Transcript PERFORMANCE OF RESONANT BAR DETECTORS

NOISE IN RESONANT BARS
Massimo Visco for ROG Collaboration
CNR - Istituto di Fisica dello Spazio Interplanetario- Roma
INFN – Sezione di Roma2
Hannover, 24 September 2004
NOISE IN RESONANT DETECTORS
GW
Mechanical
vibration
Electrical
signal
TRANSDUCER
AMPLIFIER
DATA

dL
Seismic noise
S( f )ei2ft0
K( f ) 
N( f )
Thermal noise
Mechanical filters Low and ultralow
temperature
Cosmic ray
noise
Veto
Matched
Filtering
Electronic noise
Low noise amplifier
(SQUID)
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CROSS SECTION
 The cross section is sharply peaked at the resonant frequency
0
 ( )  cos t M vs2
Q
 
(  0 )   0 
Q
2
Antenna
mass
Sound
speed
/0
Resonance
curve
2
sin 4  cos2 (2 )
Direction
Polarization
 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
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First stage
Second stage
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• Horizontal direction
20
20
10
10
0
-10
1
stage
-20
-30
-40
-50
-60
horizontal attenuation (dB)
1
stage
vertical attenuation (dB)
• Vertical direction
0
-10
-20
-30
-40
-50
-60
-70
10
100
1000
-70
10000
10
frequency (Hz)
100
1000
10000
frequency (Hz)
20
2
stage
vertical attenuation (dB)
10
0
2
stage
-10
-20
-30
-40
-50
horizontal attenuation (dB)
20
10
0
-10
-20
-30
-40
-50
-60
-60
-70
-70
10
100
1000
frequency (Hz)
10000
10
100
1000
10000
frequency (Hz)
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AURIGA SUSPENSIONS
LHe4
vessel
Al2081 holder
Electronics
wiring support
Thermal Shield
Main
Attenuator
Compression
Spring
Transducer
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The construction of a cryogenic suspensions column
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at 600 Hz attenuation > 140dB
(theoretical 186 dB)
Columns
modes up
180 Hz
Titanium
1E-9
springs
Holder modes
C shaped
springs
modes
No lines
690-1250 Hz
1E-10
displacement (m)
Accelerometer over the holder
1E-11
1E-12
1E-13
Accelerometer bottom
of the column
1E-14
1E-15
m/Hz1/2
m/Hz1/2
500
1000
frequency (Hz)
1500
2000
Electronic noise
of the
accelerometer
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CRIOSTATO DI NAUTILUS
Cosmic ray
detector
Cylindrical bar
Cosmic ray
detector
SQUID
electronics
Rotating
platform
SQUID
amplifier
Dilution
refrigerator
Cryostat
Transducer
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DILUTION REFRIGERATOR
1K Pot
Thermal contact
Still
Heat exchanger I
Copper shields
Heat exchanger II
Mixing chamber
Antenna
Copper cable
• NAUTILUS
and AURIGA bars
are the largest mass ever cooled
below 1K (145 mK)
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3He-4He
Dilution Refrigerator
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.
3He
out
3He
4He

Q
Mixing chamber
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Thermal contacts and acoustic isolation
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EFFECT OF COSMIC RAYS ON A RESONANT
DETECTOR
Grüneisen
coefficient
Energy
lost
2
4  2  dW 2    zo  sin(  lo cos( o ) / 2 L) 
9 2  K 


E
sin

7
.
64
x
10
W f 

  



