Cooling the ET payloads

Fulvio Ricci

Talk outline Assumptions for cooling the

LF Interferometer

HF Interferometer the thermal input evaluation and wires for the mirror suspension

Payload Material for the reaction mass

for the e.m. actuators

The thermal links : material

geometry

mechanical transfer function

thermal resistance

Cooling strategies LF : cryo-fluid vs. cryo-generator

Mechanical vs boiling noise

HF cooling or heating?

Assumptions Two independent interferometers

Main advantage: commissioning and data taking activity in parallel

Two kinds of attenuator chains Superattenuators with different performances

Cryogenic solution also for the HF interferometer for Thermal lensing compensation

Mirror and coating thermal noise

LF Int. and thermal noise

HF Int. and thermal noise

Payload mechanical Issues Large Masses:

reduces the recoils (good for suspension thermal noise )

increases the violin modes (good for control)

reduces the vertical modes (not good for control)

excess thermal load

Wires Length Increment

reduces the pendulum frequencies (good for suspension thermal noise )

reduces the violin modes (not good for control)

reduces the vertical modes (not good for control)

Wires Diameter Increment:

increment of the wire sections (good for cooling)

reduces the violin mode frequencies (not good for control)

reduces the dilution factor (not good for suspension thermal noise )

7

4

   . 0    /

       

     0. 0

10

3 3Ti6Al4V

Ti6Al4V

Ti6Al4V

Ti6Al4V

Mechanical @ 2 K

Density 44532 1 kg m

Young Modulus Y 127 Pa

Poisson Ratio 4 3

Loss Angle

Young Mo

G

4 3

/ / . 0 /

   0.0     / /

( ) 8.8 10 0

3Ti6Al4V Ti6Al4V Ti6Al4V

Ti6Al4V

dulus gradient:

1 Y dY dT 46 1 1 K

Thermal @ 2 K

Specific Heat C 7 J kg K

up to 3 K

Heat Conductivity

C T T

   0.14   / /

  .7 0   / /

Ti6Al4V

3Ti6Al4V

K W m K

Thermal Expansion 1 1 m m K

Ti6Al4V

   2.3315 0    /

  

189 

3 3si

si

Mechanical @ 10 K

Density 1 kg m

Young Modulus(100) Y 132 GPa (100)

GPa (111)

Poisson Ra

9

5

   0.22

10

/ / 7.7 0 /

   0.276    / /

si

si

si si si

si

tio

Loss Angle

Young Modulus gradient (100):

1 Y dY dT 1 1 K

Thermal @ 10 K

Specific Heat C J kg K

10

   2330   / /

4.85 0   / /

-6 -1

si

si

Thermo-Optic coef dn/ dT @ 30K: 5.8 10 K

Heat Conductivity K W m K

Thermal Expansion 1 m m K

Si

Material Properties

Measuring in Rome the thermal conductivity of the links and the suspension wires

Potenza immessa

Conducibilità termica

PT Cryomech multistage

sample CuBe3

Old Silicon sample prepared by micropulling

Payload for the LF case.PAYLOADMARIONETTE: (TI6AL4V WIRE)d = 3 mm, M1: 400 kg, L=2 m T=2 KMIRROR (SILICON WIRE) dimensions: diam 45cm, thickness 30cm (limit of present technology)d = 3 mm, M2: 110 kg, L=2 m T=10 K (only 18kW in cavity, 600 mm enough for heat extraction)RECOIL MASS (SILICON WIRE)d = 3 mm, M3: 110 kg L=2 m T=10 K Modes: pendulum 0.28 Hz, 0.36 Hz, 0.50Hz

vertical 0.4 Hz (blades), 20 Hz, 26 Hzviolins 33 Hz, 67 Hz, 100 Hz, 200 Hz, …

M1

M2

M3

COATING @ 10 K Ti:Ta2O5 SiO2

Losses @10K: 3.8 10-4 5 10-4

Standard Coating :

