NOISE IN RESONANT BARS
description
Transcript of NOISE IN RESONANT BARS
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Hannover, 24 September 2004
NOISE IN RESONANT BARSNOISE IN RESONANT BARS
Massimo Visco for ROG Collaboration
CNR - Istituto di Fisica dello Spazio Interplanetario- Roma INFN – Sezione di Roma2
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NOISE IN RESONANT DETECTORSNOISE IN RESONANT DETECTORS
L
GW
TRANSDUCER AMPLIFIER
Mechanicalvibration
Electrical signal
Low noise amplifier(SQUID)
Electronic noiseSeismic noise
Mechanical filters Low and ultralowtemperature
Thermal noise Cosmic ray noise
Veto
DATA Matched Filtering
K( f )S( f )e i2ft0
N( f )
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The mass must be as large as possible The sound speed must be as large as possible (i.e. once the frequency is fixed the detector linear dimensions must be the largest possible)
The sensitivity depends on the orientation between the wave and the axis of the bar
)2(cossin
)(
cos)( 242
020
0
2
Q
QvMt s
CROCROSSSS SESECCTIOTIONN
Antennamass
Soundspeed
Resonancecurve
Direction Polarization
The cross section is sharply peaked at the resonant frequency
/0
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First stage
Second stage
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-70
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10
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10 100 1000 10000
frequency (Hz)
ve
rtic
al a
tte
nu
ati
on
(d
B)
-70
-60
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0
10
20
10 100 1000 10000
frequency (Hz)
vert
ical
att
enu
atio
n (
dB
)
-70
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10
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frequency (Hz)
ho
rizo
nta
l att
enu
atio
n (
dB
)
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10
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10 100 1000 10000
frequency (Hz)
ho
rizo
nta
l att
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n (
dB
)
• Vertical direction • Horizontal direction
1
stage
1
stage
2
stage
2
stage
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AURIGA SUSPENSIONSAURIGA SUSPENSIONS
Transducer
Electronics wiring support
LHe4 vessel
Al2081 holder
Main Attenuator
Compression Spring
Thermal Shield
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The construction of a cryogenic suspensions column
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Electronic noise of the accelerometer
C shaped springs modes
at 600 Hz attenuation > 140dB (theoretical 186 dB)
Accelerometer over the holder
Accelerometer bottom of the column
m/Hz1/2
500 1000 1500 2000
1E-15
1E-14
1E-13
1E-12
1E-11
1E-10
1E-9
frequency (Hz)
Holder modes
No lines 690-1250 Hz
Columns modes up 180 Hz
disp
lace
men
t (m
)
Titanium springs
m/Hz1/2
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Cosmic ray detector
Cylindrical bar
Cosmic ray detector
Rotatingplatform
SQUID electronics
SQUIDamplifier
Transducer
Cryostat
Dilution refrigerator
CRIOSTATO DI NAUTILUSCRIOSTATO DI NAUTILUS
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Antenna
Copper shields
Thermal contact1K Pot
Still
Heat exchanger I
Heat exchanger II
Mixing chamber
Copper cable
DILUTION REFRIGERATORDILUTION REFRIGERATOR
• NAUTILUS and AURIGA bars are the largest mass ever cooled below 1K (145 mK)
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The liquid (the concentrated 3He phase) is lighter and floats on a 4He sea, in equilibrium with the 6.5% “vapor”. When 3He passes from the low entropy liquid to the vapor phase (high entropy) it expands and absorbs heat.
Q
3He out
3He
4He
33He-He-44He Dilution RefrigeratorHe Dilution Refrigerator
Mixing chamber
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Thermal contacts and acoustic isolation
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229
22
2
21064.7
/)cos(
)2/)cos(sin(sin
9
4
GeV
KfWx
LR
Ll
L
z
dx
dW
vLE
o
ooo
2 R
L
lozo
o The longitudinal mode of vibration of the antenna is excited by the thermal expansion due to the energy lost by the particles
Energy lost
Grüneisen coefficient
density sound velocity
Calculation for Nautilus
EFFECT OF COSMIC RAYS ON A EFFECT OF COSMIC RAYS ON A RESONANT DETECTORRESONANT DETECTOR
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Average
11.5 mK
P.Astone et al.: “Cosmic rays observed by the Resonant Gravitational wave detector Nautilus" Physical Review Letter, 84, (2000)14-17
• The first analysis confirmed the calculation made by several authors.
58 K87 TeV
time (s)
(K)
threshold
• Detection of very large unexpected events.
