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