END Mirror: HL(19)HLL

INPUT Mirror: HL(8)HLL

PAYLOADMARIONETTE: (TI6AL4V WIRE)d = 3 mm, M1: 400 kg, L=2 m T=2 KMIRROR (SILICON WIRE) dimensions: diam 45cm, thickness 30cm (limit of present technology)d = 8 mm, M2: 110 kg, L=2 m T=10 KRECOIL MASS (SILICON WIRE)d = 5 mm, M3: 110 kg L=2 m T=10 K Modes: pendulum 0.28 Hz, 0.36 Hz, 0.50Hz

vertical 0.4 Hz (blades), 23 Hz, 62 Hzviolins 15.8 Hz, 31.6 Hz, 63.2 Hz, 126.4 Hz, …

M1

M2

M3

COATING @ 10 K Ti:Ta2O5 SiO2

Losses @10K: 3.8 10-4 5 10-4

Standard Coating :

END Mirror: HL(19)HLL

INPUT Mirror: HL(8)HLL

Payload for the HF case.

13

Design of a Full Scale Cryogenic Payload

•Marionetta Reaction Mass (MRM)•Ti alloy cable (low thermal conductivity) Ti-6Al-4V

•Marionetta

•Mirror silicon Wires•Reaction Mass high conductive wires

•Reaction Mass •(Dielectric material)

•Silicon mirror

Marionette

Epoglass G11 arms

•Body in amagnetic Steel (AISI316L)•Tungsten ( or CuW) insert• Epoglass arms G11 (suitable for cryo applications) •Copper plate to clamp the suspension wires and the thermal links

Tungsten

Mass for balancing the marionetteby an electric motor

Recoil Mass

To act as cryo trap (TRR < Tmirror)

To protect the mirror from shocks, from pollution and wire breaks ;

To support the coils for mirror actuation

• Center of mass coincident with the mirror one;• Suspension plane passing through the center of mass;• 4 back coils, 1 lateral coil;• Lateral (one side) holes for mirror position monitoring;• Materilas: SS + Dielectric material for the coils (epoglass);

Design main characteristics

Function

Material for the recoil mass: HF Int.

days days

Pressure [mbar]

The evolution of vacuum into the VIRGO tower for old (purple) and new (black) payloads

Old payload Al reaction mass

New payload TekaPeek, a high vacuum compatible plastic

Alternative suggestion: Vespel ® Polyimide, an ultra-high vacuum compatible, easily machined,and an excellent insulator from DuPont. Unfortunately Vespel outgassing ~5 times higher than that of peek

Approximate outgassing rates to use for choosing vacuum materials or calculating gas loads (All rates are for 1 hour of pumping)Vacuum MaterialStainless Steel Aluminum Mild Steel BrassHigh Density Ceramic Pyrex

Vacuum MaterialViton (Unbaked) Viton (Baked)Outgassing Rate(torr liter/sec/cm2)6x10-9 7x10-9 5x10-6 4x10-6 3x10-9 8x10-9Outgassing Rate(torr liter/sec/linear cm)8 x 10-7 4 x 10-8

18

Outside : Steel AISI316LInside: High density cermics tungsten carbide (WC) ceramics with a density of 15.5 g/cm3

Safety stops

The length of the RM can be changed according to mirror dimensions

Design for HF will integrate the TCS components

Recoil MassHigh-density ceramics and their manufactureYamase O.: Fuel and Energy, 38 (issue 4), July 1997 , pp. 257-257(1)

19

Same kind of Coil - Magnet System used in Virgo: Nb-Ti wires embedded in a copper matrix

Coil and Magnet Size can be changed according to constraints given by locking.

