set in VSR3

Model Dependent Approach……

51


Marchesoni et al.

Step

(mean)

Rate

52




Distribution of the differences

1 Hz

0.1 Hz

l> 0.1 - 1 Hz

55


Virgo

AdV

Upper Limit

A FEW UNITS

Stringent Upper Limits (AdV OK)

56


Conclusions

Superattenuators validated for 2° generation

Virgo+ Monolithic Test

Passive Attenuation

Microglitchness

Control Performance

57


Conclusions (3° generation)

Superattenuators validated for 2° generation

9 17 m

(a must also for cross-couplings)

Passive Attenuation

Microglitchness

Control Strategy

More stringent upper limits

(Last stage(s) only)

1) “Passive” strategy decisive

2) Extend hierarchical stages

3) New electronics

(SAFE)

58



The wind problem

MIRRORACTUATION

WIND

SEA

60


Tilt

61


Tiltmeters R&D

10-8-10-9 rad Hz-1/2 @ 30 mHz

62




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