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Transcript
Low Frequency Gravitational
Wave Interferometric Detectors
Riccardo DeSalvo
GWADW 2002 Isola d’Elba
24th of May 2002
Is it important to build a LF-GWID ?
2
Is it important to build a LF-GWID ?
Signal to Noise ratio at 10 kpc
2000.09.04
10
2001.06.02
2
10
0
2
4
6
8
10
12
Mass (Msolar)
14
16
183
20
Technical reason Narrowing canyons
advanced LIGO
advanced LIGO 1/3 TN
advanced LIGO 3 TN
canyons
Any improvement
of thermal noise
narrows the
sensitivity canyon
Sensitivity
10-21
10-22
In these specific conditions
we can
10-23
take advantage only
of another or magnitude
of thermal noise before
the canyon closes
10-24
1
10
100
4
1000
5 10
frequency [Hz]
Shifting the canyons
advanced LIGO
advanced LIGO *10 power
advanced LIGO *.01 power 1/3 TN
canyons
To efficiently
cover a large
frequency span
it is necessary
to build
dedicated
Interferometers
each optimized
at various
frequency ranges
sensitivity
10-21
10-22
10-23
10-24
1
10
100
1000
104
frequency [Hz] 6
Reasons for a Low Frequency
Gravitational Wave Interferometic Detector
• Need to implement twin interferometers in the same
vacuum enclosure
• Complementary in frequency range
• Separately cover the high and low frequency range
• at LF not having power limitations, fused silica is
probably better than sapphire
7
Comparing the canyon bottoms
• DifferentTN
slope of
• Sapphire
Best at high
frequency
Also needed to
dissipate
high power
• and
• Fused Silica
Best at low
frequency
8
Kenji Numata
Annealing
seems
to expose
the plunge
to zero
dissipation
at zero
frequency
9
Let me
cheat for a moment
1000 Hz
Surface and
Coating losses?
Bottom of canyon?
100 Hz
10-9
10-10
10
Ingredients for LF-GWID
• 1
• 2
Seismic Attenuation
Control schemes
• 3
Mirror suspensions (today’s focus)
• 4
Mirrors
– A
– B
• 5
Substrates
Coatings
Optical layout
OK
OK
probably OK
remains to be seen
low power, will find solutions
11
Next prioriry towards a LF-GWID
• The stumbling block for a
• Low Frequency Gravitational Wave
Interferometer is
• Suspension Thermal Noise
12
This is the 1st enemy
This is the 2nd enemy
13
3 Suspension thermal noise
•
Main Argument of presentation
–
Glassy metal flex joints
–
An alternative to fused silica at low
frequency?
14
Suspension thermal noise
• Cryogenics, a tough but in the long term almost
sure bet
• If we can reach the bottom of the valley at room
temperature, why bother?
• Is there an suspension alternative
at room temperature and low frequency?
• Glassy metal flex joints
– Analyze metal vs. fused silica
15
Triple Pendulum: Thermal Noise
Factor
threeimprovement
improvement
Factor
of of
three
steel
wires
overover
steel
wires
reported for GEO
reported for GEO
by Norna Robertson.
by Norna
Robertson.
Progress limited by
Intrinsic
limitations
intrinsic
limitations
16
Alternative Suspension Solutions
metallic flex joints
• Metallic Flex joints have been evaluated in the
past for mirror suspensions (D. Blair et al.)
• Metals start disadvantaged with respect with
glasses because of lower intrinsic Q-factors
(<10,000 for metals).
• Flex joint have an edge because they allow
fabrication of ribbons with large aspect ratios =>
large pendulum dilution factors
• Metals are stronger
17
Advantages of
Glassy Metals
• Like metals easy to shape and braze: allow
advanced engineering and mechanical geometries.
• Naturally produced in thin films or ribbons.
• Not fragile (no water problem, thin ribbons)
•
•
•
18
SiO2 +H2O scissor effect
• SiO2 + H2O = 2 SiO-OH
• scissor effect
H
2
1
H
O
H
H
H
3
H
H
O
O
H
O
Si
Si
O
O
Si
Si
Si
Si
Si
O
O
Si
Si
O
Si
Si
Si
Si
O
O
O
O
Si
O
O
O
O
O
Si
Si
O
O
Si
O
Si
O
O
Si
Si
O
O
O
Si
Si
O
Si
O
O
Si
O
O
O
Si
Si
Si
O
Si
Si
O
H
O
O
Si
O
O
O
Si
Si
Si
Si
Si
O
O
O
Si
H
O
Si
Si
Si
Si
Si
Si
O
O
O
O
O
Si
Si
Si
Si
Si
O
O
Si
O
O
O
O
O
O
Si
H
Si
Si
Si
O
O
O
O
Si
O
O
H
Si
Si
O
O
Si
Si
O
O
O
O
O
19
An additional advantage
Glassy Metals
• Like metals easy to shape and braze: allow
advanced engineering and mechanical
geometries.
• Naturally produced in thin films or ribbons.
• Not fragile (no water problem)
• Allow loads of 4, 5 or even 6 GPa!!!
