NOISE IN RESONANT BARS
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NOISE IN RESONANT BARS. Massimo Visco for ROG Collaboration CNR - Istituto di Fisica dello Spazio Interplanetario - Roma INFN – Sezione di Roma2. NOISE IN RESONANT DETECTORS. Matched Filtering. Thermal noise. Seismic noise. Low and ultralow temperature. Mechanical filters. Mechanical

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NOISE IN RESONANT BARS

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Noise in resonant bars

NOISE IN RESONANT BARS

Massimo Visco for ROG Collaboration

CNR - Istituto di Fisica dello Spazio Interplanetario- Roma

INFN – Sezione di Roma2


Noise in resonant detectors

NOISE IN RESONANT DETECTORS

Matched

Filtering

Thermal noise

Seismic noise

Low and ultralow

temperature

Mechanical filters

Mechanical

vibration

Electrical

signal

GW

TRANSDUCER

AMPLIFIER

DATA

dL

Cosmic ray

noise

Electronic noise

Veto

Low noise amplifier

(SQUID)


Noise in resonant bars

CROSSSECTION

·The cross section is sharply peaked at the resonant frequency

/0

Sound

speed

Resonance

curve

Antenna

mass

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


Noise in resonant bars

First stage

Second stage


Noise in resonant bars

  • Vertical direction

  • Horizontal direction


Auriga suspensions

AURIGA SUSPENSIONS

LHe4 vessel

Al2081 holder

Electronics wiring support

Main Attenuator

Thermal Shield

Compression Spring

Transducer


The construction of a cryogenic suspensions column

The construction of a cryogenic suspensions column


Noise in resonant bars

Columns modes up 180 Hz

Holder modes

Titanium springs

1E-9

No lines

690-1250 Hz

1E-10

1E-11

displacement (m)

1E-12

1E-13

1E-14

1E-15

500

1000

1500

2000

m/Hz1/2

frequency (Hz)

Accelerometerover the holder

at 600 Hz attenuation > 140dB (theoretical 186 dB)

C shaped springs modes

Accelerometer bottom of the column

Electronic noise of the accelerometer

m/Hz1/2


Noise in resonant bars

CRIOSTATO DI NAUTILUS

Cosmic ray

detector

Cosmicray

detector

SQUID

electronics

Cylindricalbar

Rotating

platform

Dilution

refrigerator

SQUID

amplifier

Cryostat

Transducer


Dilution refrigerator

DILUTION REFRIGERATOR

  • NAUTILUS and AURIGA bars are the largest mass ever cooled below 1K (145 mK)


Noise in resonant bars

3He out

3He

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.

4He

Mixing chamber


Noise in resonant bars

Thermal contacts and acoustic isolation


Effect of cosmic rays on a resonant detector

EFFECT OF COSMIC RAYS ON A RESONANT DETECTOR

o

zo

lo

2 R

L

Grüneisen coefficient

Energy lost

Calculation for Nautilus

sound velocity

density

The longitudinal mode of vibration of the antenna is excited by the thermal expansion due to the energy lost by the particles


Noise in resonant bars

11.5 mK

  • The first analysis confirmed the calculation made by several authors.

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.

threshold

P.Astone et al.: ”Energetic Cosmic Rays observed by the resonant gravitational wave detector NAUTILUS" , Phys. Letters B 499, Feb 2001 16-22

time (s)


Noise in resonant bars

T<1K

Event rate (day-1)


Noise in resonant bars

T> 1K


Noise in resonant bars

COSMIC RAY INTERACTION

WITH NAUTILUS

72 streamer chambers (6x6)m

Antenna

30 streamer chambers (2.5x6)m


Noise in resonant bars

Thermal noise

SF = MkTwr/Q

Electronic noise

Vn; In Tn=√Vn2In2 /k

The mechanical oscillator

Mass M

Speed of sound vs

Temperature T

Quality factor Q

Res. frequency fr

The amplifier

Noise temperature Tn

The transducer

Efficiency 


New amplifier

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


Noise in resonant bars

Trento

(2 stage)

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


How the different sources of noise contribute to the overall sensivity

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


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 .

NOISE CONTRIBUTION IN BAR DETECTORS

SNR

Narrow-band Noise

Signal


Noise in resonant bars

·When the wide-band noise is not negligible the bandwidth of the detector depends on the ratio between wide and narrow band noise ():

SNR

Signal

wide-band Noise

Narrow-band Noise


Sensitivity of bar detectors

SENSITIVITY OF BAR DETECTORS

  • The sensitivity of a detector is usually given in terms of the noise spectral density referred to the input of the antenna

Sh (1/Hz)

  • 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.


Noise in resonant bars

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:

Development of the transducers and electronics read out

  • Increase the coupling

  • Reduce the electronic noise


Widening the band in explorer

WIDENING THE BAND IN EXPLORER

< 10-20 Hz-1/2 on 7 Hz

Old readout

1998

< 10-20 Hz-1/2 on 50 Hz

2001

New readout

2003

Increasing the Bandwidth of Resonant Gravitational Antennas: The Case of ExplorerPRL 91, 11 (2003)


Data taking during 200 4

DATA TAKING DURING 2004

NAUTILUS

EXPLORER

3.5 ·10-19

2·10-19


Noise in resonant bars

EXPLORER and NAUTILUS September 3th, 2004


Gaussianity

GAUSSIANITY

NAUTILUS

EXPLORER

12 hours of data on Sept 4th, 2004


Gaussianity1

GAUSSIANITY

NAUTILUS

EXPLORER

1 day of data on July 2004


Noise in resonant bars

Soglia 0.24 K1/2


Noise in resonant bars

END


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