Low Frequency Gravitational Wave Interferometric Detectors: 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 ?: Is it important to build a LF-GWID ?
Is it important to build a LF-GWID ?: Is it important to build a LF-GWID ?
Reasons for a Low FrequencyGravitational Wave Interferometic Detector: Reasons for a Low Frequency Gravitational Wave Interferometic Detector Also some technical reasons:
As the mirror thermal floor is pushed low the canyon between
radiation pressure noise and
shot noise walls
becomes narrower
Technical reason Narrowing canyons: Technical reason Narrowing canyons Any improvement
of thermal noise
narrows the
sensitivity canyon
In these specific conditions
we can
take advantage only
of another or magnitude
of thermal noise before
the canyon closes
Shifting the canyons: Shifting the canyons To efficiently
cover a large
frequency span
it is necessary
to build
dedicated
Interferometers
each optimized
at various
frequency ranges
Reasons for a Low FrequencyGravitational Wave Interferometic Detector: 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
Slide8: 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
Slide9: Annealing
seems
to expose
the plunge
to zero
dissipation
at zero
frequency Kenji Numata
Slide10: Surface and
Coating losses? Let me cheat for a moment 10-9 10-10 1000 Hz 100 Hz Bottom of canyon?
Ingredients for LF-GWID: Ingredients for LF-GWID 1 Seismic Attenuation OK
2 Control schemes OK
3 Mirror suspensions (today’s focus)
4 Mirrors
A Substrates probably OK
B Coatings remains to be seen
5 Optical layout low power, will find solutions
Next prioriry towards a LF-GWID: Next prioriry towards a LF-GWID The stumbling block for a
Low Frequency Gravitational Wave Interferometer is
Suspension Thermal Noise
Slide13: This is the 1st enemy
This is the 2nd enemy
3 Suspension thermal noise: 3 Suspension thermal noise Main Argument of presentation
Glassy metal flex joints
An alternative to fused silica at low frequency?
Suspension thermal noise: 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
Slide16: Factor of three improvement
over steel wires
reported for GEO
by Norna Robertson.
Intrinsic limitations Factor of three improvement
over steel wires
reported for GEO
by Norna Robertson.
Progress limited by
intrinsic limitations
Alternative Suspension Solutionsmetallic flex joints: 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 (andlt;10,000 for metals).
Flex joint have an edge because they allow fabrication of ribbons with large aspect ratios =andgt; large pendulum dilution factors
Metals are stronger
Advantages of Glassy Metals: 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)
SiO2 +H2O scissor effect: SiO2 +H2O scissor effect SiO2 + H2O = 2 SiO-OH
scissor effect
An additional advantage Glassy Metals: 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
A pitfallHydrogen flipping losses: A pitfall Hydrogen flipping losses Hydrogen atom flip-flop with changing stresses Also Q-factor is a steep function of ratio of melting/room temperature
Which Glassy Metals are promising: 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
Which Glassy Metals are promising: 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
Which Glassy Metals are promising: Which Glassy Metals are promising Molybdenum Ruthenium Boron
do not absorb hydrogen
and have
very high melting points
(similar or higher than Fused Silica)
Melting points: Melting points
Which Glassy Metals are promising: 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
Why Glassy Metals are promising: 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
Estimated MoRuB glass properties: 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 andgt; 4GPa)
- These numbers should be accurate to +/- ~20%
Thermal noise of MoRuB flex joints: 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,
60 Kg mirror, 40 Kg mirror
What’s the development program: 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
Slide31: Demonstrate feasibility of fabrication of suspension structures
Demonstrate feasibility of attachments to mirrors without significant loss of mirror Q-factor
Test suspension Q-factors (andgt;108) with macroscopic mirrors What else to do
What is being done?: What is being done? Make several samples of different compositions
Samples are made in Caltech Metallurgy department (splat cooling)
What is being done?: What is being done? R.F. levitation and melting coil
Pulsed Copper anvils
Slide34:
Slide35:
Slide36:
Slide37:
Slide38:
Slide39:
What does splat cooling produce?: 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
What is being done?: What is being done? Measure physical properties
Yield point,
Elastic constant
Poisson ratio
Hysteresis
Thermal capacity
Thermal conductivity
diving board Q-factors
What is being done?: What is being done?
Measure reed Q-factors: Measure reed Q-factors Reed mounted on an isolation stack to isolate it from cryostat dissipation.
Optical lever readout of ringdown Electrostatic excitation
Slide44: Measure reed Q-factors Empty Cryo puck case,
periscope housing
Test reed on
Q-factor probe on puck
What to be done next?: What to be done next? Need to Demonstrate feasibility
of employing Glassy Metals to fabricate
mirror suspensions with record Q-factor
What to be done next?: 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
Fabricate the Flex Joint: Fabricate the Flex Joint 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! 16 mm
Fabricating the Flex Joint: Fabricating the Flex Joint The Flex Joint
Is positioned by a 'Cavalier',
with a slot to house the
thin part of flex joint
thinning it from 50 to 10 mm by through-mask electrochemical micromachining (IBM patent) 50 mm 10 mm 50 mm
Fabricate the Flex Joint: 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 plate
Fabricate the Flex Joint: The finished flex joint is finally ready for attachment to the mirror’s ledges Fabricate the Flex Joint
Fabricate the Flex Joint: 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
Why using ledges: 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
What is being done?: What is being done? 500 Kg mass
Supporting
10 Kg mirror
Observe pitch mode