STREGA WP2 - Task C3

STREGA WP2 - Task C3

Roberto Passaquieti

Dipartimento di Fisica “E. Fermi” Università di Pisa

INFN sezione di Pisa

ILIAS-GW GENERAL MEETING , Orsay 5 November 2004

ILIAS-GW General Meeting R. Passaquieti 5 November 2004 2

STREGA: WP2-C3 Task

• Task description:• to design an anti-seismic suspension system performing like a Virgo

Superattenuator and also able of removing from its payload the power absorbed from the impinging laser beam (< 1W).

– Objectives:• to assembly and test a cryo-compatible suspension system prototype,

• to install this system into a cryogenic environment,

• to investigate the extra noise from the cryogenic apparatus and to reduce it to a negligible value.

• To reach such objectives it is foreseen the merging with task C1 activities during the last 4th year of the project,

• also during the first part of the project some activities are in common between C1 and C3 task (investigation on sensors and actuators, invstigation on material properties, noise studies, simulation software, etc.)


• Up to now the C3 activities have concerned the following points:

– design and thermo-mechanical FEA of a mono-crystalline silicon payload prototype ( INFN Pisa, EGO )

– assembly of a small scale suspension system at room temperature (INFN Pisa)

– preliminary investigation on material properties at low temperature,– preliminary investigation on sensors and actuators –

– design and realization of a cryogenic test facility at the EGO site (INFN Pisa, Leiden Univ. , EGO) :

– one large cryostat capable to contain a test payload and one anti-seismic mechanical filter

– one small cryostat for devices and material properties tests,

– tests on high compliance and high thermal conductivity metal strips (INFN Pisa)

C3 Task - Main Activities


Payload Prototype• The designed payload prototype consists

of a silicon mirror (350mm diam., 100 mm thick, 22kg weight) suspended to a silicon marionette by two couples of low dissipative, monolithic silicon ribbons (30mm x 0.8 mm x 300 mm).

• Silicon peculiarity:– thermal expansion coefficient shows two zero

crossings at 123K and 17K.• Mirror displacement fluctuations driven by

thermal expansion tend to be negligible nearby these low temperature values.

• Its relatively high thermal conductivity has also the positive effect of reducing mirror thermal lensing 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300

-1x10-6

0

1x10-6

2x10-6

3x10-6

4x10-6

5x10-6

0

1000

2000

3000

4000

5000

6000

The

rmal

exp

ansi

on c

oeffi

cien

t [K

-1]

Temperature [K]

The

rmal

Con

duct

ivity

[W m

-1 K

-1]


Payload Design and Mechanical FEA

210 Hz210 Hz


Payload Thermal FEA


COLD FINGER

Very SoftJoints

Cryostat

COLD FINGER

Two alternative solutions to mirror heat extraction problemTwo alternative solutions to mirror heat extraction problem


Superattenuator Components

• Superattenuator functional blocks:• Filters

• Blades

• Magnets for anti-springs

• Dampers

• Sensors: LVDT

• Actuators: coils+magnets

• Cabling

• Motors

• Adhesives

• Start of the investigation on material cryo compatibility


Cryogenic Properties of SA Materials

• Suitable materials:• ferritic steels with 5-9 Ni• 300-series austenitic steels: 304, 304L, 316, 321, 304LN, 316LN• stable austenitic alloys: Fe-Ni-Cr-N alloys, Fe-Mn-Cr-N alloys and Inconel 908• OFHC copper and deoxidized copper• Al alloys: 6061, 6063, 1100• titanium, niobium• Invar• Kapton, mylar• quartz

• Not recommended:• martensitic steels (undergo ductile to brittle transition)• carbon steels• rubbers, plastics, Teflon

• Maraging: 18Ni (200) series tested at room temperature and 100K exhibits ductile fracture


Test of Assembled Filter at 77 K and 4.2 K

• Thermal contraction:• Thumb rule: some mm/m

contraction for metal rods between 300 and 4 K

• Problems: misalignments, increased strain

• Most contraction occurs between 300 and 77 K: significant test of assembled filter at liquid nitrogen temperature


Cryogenic Creep• Creep can be significant at cryogenic temperature Cu, Al, etc

• No validity of simple extrapolation from room temperature according to Arrhenius process with activation energy depending on temperature.

