Low Frequency Gravitational Wave

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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

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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