Measurement of Geophysical Effectswith large scale gravitational

interferometersV.N.Rudenko

Sternberg Astronomical Institute, MSU

GGD Workshop 17-18 April 2012, IPGP, Paris (France)

Part II : Technical aspects geodynamical measurements with Virgo

Virgo accuracy limits

• strain δL/L < 10^-16 • tilts ∆α < 10^-13 rad

inner core oscillation effect

• Polar mode (а = 1м) 5·10^-14 rad (theory)

• Translation mode 5·10^-15 rad (measurement)

Sensing of pure gravity field variations

Laser

Can we measure Earth Core Movements with Virgo?

Virgo Mirrors are suspended with a single wire suspension, hence angle α+β is independent from ground tilt and from Laser beam angle γ.

=∂∆∂

+=∆

0

2 2

γ

βα

yL

Ry )(

α β

γL

R

δy

If α,β>10-11rad, Δy>1m

laser

ground

GM – guide mirrorsFM – front mirror, EM – end mirrorDF – driver forceIB – injection bench

γ – tilt deformation

γ

γ

DF DF

g1 g2DF, γart

FM EMnGM

GMGM

( ) ( )( ) ( )

=−

+2≈

++2=+

++≈++≈

∧

∧

21

21

2211 ;

gg

gg

gg

artart

artart

θδβδα

δγδγθδγδγδβδα

θδγδγδβθδγδγδα

gravitational signal !

Principle diagram of tilt ground compensation

α β

α β

IB

Conception of angular measurements (Virgo as angular gravity meter)

- Laser is not suspended: so land angular deformations (tilts of the norm vector) are transferred to

beam deflections ; also there are artificial beam inclinations to lock its position in the mirror’s center ; - all together it composes an “angular noise of the beam” contaminating the gravity plumb line variations.

- A. Measurement of the “sum of internal angles” composed by beam with front and end mirrors filters the “angular noise of the beam”, so again the plumb lines are affected only by gravity force variations

- B. Measurement of a single angle “beam ^plumb line” presents the principle of conventional tilt meter: variations of the gravity force vector can be measured only at the beam deformational angular noise background; one has to find an additional ability to reduce this noise.

Raw strain data from “inverted pendulum” LVDT sensors were processed by LSM-fitting with

theoretical tidal curve.

It results in estimations of - f - virgo transform (scale) factor,

- τ - delay time (phase shift),- ∆l – deform. shift (“lock to lock”)

Virgo strain data

Theoretical curve , experimental curve (raw data) and drift curve for North arm during 13 days VSR-2

0 500 1000 1500 2000 2500 3000 3500-50

0

50

100

Мину ты

м км

Горизонтальные деформ ации и их теоретические кривые ( 22:01 5 2007 )без подгонки начало в октября года

-В направлении с евер юг

-В направлении вос ток запад Зем летряс ение

0 500 1000 1500 2000 2500 3000 3500-120

-100

-80

-60

-40

-20

0

20

40

60

80

Мину ты

м км

Горизонтальные деформ ации и их теоретические кривые ( 21:02 2 2008 ) без обработки начало в м ая года

-В направлении север юг

-В направлении вос ток запад

Sun semi-diurnal S2:

720 min, 2.3148e-5 Hz

Sun diurnal S1:

1440 min, 1.1574e-5 Hz

(+P1+…sK1,mK1)

Moon diurnal O1:

1549 min, 1.0758e-5 Hz

Moon semi-diurnal M2:

745 min, 2.2364e-5 Hz

(+M2+…N2)

relative amplitude d = (aobs/athe) ; phase shift ΔΦ≈2Ωτ experimental estimates d = 1.15 ± 0.03, ΔΦ = 2.4 4.0 deg.