Electrostatic actuators easily adapted

Piero Rapagnani3/11/2008

Electromagnetic actuators

20

Virgoo F7 legs and coils: 84 kgo Marionette (AISI316L): 100

kg o Reaction Mass(Al6063): 60

kgo Mirror (Suprasil): 21 kg

o Overall payload weight: 181 kg

ETo Marionette

(AISI316L+Tungsten+epoglass): 400 kg

o Reaction Mass (AISI316L+Peek): 140 kg

o Mirror (Suprasil for HF, Silicon for LF ): 110 kg

o Overall payload weight: 650 kg

Comparing the Payloads

21

Design of the cooling system

Tanks to R. Passaquieti

3

•The upper part is thermally insulated by thermal screens

Cryo-Compatible Superattenuator design

Thermal Links I

Geometries

A corona of thin beamsLong Braids

Thermal Links II: mechanical transfer function measurements at low temperature

Evidence of a negligible influence of braids in the case of the torsion degrees of freedom

Pure Materials as aluminum and copper RRR = rroom temperature / ro where ro resid. resist. at T~0 K

Thermal Links III

Solution for the stationary state

Use of a high purity material

k~2000 W/m/K in the range 1-10 K

Thermal link length 20 m

Thermal difference at the link ends ~ 1K

HF Int. ~ 10 W: ~60 wires r~1 mm

LF Int. ~200 mW ~8 wires r~1 mm

Thermal Links IV

Epoglass

LVDT at low temp

Supercondcting wires

Solutions from the previous ILIAS experience

Elastic support

Piezo actuators

27

Reducing the vibration Cooling mirrors reduces all those noises temperature dependent.

Vibration noise of the refrigetation system (~0.01 - 0.03 mm/(Hz)1/2) kept under control.

Improved attenuation is possible by controlling other degrees of freedom and adding a Pt which operates@180o of phase

•The upper part is thermally insulated by thermal screens

Cryo-Compatible Mirror suspension design

Evaluation for the thermal inputs(Order of magnitude )

Payload chamber: φ ∼1.5 m h~3 m -4 K shield (25 layers s.u.) ~ 0.4 W - 77 K shield (75 layers s.u.)~35 W

Auxiliary tower: φ∼1 m h~2 m -4 K shield (25 layers s.u.) ~ 0.3 W -77 K shield(75 layers s.u.) ~ 27 W

Cryo trap: φ∼1.2 m L4K~ 100 m (L77K > L4K)- 4 K shield (25 layers s.u.) ~ 10 W-77 K shield (75 layers s.u.) ~ 1 kW ( relaxing the thermal input requirement from the hot hole we canassume L4K~ 50 m)

In the cryotrap case the cryofluid solution seems unavoidable

For each test mass we need 2 towers and 2 cryostats :

Assuming a mirror of t~300 mm f~ 450 mm ( 400 is available already but soon we can hope in silicon slabs of 450 mm in diameter ) m~ 110kg

The test mass is hosted in an inner cylindrical vacuum chamber f~ 1.5 m h ~ 4 m external cryostat f~ 2 m h ~ 4.5 m

Cold element tower which includes filters f~ 1.5 m h ~ 4.5 m

Cold

box

Vac.

Tube

Mirror

4 K cryo trap

~ 100m

~ 2 m

~ 1.5m

Cryotraps for the vacuum tubes and test mass cryostat

300 K

Cryofluid solution : the boiling problem( not present in the superfluid case)

Displacement amplitude and frequency spectrum shape depend on the tank material and geometry: typical pressure fluctuation 20 dBa 2 10-4 Pa. For example in the case of the GW resonant antenna Explorer xrms ~ 10-10 m @ 4K with an evaporation rate of a liquid Helium ~2 lt/h Example of the noise characteristics of a boiling

fluid in cylindrical container

Open points for the discussionDo we agree to assume still that HF is a cryo detector?-If yes, the operating temperature is defined mainly by the optimization of the heat extraction from the mirror ( max thermal conductivity)-If not, we have to review the thermal noise contribution on the ET-HF sensitivity curve

The cooling time - We need to reduce it ( up to 1 week per mirror )

- use of the He gas exchange, a complex solution in a real GW interferometer

- Use a telescopic system to transmit the refr. power via solid