A Laser gyroscope system to detect gravito-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 detectors VIR-0019E-07 G-Pisa gyrolaser after 1 year of operation and consideration about its use to improve Virgo Inverted Pendulum control VIR-0021A-09 Premininary Analysis of the Gyrolaser G-Pisa VIR-0444A-10 Rotational sensitivity of the G-Pisa gyrolaser, IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 57 pp. 618-622 (2010) doi:10.1109/tuffc.2010.1456 arxiv:1001.0476v1 [physics.optics] Performances of G-Pisa : a middle size gyrolaser, Class. Quantum Gravity 27 084033 (2010) doi:10.1088/0264-9381/27/8/084033 Active control and sensitivity of the G-Pisa gyrolaser, Nuovo Cimento Soc. Ital. Fis. B-Basic Top. Phys., 125 pp. 557-567 (2010) doi: 10.1393/ncb/i2010-10859-5 Measuring 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 2 ring laser gyroscope for nano-rotational motion sensing arxiv:1104.0418v3 [physics.ins-det] Measuring Gravito-magnetic Effects by Multi Ring-Laser Gyroscope arxiv:1106.5072v1 [gr-qc] A laser gyroscope system to detect the Gravito-Magnetic effect on Earth arxiv:1007.1861v1 [gr-qc] Moriond2011 and Neutel 2011 G-Pisa, angular rotation inertial sensor, ringlaser has taken data continuously during SR3 and SR4 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 2
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Sagnac Effect (Electromagnetic waves under the effect of rotation) ct + =2 R+R t + t + =2 R(c- R) ct - =2 R-R t - t - =2 R/(c+ R) 2 4 R L c( t t ) c L 8 2 c A
A Ring Laser in short 5
G-GranSasso Germany, Italy and NewZealand field of interest in function of the sensitivity G ring laser 10-4 10-6 10-8 10-10 10-12 10-14 rad/sec Sidereal day seismology tides geodesy 6 General Relativity
Sagnac signal on the Earth Metric: (Minkowski spacetime+ perturbation) Inertial reference system Co-moving inertial reference system Non-inertial rotating reference system + Null geodesics A GI A GM GI 8 1 4 L c R L c R c R 2 3 cos ûr ûn 8 1 2 sin û û 2 2 3 n 7
Measuring relativistic precessions Comparison of Earth rotation Ω measured with respect to LF (local frame) and distant stars i.e. Ω VLBI : both vectors must be referred to the same reference system Ω Ω VLBI Ω LT Ω GEO Ω REL IERS measurements Lense-thirring and geodetic Geophysical signals and environmental noise Ω VLBI changes in modulus and direction due to LoD variations and polar motion Ω LT-GEO can be assumed constant. Variations are 6 order of magnitude smaller Ω REL relative rotations must be identified and subtracted at low frequency A viable solution: multi-axial ringlaser system 8
G Wettzell, known signals and required accuracy 9
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 of the G-Pisa design, which is less expensive than G in Wettzell and can be adapted to model the tridimensional array. Stability necessary 1 part in 10 10 Relative orientation of the rings important, it must be monitored with nrad precision 10
G-GranSasso 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 11
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 12
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. 13
The G-Pisa design (GEOSENSOR) can be easily adapted to a cube structure Ingeneering work necessary for the octahedral arrangement 14
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 15
It is important to study with more details the Fabry- Perot cavities along the diagonals 16
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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 Ω GEO// + Ω LT// 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. 19