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
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.)
ILIAS-GW General Meeting
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C3 Task - Main Activities
• 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)
ILIAS-GW General Meeting
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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:
•
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
-6
4x10
-6
3x10
-6
2x10
-6
1x10
-6
2000
0
1000
5000
-1
-1
4000
-1x10
3000
-6
0
20
40
60
0
80 100 120 140 160 180 200 220 240 260 280 300
Temperature [K]
ILIAS-GW General Meeting
Thermal Conductivity [W m K ]
•
6000
5x10
-1
– thermal expansion coefficient shows two zero
crossings at 123K and 17K.
Thermal expansion coefficient [K ]
•
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Payload Design and Mechanical FEA
210 Hz
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Payload Thermal FEA
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Two alternative solutions to mirror heat extraction problem
COLD FINGER
COLD FINGER
Cryostat
Very
Soft
Joints
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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
ILIAS-GW General Meeting
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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
ILIAS-GW General Meeting
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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
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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
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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.
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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.
ILIAS-GW General Meeting
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EGO Cryogenic Test Facility
W
CTF
N
2m
1.2m
• 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).
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Cryostat Service Structure
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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).
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PT410W:
Power: 7.2kW @ 50Hz
Stage1: 40W @ 25K
stage2: 1W @ 4.2K
Threshold:0W @ 2.8K
Cooling: Liquid
Acoust.N: 70dB @1m
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Jellyfish Prototype
Al / Cu
• Working Principle:
– Superattenuator filters
coupled with high
compliance and thermal
conductivity metal strips
not degrading the isolation
performance in all d.o.f.
~1 m
~ 40 cm
30 cm
1 cm
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Performed Test
Test Apparatus
l=60 cm
1x1x70 cm Aluminum
Set of stripes
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
•Negligible stiffness, negligible effects on Q (measured)
•Enough thermal conductivity at 4 K (on paper)
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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.
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