2
9  L v  dx    L   R cos( o ) / L 
 GeV 2 
density
Calculation for
Nautilus
sound
velocity
o
zo
lo
2R
The longitudinal mode of
vibration of the antenna is excited
by the thermal expansion due to
the energy lost by the particles
L
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• The first analysis
confirmed the calculation
made by several authors.
11.5 mK
P.Astone et al.: “Cosmic rays observed by
the Resonant Gravitational wave detector
Nautilus" Physical Review Letter, 84,
(2000)14-17
Average
58 K
87 TeV
(K)
(x 5000)
• 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
threshold
time (s)
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T<1K
100
Solo T < 1 Kelvin
10
Event rate (day-1)
Eventi /giorno distrib integrale
predizioni
Ev/Giorno Nauti lus 98
Nautilus 2000 T <1 K
1
0.1
0.01
0.001
0.01
0.1
1
10
Sqrt(Kelvin)
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Explorer ev/giorno tutto 2003
predizioni
EXPLORER 2002 >600 P M2
Nautilus 2003 ev giorno
Nautilus 2000-2001 ev/giorno
T> 1K
Eventi /giorno distrib integrale
100
Solo T > 1 Kelvin
10
1
0.1
0.01
0.001
0.001
0.01
0.1
Sqrt(Kelvin)
1
10
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COSMIC RAY INTERACTION
WITH NAUTILUS
Mode energy events/day events/day events/day events/day events/day
threshold (K) (muons)
(hadron)
(EAS) (multi had.)
(total)
10-2
10-3
10-4
10-5
10-6
10-7
0.002
0.18
1.2
12.7
155
1540
0.035
0.56
6.2
55.7
463
3310
0.04
0.24
1.3
7
35
137
0.18
1.2
3.7
5.5
0.18
2.18
12.4
80.9
653
4987
72 streamer chambers (6x6)m
Antenna
30 streamer chambers (2.5x6)m
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Thermal noise
Electronic noise
SF = MkTr/Q
The mechanical
oscillator
Mass M
Speed of sound vs
Temperature T
Quality factor Q
Res. frequency fr
Vn; In
Tn=√Vn2In2 /k
The transducer
The amplifier
Efficiency 
Noise temperature Tn
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NEW AMPLIFIER
• For the read-out of resonant detectors SQUID amplifiers
were widely used, to avoid the second stage noise a double
squid amplifier is required
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Trento
(2 stage)
• An alternative possible read-out is one based on a Back
Action Evading scheme
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HOW THE DIFFERENT SOURCES OF NOISE
CONTRIBUTE TO THE OVERALL
SENSIVITY?
• There are two intrinsic sources of
noise that cannot be avoided
- Thermal noise
- Electronic noise
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NOISE CONTRIBUTION IN BAR DETECTORS
• The signal and the narrow-band noise have similar
shape. If we consider only narrow band- noise the
bandwidth is infinite .
SNR
4
1 10
3
1 10
1 00
10
1
0 .1
0 .0 1
3
1 10
4
1 10
5
1 10
6
1 10
7
1 10
0 .4
Narrow-band
Noise
Signal
0 .6
0 .8
1
1 .2
1 .4
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
When the wide-band noise is not negligible the bandwidth
of the detector depends on the ratio between wide and
narrow band noise ():
0
Q 

Narrow-band
Noise
SNR
4
1 10
3
1 10
1 00
10
1
0 .1
0 .0 1
3
1 10
4
1 10
5
1 10
6
1 10
7
1 10
0 .4
Signal
0 .6
0 .8
1
1 .2
1 .4
wide-band
Noise
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Sh (1/Hz)
SENSITIVITY OF BAR DETECTORS
f 

Tn
T
~
h e
MQ
• The sensitivity of a
detector is usually given
in terms of the noise
spectral density referred
to the input of the
antenna
~
h ( fr )
hmin 
 g f
~
h
• 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.
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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
New detector
Spheres
New materials
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
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WIDENING THE BAND IN EXPLORER
< 10-20 Hz-1/2 on 7 Hz
1998
2001
Old
readout
< 10-20 Hz-1/2 on 50 Hz
New
readout
2003
Increasing the Bandwidth of Resonant Gravitational Antennas: The Case of Explorer PRL 91, 11 (2003)
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DATA TAKING DURING 2004
EXPLORER
NAUTILUS
3.5 ·10-19
2·10-19
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EXPLORER and NAUTILUS
September 3th, 2004
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GAUSSIANITY
EXPLORER
NAUTILUS
12 hours of data on Sept 4th, 2004
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GAUSSIANITY
EXPLORER
NAUTILUS
1 day of data on July 2004
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Soglia 0.24 K1/2
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END
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