noise in resonant bars

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


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 )


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


First stage

Second stage


-70

-60

-50

-40

-30

-20

-10

0

10

20

10 100 1000 10000

frequency (Hz)

ve

rtic

al a

tte

nu

ati

on

(d

B)

-70

-60

-50

-40

-30

-20

-10

0

10

20

10 100 1000 10000

frequency (Hz)

vert

ical

att

enu

atio

n (

dB

)

-70

-60

-50

-40

-30

-20

-10

0

10

20

10 100 1000 10000

frequency (Hz)

ho

rizo

nta

l att

enu

atio

n (

dB

)

-70

-60

-50

-40

-30

-20

-10

0

10

20

10 100 1000 10000

frequency (Hz)

ho

rizo

nta

l att

enu

atio

n (

dB

)

• Vertical direction • Horizontal direction

1

stage

1

stage

2

stage

2

stage


AURIGA SUSPENSIONSAURIGA SUSPENSIONS

Transducer

Electronics wiring support

LHe4 vessel

Al2081 holder

Main Attenuator

Compression Spring

Thermal Shield


The construction of a cryogenic suspensions column


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


Cosmic ray detector

Cylindrical bar

Cosmic ray detector

Rotatingplatform

SQUID electronics

SQUIDamplifier

Transducer

Cryostat

Dilution refrigerator

CRIOSTATO DI NAUTILUSCRIOSTATO DI NAUTILUS


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)


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


Thermal contacts and acoustic isolation


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


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)


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)


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


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


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


• 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


•An alternative possible read-out is one based on a Back Action Evading scheme

Trento(2 stage)


• 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?


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 .


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


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


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


< 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)


DATA TAKINGDATA TAKING DURING 200 DURING 20044

EXPLORER NAUTILUS

3.5 ·10-19

2·10-19


EXPLORER and NAUTILUS September 3th, 2004


GAUSSIANITY GAUSSIANITY

EXPLORER NAUTILUS

12 hours of data on Sept 4th, 2004


GAUSSIANITY GAUSSIANITY

EXPLORER NAUTILUS

1 day of data on July 2004


Soglia 0.24 K1/2


END

noise in resonant bars

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