a laser gyroscope system to detect gravito-magnetic effect ... · a laser gyroscope system to...
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A Laser gyroscope system to detectgravito-magnetic effect on Earth
(G-GranSasso, INFN Comm. II)
…it is a long story, started inside Virgo, in the near future it will move in a different direction, but it will probably come back for the Third Generation Gravitational Waves antennas
Our Papers and Internal notes• About the use of gyro-lasers in gravitational waves interferometric
detectorsVIR-0019E-07G-Pisa gyrolaser after 1 year of operation and consideration about its use to improve Virgo Inverted Pendulum controlVIR-0021A-09Premininary Analysis of the Gyrolaser G-PisaVIR-0444A-10
• Rotational sensitivity of the G-Pisa gyrolaser, IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 57 pp. 618-622 (2010)
doi:10.1109/TUFFC.2010.1456arXiv:1001.0476v1 [physics.optics] Performances of ‘G-Pisa’: a middle size gyrolaser, Class. Quantum Gravity 27 084033 (2010) doi:10.1088/0264-9381/27/8/084033Active control and sensitivity of the “G-Pisa” gyrolaser, NuovoCimento Soc. Ital. Fis. B-Basic Top. Phys., 125 pp. 557-567 (2010) doi: 10.1393/ncb/i2010-10859-5Measuring the Virgo area tilt noise with a laser gyroscope, 46th Rencontres de Moriond and GPhyS Colloquium on Gravitational Waves and Experimental Gravity (2011)
• arXiv:1108.3236v1 [physics.ins-det]A 1.82 m
2ring laser gyroscope for nano-rotational motion sensing
arXiv:1104.0418v3 [physics.ins-det]Measuring Gravito-magnetic Effects by Multi Ring-Laser GyroscopearXiv:1106.5072v1 [gr-qc]A laser gyroscope system to detect the Gravito-Magnetic effect on EartharXiv:1007.1861v1 [gr-qc]
• Moriond2011 and Neutel 2011
G-Pisa, angular rotation inertial sensor, ringlaser has taken data continuouslyduring SR3 and SR4
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G-Pisa will be soon be moved to our
Lab in Pisa, and in 2012 we will
complete the analysis of the data
Taken at the Virgo site
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Sagnac Effect (Electromagnetic waves under
the effect of rotation)
L c t tR
c
L
cA
( )4
28
2
ct-=2R-Rt
-t-=2R/(c+R)
ct+=2R+Rt
+t+=2R(c-R)
A Ring Laser in short
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G-GranSassoGermany, Italy and NewZealand
field of interest in function of the sensitivity
tides General Relativityseismology geodesy
10-4 10-6 10-8 10-10 10-12 10-14
“G” ring laser
rad/sec
Sidereal day6
Sagnac signal on the Earth
Metric: (Minkowski spacetime+ perturbation)
Null geodesics+
Inertial reference system
Co-moving inertial reference system
Non-inertial rotating reference system
n322nr32uusin
Rc
GI
Rc
GM21
L
A8uucos
Rc
GI41
L
A8
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Measuring relativistic precessions
ΩVLBI changes in modulus and direction due to LoD variations and polar motion
A viable solution: multi-axial ringlaser system
• Comparison of Earth rotation Ω measured with respect to LF (local frame) and distant stars i.e. ΩVLBI : both vectors must be referred to the same reference system
RELGEOLTVLBI ΩΩΩΩΩ
Lense-thirring and geodetic Geophysical signals and environmental noiseIERS measurements
ΩLT-GEOcan be assumed constant. Variations are 6 order of magnitude smaller
ΩREL relative rotations must be identified and subtracted at low frequency
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G Wettzell, known signals and required accuracy
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Key points of the apparatus
• Each rings should be larger than 16m perimeter, 24m is a good compromise.
• Zerodur Blocks of this size are not available.
• We propose to use a modular ring, an evolution ofthe G-Pisa design, which is less expensive than G in Wettzell and can be adapted to model the tri-dimensional array.
• Stability necessary 1 part in 1010
• Relative orientation of the rings important, it mustbe monitored with nrad precision
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•3 rings are the minimum, but 6 is a good choice to have redundancy, which can be used to cross check and control of the systematic errors (backscatter noise)
•Cube: 6 independent rings, 24 mirrors •Octahedron: 3 rings with 6 mirrors, each mirror is part of two rings
G-GranSasso
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UnderGround laboratory
LNGS has excellent qualities since it is very deep and has a very high termal stability
Other sites can be considered as well
LNGS has two close VLBI stations: Medicina and Matera
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Quiet locations for the experiment are in general preferable
It is a well known fact that LNGS has a rather high seismicity. A recent study by Wasserman
and Igel have shown that only horizontal motions are high, the vertical one is as expected for a
quiet site. A possible explanation is that the high seismicity comes from the air flux; which can
be cured by closing the tunnel with special doors.
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The G-Pisa design (GEOSENSOR) can be easily adapted to a cubestructure
Ingeneering work necessary for the octahedral arrangement
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The beauty of an Octahedron
several constrains
relative angle between rings /2
3 linear Fabry-Perot along the diagonals, relative angles monitoring
‘6 rings are feasible
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It is important to study with more details the Fabry-Perot cavities along the
diagonals
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Conclusions…so far
• Large ring-lasers are approaching the sensitivity goal of 7X10-14
rad/s (1 day of integration)• IERS gives LoD with a relative error of few x 10-10 enough to estimate relativistic effects (a factor 10 improvement with VLBI2010, Wettzell the first station of this kind, expected operative in 2012, whole network expected operational in 2015)• Symmetry and redundancy → help to control geometry over long time periods (years)• To estimate |Ω| and ΩGEO//+ ΩLT// no need of absolute orientations of the cube edges with respect VLBI reference frame • Measure the parallel component at 10% accuracy after 3 months• 1% accuracy seems feasible (2-3 years)•LNGS is in principle a good location for this experiment, node B in particular•In 2012 we will continue our work as G-GranSasso, INFn Comm II.
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