• Steel at 20 K, r>1 creep strain= (0.9-16)x10-4

• Steel at 77 K, r >1: creep strain= (7.4-30)x10-4

• Steel at 77 K, r <1: creep strain= (0.35-2.7)x10-4

• r = stress/yield strength

• Necessity of focused experimental activity


List of Investigations on Suspension Materials

• Selection of material for heat links and thermal conductivity measurement

• Definition of mechanical and thermal behavior of materials for filter components; test of an assembled filter at 77 K and at 4.2 K

• Quality factor of damping material at low temperatures, in case dampers will be used

• Dimensioning of power and signal cabling keeping into account the heat transported by conduction and the heat produced by Joule dissipation

• Test of LVDTs and accelerometers at cryogenic temperatures

• Qualification of cryogenic motors in the working conditions of VIRGO

• Test of adhesive strength and effect on quality factor of mirrors at low temperatures

• Cryogenic creep: impact on blades material and suspensions in general; long term test.

• A small cryostat is going to be insatalled in Cascina and it will allow to carry on some of these investigations.


Suspension Prototype Assembly

• A small scale suspension prototype (LIGO SAS) is going to be assembled at the Pisa INFN laboratories.

• This system is valid for both strategies.

• It has less cryogenic incompatible items (no magnets, no glue, no viton,…..) and could be used at 4 K with minor modifications

• Short term activity:– room temperature tests on

– blades

– sensors

– actuators

– thermal links

– measurement of chain TF.

• Long term activity:– replica of the tests into a cryogenic environment.


EGO Cryogenic Test Facility

• The INFN Pisa and Leiden groups are participating to the EGO CTF birth. This facility will be able to host a cryo-suspension system

• The EGO CTF will consist essentially of a large cryostat with an inner 4K chamber able to contain a test payload with one anti-seismic filter stage, and one additional small cryostat for material properties studies.

• It is placed at the mid of the West arm of the Virgo interferometer.• The large cryostat will be suspended over a pit in the ground floor (length=13.8

m, width=5.45m, depth=1.95 m).

CTFW N

2m

1.2m


Cryostat Service Structure


The Cryo-Cooler• The EGO-CTF cryo-cooling

system is initially based on pulse tube refrigerators (PTR).

• The PTR essentially achieves criogenic temperature by expanding high pressure He gas to low pressure ( 2Hz).

• Compression/expansion cycles are source of low frequency excess noise (INFN Roma1 measurements).

• the INFN Roma1 group on this item has already achieved experience on the PTR noise reduction (see task C1).

PT410W:

Power: 7.2kW @ 50Hz

Stage1: 40W @ 25K

stage2: 1W @ 4.2K

Threshold:0W @ 2.8K

Cooling: Liquid

Acoust.N: 70dB @1m

PT410W:

Power: 7.2kW @ 50Hz

Stage1: 40W @ 25K

stage2: 1W @ 4.2K

Threshold:0W @ 2.8K

Cooling: Liquid

Acoust.N: 70dB @1m


Jellyfish Prototype

• Working Principle:– Superattenuator filters

coupled with high compliance and thermal conductivity metal strips not degrading the isolation performance in all d.o.f.

Al / Cu

~1 m ~ 40 cm

1 cm

30 cm


Performed Test

1x1x70 cm Aluminum

l=60 cm

Set of stripes

•Negligible stiffness, negligible effects on Q (measured)•Enough thermal conductivity at 4 K (on paper)

Test ApparatusTest Apparatus

1) Parallel to Y KY = 2.4 N/m

2) Parallel to X KX = 11.4 N/m

3) Rotation around Z KΘZ = 3.5 N/m

4) Rotation around X KΘX = 3.0 N/m


Conclusions-A payload prototype has been designed and a preliminary thermo-mechanical FEA has been performed (C1 +C3 tasks) (Deliv. January 2005).

-The activity of the Pisa group at the EGO cryogenic facility will allow the build up of the necessary expertise to design a superattenuator cryogenic test facility.

-A small scale suspension prototype is going to be installed at INFN Pisa lab.

-The work done on the jellifish prototype has already produced some positive preliminary results .

-The experimental activity started at the INFN Pisa lab has had many points of interaction with the C1 task activity. It has been extablished the collaboration with the INFN Roma1and the Leiden Univ. groups. Strong support has been received from EGO.

STREGA WP2 - Task C3

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