P.Astone et al.: ”Energetic Cosmic Rays observed by the resonant gravitational wave detector NAUTILUS" , Phys. Letters B 499, Feb 2001 16-22
(x 5000)
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0.01
0.1
1
10
100
0.001 0.01 0.1 1 10
Solo T < 1 Kelvin
predizioniEv/Giorno Nautilus 98Nautilus 2000 T<1 K
Eve
nti
/gio
rno
dis
trib
inte
gra
le
Sqrt(Kelvin)
T<1KT<1K
Eve
nt r
ate
(day
-1)
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0.001
0.01
0.1
1
10
100
0.001 0.01 0.1 1 10
Explorer ev/giorno tutto 2003
predizioni
EXPLORER 2002 >600 P M2
Nautilus 2003 ev giorno
Nautilus 2000-2001 ev/giorno
Eve
nti
/gio
rno d
istr
ib in
tegra
le
Sqrt(Kelvin)
Solo T > 1 Kelvin
T> 1KT> 1K
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COSMIC RAY INTERACTION COSMIC RAY INTERACTION WITH NAUTILUSWITH NAUTILUS
Mode energy threshold (K)
events/day (muons)
events/day (hadron)
events/day (EAS)
events/day (multi had.)
events/day (total)
10-2 0.002 0.035 0.04 0.18 0.18 10-3 0.18 0.56 0.24 1.2 2.18 10-4 1.2 6.2 1.3 3.7 12.4 10-5 12.7 55.7 7 5.5 80.9 10-6 155 463 35 653 10-7 1540 3310 137 4987
72 streamer chambers (6x6)m
30 streamer chambers (2.5x6)m
Antenna
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Thermal noiseSF = MkTr/Q
Electronic noiseVn; In Tn=√Vn
2In2 /k
The mechanical oscillator
Mass MSpeed of sound vs
Temperature TQuality factor Q
Res. frequency fr
The transducer
Efficiency
The amplifier
Noise temperature Tn
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• For the read-out of resonant detectors SQUID amplifiers were widely used, to avoid the second stage noise a double squid amplifier is required
NEW AMPLIFIERNEW AMPLIFIER
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•An alternative possible read-out is one based on a Back Action Evading scheme
Trento(2 stage)
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• There are two intrinsic sources of noise that cannot be avoided
-Thermal noise-Electronic noise
HOW THE DIFFERENT SOURCES OF NOISE HOW THE DIFFERENT SOURCES OF NOISE CONTRIBUTE TO THE OVERALL CONTRIBUTE TO THE OVERALL
SENSIVITY?SENSIVITY?
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NOISE CONTRIBUTION INNOISE CONTRIBUTION IN BAR DETECTORS BAR DETECTORS
0.4 0.6 0.8 1 1.2 1.41 10 71 10 61 10 51 10 41 10 3
0.010.1
1
10100
1 1031 104
SignalNarrow-band
Noise
SNR
• The signal and the narrow-band noise have similar shape. If we consider only narrow band- noise the bandwidth is infinite .
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0.4 0.6 0.8 1 1.2 1.41 10 71 10 61 10 51 10 41 10 3
0.01
0.1
110
1001 1031 104
Narrow-band Noise
wide-band Noise
Q0
SNR
When the wide-band noise is not negligible the bandwidth of the detector depends on the ratio between wide and narrow band noise ():
Signal
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SENSITIVITY OF BAR DETECTORSSENSITIVITY OF BAR DETECTORS
h~
nTf
• The “peak” sensitivity depends on “physical” parameters (T,M,Q). To increase the overall sensitivity a larger bandwidth f is required. It can be obtained decreasing the electronics noise contribution and increasing the energy transfer.
• The sensitivity of a detector is usually given in terms of the noise spectral density referred to the input of the antenna
QM
Th e~
S h (1
/Hz)
ffh
hg
r
)(~
min
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To improve the sensitivity peak sensitivity (monochromatic, pulse and stochastic background) we need:
• Large mass• Reduce the thermodynamic temperature • Increase the quality factor
To improve the bandwidth (monochromatic, pulse and stochastic background) we need:
• Increase the coupling • Reduce the electronic noise
Development of the transducers and
electronics read out
New detector Spheres New materials
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< 10-20 Hz-1/2 on 50 Hz
1998
2001
2003
Old readout
New readout
< 10-20 Hz-1/2 on 7 Hz
WIDENING THE BAND IN EXPLORERWIDENING THE BAND IN EXPLORER
Increasing the Bandwidth of Resonant Gravitational Antennas: The Case of Explorer PRL 91, 11 (2003)
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DATA TAKINGDATA TAKING DURING 200 DURING 20044
EXPLORER NAUTILUS
3.5 ·10-19
2·10-19
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EXPLORER and NAUTILUS September 3th, 2004
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GAUSSIANITY GAUSSIANITY
EXPLORER NAUTILUS
12 hours of data on Sept 4th, 2004
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GAUSSIANITY GAUSSIANITY
EXPLORER NAUTILUS
1 day of data on July 2004
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Soglia 0.24 K1/2
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