Silica Research in Glasgow Gianpietro Cagnoli – IGR - University of Glasgow GEO Collaboration...
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Transcript of Silica Research in Glasgow Gianpietro Cagnoli – IGR - University of Glasgow GEO Collaboration...
Silica Research in Glasgow
Gianpietro Cagnoli – IGR - University of Glasgow
GEO CollaborationGinzton Lab, Stanford
Caltech
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 2
Summary
Silica suspensions in GEO600
Direct Measurement of Thermal
Noise
Coating Losses
Non-Linear Thermoelastic Effect
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 3
Silica suspensions in GEO600GEO600 Collaboration
Two monolithic silica suspensions have been installed in GEO600 (middle of June)
GEO600 is the first interferometer to use such suspension to reduce thermal noise
Some numbers:fibres length = 285 mmvertical freq. ~ 16 Hzmirror mass = 5.6 kg
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 4
Silica suspensions in GEO600
Features: 4 fibres welded on
“ears” 2 silicate bonded ears
each mass Selective damping of
violin modes with teflon coating on fibres
Masses are hold in a rigid frame during the welding and transportation inside the tank
Once the stage is suspended the holding frame becomes a catcher
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 5
Silica suspensions in GEO600
Coating Cutting
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 6
Silica suspensions in GEO600
Welding (test)
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 7
Direct measurement of thermal noiseGEO600 Collaboration
During the last year the 10m interferometer in Glasgow have been upgraded
A sensitivity limit lower than 10 –18 m/Hz ½ has been achieved above 500 Hz (blue curve at right)
Shot noise = 2·10 –19 m/Hz ½
Damping of the internal modes of one mass was increased by spreading 3 strips of grease on the barrel and noise was again measured (red curve)
1E-19
1E-18
1E-17
1E-16
1E-15
1E-14
100 600 1100 1600
Frequency [Hz]
Dis
pla
ce
me
nt
SD
[m
/sq
rt(H
z)]
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 8
1E-19
1E-18
1E-17
1E-16
1E-15
1E-14
100 600 1100 1600
Frequency [Hz]
Dis
pla
ce
me
nt
SD
[m
/sq
rt(H
z)]
Direct measurement of thermal noise
Q of several modes were measured Q ~ 1800 for greased mass Q ~ 1.2·10 5 for clean masses
Thermal noise estimation- semi-infinite mass - homogeneous structural damping (Levin Yu., Phys.Rev. D, 57 (2), 659-
663)
Results:Fluctuation-Dissipation Theorem has been verified experimentally
4 masses Q = 120000
3 masses Q = 1200001 mass Q = 1800
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 9
Coating lossesGlasgow and Stanford Collaboration
Identify and measure the coating loss from Q measurements on silica cylinders
Sample: - Corning 7980- 127 mm diameter, 100 mm length- IR coating on front faces and barrel
0.E+00
1.E-07
2.E-07
3.E-07
4.E-07
2.E+04 3.E+04 4.E+04
Frequency [Hz]
Measurements: - ring down method, 7 modes measured - 15 different sample suspensions tested
Finite elements analysis: - used for energy ratios (surface to bulk) - convergence with N. of points checked - agreement to a few % with measured frequencies
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 10
Coating losses
Two parameters model:
Cff is the front face to bulk energy
ratio
cffb C
then…another source of loss is significant
0.E+00
1.E-07
2.E-07
3.E-07
4.E-07
0.0E+00 5.0E-04 1.0E-03 1.5E-03
front face to bulk energy ratio
Cff
1st asym
1st sym
Results & comments: - all modes but 1st asymmetric are lined up - low loss measurement is not accidental - 1st symmetric mode loss too high? - but then the linear fitting is not good
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 11
Coating losses
Three parameters model:
Cb is the barrel surface to bulk energy
ratio
cbbcffb CC
0.E+00
1.E-07
2.E-07
3.E-07
4.E-07
0.E+00 1.E-07 2.E-07 3.E-07 4.E-07
theory
e
xp
eri
me
nt
1st sym
2nd asym
Results & comments: - apart for the 1st symmetric mode
(high loss) the other points are aligned- other sources of loss are currently
under investigation to justify the high value measured for the 1st symmetric mode
b = (5.8 ± 0.4)·10 –8 c = (3.8 ± 0.5)·10 –5 cb = (4.2 ± 0.3)·10 –5
From the best fit without 1st sym:
Coating losses could be a serious limit to the next generation interferometers
0.E+00
1.E-07
2.E-07
3.E-07
4.E-07
2.E+04 3.E+04 4.E+04
Frequency [Hz]
1st asym
1st sym
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 12
Asymmetrical thermal fluctuations are responsible of thermoelastic noise on silica fibres
Non-linear thermoelastic effectGlasgow and Caltech Collaboration
Loss angle:
22
1
C
TE
In linear thermoelastic effect thermal expansion coefficient transforms thermal fluctuations in strain fluctuations
= ·T
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 13
P
Non-linear thermoelastic effect
This second order effect becomes relevant due to the large longitudinal static stress o in the suspension fibre
In non-linear thermoelastic effect thermal fluctuations are transformed in strain fluctuations through the thermoelastic coefficient ·dd
Loss angle:
2
2
1
C
TE
E
T
P
SE
LPL
P
TLLL )(
11th July 20014th Edoardo Amaldi Conference on
GW, Perth, 8th – 13th July 2001 14
Non-linear thermoelastic effect
With a static stress o = 200 Mpathermal expansion is compensated and
thermoelastic noise is cancelled
An article will be submitted soon to Phys. Rev. D by Cagnoli G. and Willems P.
Some numbers for silica:
= 5.5·10 –7 K –1
= 2·10 –4 K –1
E = 72 GPa
POSITIVE !
= 0·T