piero rapagnani i.n.f.n. sezione di roma

April 27th, 2006April 27th, 2006 Piero Rapagnani – INFN RomaPiero Rapagnani – INFN Roma

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Cryogenic payloads and cooling systems Cryogenic payloads and cooling systems (towards a third generation interferometer)(towards a third generation interferometer)

part I:part I: An Interferometer at An Interferometer at Cryogenic TemperaturesCryogenic Temperatures

Piero RapagnaniPiero RapagnaniI.N.F.N. Sezione di Roma I.N.F.N. Sezione di Roma


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Test masses and suspensions thermal noise reduces at low temperature:Test masses and suspensions thermal noise reduces at low temperature:

Thermoelastic noise both of the mirror substrates and coatings decrease:Thermoelastic noise both of the mirror substrates and coatings decrease:

Thermal expansion rate Thermal expansion rate decreases at low temperature; decreases at low temperature;

Mechanical Q of some materials increases at low temperatureMechanical Q of some materials increases at low temperature

@ @ intint

Thermal lensing:Thermal lensing: Thermal conductivity increases and consequently reduces thermal Thermal conductivity increases and consequently reduces thermal

gradients on the coating;gradients on the coating; Refraction index variation with temperature is very small at low Refraction index variation with temperature is very small at low

temperature; temperature;

Why cool the mirrors?Why cool the mirrors?

Tx >∝< 2

22 Tx >∝<

QT

x >∝< 2


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R&D on CryogenicsR&D on Cryogenics

1) Study of the refrigeration system

- noise

- refrigeration power

2) Suspension compatibility: thermal conduction and acoustic quality factor Q measurements

3) Sensors at low temperatures

- accelerometers and position sensing devices

- actuators

Liquid heliumRefrigeratorsHybrid system


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Issues to cool the mirrorsIssues to cool the mirrors Refrigeration system:Refrigeration system:

• The The injected mechanical noise must be negligibleinjected mechanical noise must be negligible, the , the sensitivity must be preserved:sensitivity must be preserved:

Good mechanical isolation between the Good mechanical isolation between the mirror mirror and the cooling system; and the cooling system;

• Cooling time of the mirror as low as possibleCooling time of the mirror as low as possible::

Good thermal couplings;Good thermal couplings;

High refrigeration power;High refrigeration power; Suspension system compatible with good mechanical and Suspension system compatible with good mechanical and

thermal couplings: thermal couplings:

• Thermal conductivities change with temperature;Thermal conductivities change with temperature;• Mechanical quality factor Q;Mechanical quality factor Q;


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Cryogenic fluids and G.W. DetectorsCryogenic fluids and G.W. Detectors

The first cryogenic antenna in the world 1974-1980: The first cryogenic antenna in the world 1974-1980: M=20 kg, T =4 K , M=20 kg, T =4 K , ~ 5 kHz ~ 5 kHz

No excess noise


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The second cryogenic antenna of the Rome group The second cryogenic antenna of the Rome group -1978: -1978: M~ 400 kg, T =4 K , M~ 400 kg, T =4 K , ~ 1.8 kHz ~ 1.8 kHz

Excess noise in the first phase of operation:Due to suspension system!!


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Advantage of the Advantage of the superfluid liquid superfluid liquid Helium:Helium:

the the transition transition

Data from the AntennaEXPLORERinstalled at CERN

He phase transition to superfluid


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• The current technique to cool down a Resonant Antenna requires “Heavy Work” and several weeks• Detector duty cycle: less than 1 month.

VIRGO

• For an interferometric antenna 6 masses to be cooled. • To preserve the duty cycle this “heavy work” must be done in parallel.....

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.


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QuickTime™ and aTIFF (LZW) decompressor


In a BIG Laboratory,large Cryogenic Facilities are possible

The example of LHC at CERN:

Technologies are available, but are VERY expensive and require extensive manpower

The Cryogenic Distribution Line (QRL) for the LHC (Large Hadron Collider). Each of the eight ~3.2 km QRL sectors is feeding Helium at different temperatures and pressures to the local cooling loops of the strings of superconducting magnets operating in superfluid helium below 2 K. With an overall length of 25.8 km the QRL has a very critical cost to performance ratio.


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An alternative way to cool down without liquid helium: An alternative way to cool down without liquid helium: the new generation of Cryocoolersthe new generation of Cryocoolers

First stage

Second stage

Suitable for applications that require efficient operation:

No moving parts in cold head. Minimal vibration, low acoustic noise, reliability.

High efficiency: 2 to 3 times higher efficiency than GM cryocoolers for loads temperatures between 55 and 120 K.

• A Pulse Tube Refrigerator (PTR) or "G-M style" pulse tube cryocooler, is a variant of a Gifford-McMahon (GM) cryocooler.

• PTR operate at low frequencies, typically <5 Hz.

• Used a conventional oil-flooded G-M compressor and a valve set near the cold head to convert the continuous flow of helium to a low frequency pressure wave.


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A possible solutionA possible solutionPassive vibrational Passive vibrational isolation system for isolation system for the heat linkthe heat link

Long heat linkLong heat link Part of the Part of the

refrigerating power refrigerating power absorbed by the absorbed by the isolatorsisolators

Attenuation of the Attenuation of the refrigerating powerrefrigerating power


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Our solutionOur solution

Active vibration isolation system for the heat link

Shorter heat linkShorter heat link Refrigerating Refrigerating

power preservedpower preserved


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Q from refrigerator

Q from laser beam

Mirror Reaction Mass: Thermal Shield at ~ 4K

Marionetta Reaction Mass: Thermal Shield at ~ 4K

High Efficiency Thermal Links

Vacuum Chamber and Cryostat Thermal Shields

Silicon Monolithic Wire


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Q from refrigerator

Q from laser beam

Mirror Reaction Mass: Thermal Shield at ~ 4K

Marionetta Reaction Mass: Thermal Shield at ~ 4K




Rough Estimates give Tmirror ~ 10 K


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Q from Superfluid Helium Reservoir

Q from laser beam

Mirror Reaction Mass: Thermal Shield at ~ 1.5 K

Marionetta Reaction Mass: Thermal Shield at ~ 1.5 K




A hybrid system usingSuperfluid Helium could

allow to reach T ~ 1.5 K


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Thermal Links:Many Materials andComposites available

Thermal behaviorat low temperaturesmust be tested


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The short/medium term future:The short/medium term future:The Cryogenic Suspension Test The Cryogenic Suspension Test

FacilityFacilityStill non investigated Problems:

Thermal link (T ~ 4 K)

Cryogenic (T~ 50 K)Suspension Elements

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