• (Best steel limit at 1.8 Gpa, typical fused silica 0.7 GPa)
• Very large elasticity limit (2%)
• Some metallic glasses have low internal Q-factors
but refractory metal glasses have large Q-factors
20
A pitfall
Hydrogen flipping losses
= Metal
Atom
= Hydrogen
location
Hydrogen atom flip-flop
with changing stresses
Also Q-factor is a steep
function of ratio of
melting/room temperature
21
Which Glassy Metals are promising
• Glassy metals can be manufactured
– Starting from many metals, recipe:
– Mix two close relative metals
– Molybdenum + Ruthenium
– Add Boron to frustrate the formation of
crystalline structures
– Cool rapidly
22
Which Glassy Metals are promising
• There is no qualitative difference between
• Quartz
/ Fused Silica and
• Crystalline metals/ Glassy metals
• Crystallization time
– Hours
for Fused Silica
– Seconds for Glassy Metals
23
Which Glassy Metals are promising
• Molybdenum
Ruthenium Boron
do not absorb hydrogen
and have
very high melting points
(similar or higher than Fused Silica)
24
Melting points
Element
Melting Point
( C)
Mo
2617
Glass
Melting Point
( C)
Ru
2310
MoRuB
1400-1450
B
2300
WReSiB
1600-1700
W
3410
Re
1966
Si
1410
0
0
25
Which Glassy Metals are promising
• In metallic glasses the Mo-Ru bond play
same role as the Si-O bond in Fused Silica,
both in determining the
• melting temperature the
• dissipation processes and the
• damage processes
26
Why Glassy Metals are promising
• Selected Glassy metals have high Q-factors
• But intrinsic Q factor is less important
because of the much more advantageous
possible geometries
27
Estimated MoRuB glass properties
•
•
•
•
•
•
•
•
Mo49Ru33B18 in atomic percent.
density,
9.5 g/cc
heat conductivity,
10 Watts/m-K
heat capacitance,
30 J/mole-K
linear thermal expansion coeff., 5-6 x 10-6 (K-1)
elastic modulus,
250 GPa
Poisson modulus,
0.36-0.38
breaking point
5 GPa
(not fragile, loadable to
>
4GPa)
28
• - These numbers should be accurate to +/- ~20%
Thermal noise of MoRuB flex joints
Glassy metal Q=104, Fused SiO2 dumb bell shaped fiber Q=8.4*108,
10*3000 = 30,000 mm2,
357 mm diameter, 100,000 mm2, 29
60 Kg mirror,
40 Kg mirror
What’s the development program
• Make several samples of different compositions
• Measure physical properties
–
–
–
–
–
–
Yield point,
Elastic constant
Poisson ratio
Thermal capacity
Thermal conductivity
Thermal expansion coefficient . . . . . . .
• Measure reed (diving board) Q-factors of
samples
30
What else to do
• Demonstrate feasibility of fabrication of
suspension structures
• Demonstrate feasibility of attachments to
mirrors without significant loss of
mirror Q-factor
• Test suspension Q-factors (>108) with
macroscopic mirrors
31
What is being done?
• Make several samples of different compositions
• Samples are made in Caltech Metallurgy
department (splat cooling)
32
R.F. levitation and
What is being done?
melting coil
Pulsed Copper anvils
33
34
35
36
37
38
M oRuB X-ray Patte rn
2000
Intensity
1500
1000
500
0
500
1000
1500
2000
2500
Channel Number
3000
3500
4000
39
What does splat cooling produce?
• The end product is a disk
– 50 mm thick,
– 15 mm in diameter
• The surface copies the (electropolished)
anvil’s surface to optical accuracy
• Only 3*6 mm platelets are required
40
What is being done?
• Measure physical properties
–
–
–
–
Yield point,
Elastic constant
Poisson ratio
Hysteresis
– Thermal capacity
– Thermal conductivity
– diving board Q-factors
41
What is being done?
Vit_1 Cryostat Measurement (08/04/2002)
9
Conductiv ity (W/K-m)
8
7
6
5
4
3
2
1
0
0
50
2K to 400K
10 0
15 0
20 0
25 0
Te mperature (K)
400K to 2K
30 0
35 0
40 0
2K to 400K
42
Measure reed Q-factors
• Reed
mounted on an
isolation stack
to isolate it from
cryostat
dissipation.
• Optical lever
readout
of ringdown
•Electrostatic
excitation
43
Measure reed Q-factors
Empty Cryo puck case,
periscope housing
Test reed on
Q-factor probe on puck
44
What to be done next?
• Need to Demonstrate feasibility
• of employing Glassy Metals to fabricate
• mirror suspensions with record Q-factor
45
What to be done next?
• Ingredients
– Suspension rigid structure carved by EDM
– Glassy metal Flex joints brazed to the rigid
structure
– Flex joint structure brazed to a wire
– Hook bonded to a ledge in the mirror
46
Fabricate the Flex Joint
16 mm
• EDM carve half of the Flex Joint
structure out of a single piece of
material
• The Flex Joint structure will be
finished at the very end of the
process by cutting the dashed lines
• All the surfaces on which to braze
the flex joint are aligned by birth!
47
Fabricating the
Flex Joint
thinning it from 50 to 10 mm
by through-mask
electrochemical
micromachining (IBM patent)
50 mm 10 mm 50 mm
• The Flex Joint
Is positioned by a
”Cavalier”,
with a slot to house the
thin part of flex joint
48
Fabricate the Flex Joint
• The flex joint structure, is
now provided with the
glassy metal
suspension wire
• The thin flex joints, are still
imprisoned by the cavaliers
both are brazed together by
the baking process
• After brazing the ears of the
cavaliers are EDM chopped
off before separating the
structure from its mother
49
plate
Fabricate the Flex Joint
• The finished
flex joint is
finally
ready for
attachment
to the
mirror’s
ledges
50
Fabricate the Flex Joint
• The mating surfaces of
the flex joint and of the
mirror’s ledge are
indium coated to
provide an
excess-noise-free
connection
51
Why using ledges
• The use of ledges and low temperature
brazing eliminated all shear efforts
• Can be assembled and disassembled by
simply warming up the indium
• Need to Demonstrate feasibility of
attachments to mirrors without significant
loss of mirror Q-factor
52
What is being done?
500 Kg mass
Supporting
10 Kg mirror
Observe pitch
mode
53