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State College May 2004 LIGO-
Mining for IMBH Gravitational
Waves
• Fabrizio Barone • Enrico Campagna• Yanbei Chen• Giancarlo Cella• Riccardo DeSalvo• Seiji Kawamura
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State College May 2004 LIGO-
Pushing the Low Frequency Limit of ground based GWIDs
• Three limiting noise sources impede GWID at Low Frequency
1. Newtonian Noise (NN, alias Gravity Gradient)2. Suspension Thermal Noise (STN)3. Radiation Pressure Noise (RPN)
• All three can be reduced by means of an underground interferometer
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State College May 2004 LIGO-
Is gravity gradient going to stop us?
~70 Hz
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State College May 2004 LIGO-
Which knobs to turn for low frequency
• In LG-GWID the first limitation is
• Newtonian noise, followed by
• Suspension thermal noise and
• Radiation pressure noise
Example: surface LF-GWID (R.DeSalvo, Class. Quantum Grav. 21 (2004))
8 Watts laserFused Silica Mirror70 Kg mirrorLonger suspensions
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State College May 2004 LIGO-
LF-GWID the lowest frequency feasible surface GW detector
Bad seismic dayGood seismic day
~30 Hz, possibly 20 Hz
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State College May 2004 LIGO-
Newtonian Noise
• NN derives from the varying rock density induced by seismic waves around the test mass
• It generates fluctuating gravitational forces indistinguishable from Gravity Waves
• It is composed of two parts,1. The movement of the rock surfaces or interfaces
buffeted by the seismic waves
2. The variations of rock density caused by the pressure waves
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State College May 2004 LIGO-
Newtonian Noise
• How to shape the environment’s surface to minimize NN?
• The dominant term of NN is the rock-to-air interface movement
• On the surface this edge is the flat surface of ground
seismic motion leads to
Ground surface
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State College May 2004 LIGO-
Cella Cancellation of NN • If the cavern housing the suspended test mass is shaped
symmetrically along the beam line and around the test mass tilting and surface deformations, the dominant terms of NN, cancel out
– (with the exception of the longitudinal dipole moment, which can be measured and subtracted).
atilting leads to fluctuating attraction force
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State College May 2004 LIGO-
Cella Cancellation of NN • Pressure seismic waves induce fluctuating rock density around the
test mass• The result is also fluctuating gravitational forces on the test mass
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State College May 2004 LIGO-
Cella cancellation of NN• Larger caves induce smaller test mass perturbations• The noise reduction is proportional to 1/r3
• The longitudinal direction is more important =>elliptic cave
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State College May 2004 LIGO-
Cella cancellation of NN
Reductionfactor
Cave radius [m]
5 Hz10 Hz20 Hz40 Hz
Calculation made forCentered Spherical CaveIn rock salt beds
Width Length
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State College May 2004 LIGO-
Newtonian Noise gains
• Minimal (multiplicative) Gains
• ≥ 102 from lower underground activity
• ~ 104 from symmetry and size of cave
• Gain 101.5 in frequency (=> ~1 Hz)
• Now we can try kissing LISA
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State College May 2004 LIGO-
.
Under Ground <|> Above Ground
NN limit
The physics, frequency reach
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State College May 2004 LIGO-
The physics, Universe range
1
10 1
10
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State College May 2004 LIGO-
.Above ground
Ad-LIGO: See LIGO document M-0300023-00LF-GWID: See R.DeSalvo, Class. Quantum Grav. 21 S1145-S1154,(2004)
G. Conforto, Nucl.Instr.Meth. Vol 518/1-2 pp 228-232 (2004)
Limited by Newtonian Noise
Under ground
Aspen presentation, LIGO-G040036-00-R
CEGO proposal, LIGO-T040059-00-R.doc
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State College May 2004 LIGO-
Reducing the suspension thermal noise
• Reduce suspension thermal noise with long suspensions
• Noise ~ 1/√L
• Suspensions tens of meters long
• How to shape the facility to allow this?
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State College May 2004 LIGO-
Vertical cross section
A) Upper experimental halls contain all suspension points, readout and control equipment
B) Wells (50 to 100 m deep allow for long isolation and suspension wires for LF seismic and STN reduction
C) Lower large diameter caves, immune from people’s and seismic Noise reduce the NN
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State College May 2004 LIGO-
• Large symmetric underground halls for NN
• Longer suspension wires for STN
• Large mass mirrors for RPN
• Large beam spots for normal TN
How far can we turn the knobs?
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State College May 2004 LIGO-
For lowest frequencies,
turn more the same
knobs
SuspensionThermal
Violin mode
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State College May 2004 LIGO-
Suspension thermal noise limitations
• Can make one more step improving the materials (silicon instead of fused silica) getting to 3-4 Hz
• After that, cryogenics or alternative solutions will be needed
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State College May 2004 LIGO-
Seismic Attenuation, OKSuspension and Seismic Isolation
schematics
10-20 meter pendulaBetween all stages
2-3 meter tallPre-isolatorIn uppercave
LF Vertical filters marionetta
Composite Mirror
Recoil mass
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State College May 2004 LIGO-
You have never seen a seismic attenuation filter
• Gosh, where do you come from?
• I will show you one!
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State College May 2004 LIGO-
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Filter under test
AttenuatedPayloadwire
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State College May 2004 LIGO-
Mirror design - a way out• A clear no action band is present
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State College May 2004 LIGO-
Summarizing
• An underground facility permits to overcome or reduce Newtonian, Suspension Thermal and Radiation Pressure Noise the three limitations for Low Frequency operation of GWIDs
• Going underground is a very attractive option to explore the IMBH Universe
• Chinese scientists got interested and have proposed to their government the construction of an underground GW detection facility CEGO
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State College May 2004 LIGO-
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State College May 2004 LIGO-