1nstr →1/3 mm

Sun semi-diurnal S2:

720 min, 2.3148e-5 Hz

Sun diurnal S1:

1436 min, 1.1542e-5 Hz

(P1+…sK1,mK1)

Moon diurnal O1:

1549 min, 1.0758e-5 Hz

Moon semi-diurnal M2:

745 min, 2.2364e-5 Hz

(M2+…N2)

(1 nstr → 1 mm/3 )

Main tidal harmonics estimates: periods and amplitudes

VSR-2

0 500 1000 1500 2000 2500 3000 3500 4000-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

Мину ты

м крад

NEНаклоны м арионеты

Tilt of North arm end mirror in compare with theoretical curve

0 500 1000 1500 2000 2500 3000 3500-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

Мину ты

м крад

BMS Повороты зеркала по с игналам локального контроля 21:02 2 2008 от поверхнос ти Зем ли от м ая года

BMS Зеркало

Внеш няя тем пература

. . .WE Теор приливн наклон в напр

. . .NE Теор приливн наклон в напр

. . .NE Теор гориз деформ ации в напр

Angular rotation of BMS mirror (ITF input) along the vertical (normal to beam) axis

Angular effect of the inner core oscillations(amplitude 1 m)

• Plumb line deflection:

10^{-10} rad. , τ = 3.5 h ~ 10^{4} sec. →10^{-8} Hz^{-1/2}

A. “single angle measurement”: Virgo mirror’s angle noise: 10^{-7}-10^{-8} rad. Hz^{-1/2}

• Mutual angle of two plumb line deflection: 10^{-13} rad

B. “sum of internal angles measurement”:Virgo angle noise depends on the level of beam angular noise depression;the required level 10^{-11} rad. Hz^{-1/2}

Method of extracting the right “sum angle variable” has to be addressed (!)

polar inner core oscillation mode estimate

Smylie D.E.

inner core translation modes forecast

inner core translation modes detection

with super conducting gravimeter net (!?)

time evolution of the sample of deformation noise standard A1/2 = σ I in mHz^{-1/2}

5 months series VSR-2 measured time evolution of variance of deformation noise; estimate for upper limit core oscillation amplitude(∆ g)min ≥ g0 (Δa)min/ L ≈ 2, 8 μGal. (in two orders worse the GSGresult)

Literature.

-A.V. Kopaev, V.N. Rudenko, Spectroscopy of vibrations of the Earth by means of gravitational-wave -interferometers, JETP Letters 59 (N9), pp 662-665, 1994.

-V.N. Rudenko, Gravitational free mass antenna as an angular gravity gradiometer. -Phys. Letters A, 223, p. 421-429, 1996.

-Bradaschia C., Giazotto A., Rudenko V.N. et al. A possibility of the Earth gravity field measurements- by free mass gravitational antenna. Frontier Science Series, v. 32, p.343-354, 2000 ,Univ. Acad. Press.Inc., Tokyo.

-Rudenko V.N., Serdobolskii A.V., Tsubono K.. Atmospheric gravity perturbations measured- by a ground-based interferometer with suspended mirrors, Class. Quantum Grav., v. 20, № 2, p. 317-329, 2003.

-Grishchuk L.P., Kulagin V.V., RudenkoV.N., Serdobolskii A.V Gravitational studies with laser beam detectors- of gravitational waves”, Class.Quantum Grav. v.22, (№2995), р 245-269, 2005.

- Gusev A.V., Rudenko V.N., Yudin I.S., Registration of slow geophysical perturbations with gravitational wave interferometers. Measurement Techniques, Vol.59, N4. , 2011 english trans. Springer Science+Business Media,

Items to be studied first

• Alignment technique details:(nonlinear alignm., linear alignm, drivers, marionette etc.)

• Injection bench tilt compensation • Vertical mirror’s shift control circuits

• Tidal calibration: ΔαT ~3 10^{-8} rad, [ 10^{-5}rad.Hz^{-1/2}]

the point is an accuracy of the tidal reconstruction δα = ε Δα, ε = 0.1; 0.01;…. 0,003 (core

effect)

Current Problems

Tidal calibration of the Virgo instrument

• - new software for “mixed (strain + tilt) tidal perturbations”…?

• - reconstruction of the phase information after feed back “lock off” ?

• - filtering a “gravity signal” from deformations and beam jitters..?

• - filtering of vertical shifts..?

Sorry for attention!

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