STREGA & ET - 4th ILIAS-GW general meeting

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STREGA legacy for ET

Michele Punturo

INFN Perugia

STREGA & ET - 4th ILIAS-GW general meeting

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STREGA target• The STREGA mission is the development of

the technologies needed to reduce the thermal noise in the GW detectors by a factor 10 respect to the advanced detectors design– The target is the 3rd generation detectors

• STREGA is born as European (FP6) support and glue for the R&D activities already (and independently) started by the different GW research group in Europe

STREGA & ET - 4th ILIAS-GW general meeting

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ET

• Einstein GW Telescope– Design study submitted to the European Commission

under the 7th Framework Programme• Project in the negotiation phase

– Conceptual design of a 3rd generation GW interferometric detector

• Fully dedicated session tomorrow• Cryogenic suspension is one of the keywords of the possible

design of ET• No R&D activity expected inside the ET DS projects• Obviously the outcomes of STREGA are of fundamental

importance for the ET design phase

STREGA & ET - 4th ILIAS-GW general meeting

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Sensitivity evolution

1st generation2nd generation3rd generation ?

1 10 100 1000 1000010

-25

10-24

10-23

10-22

10-21

10-20

10-19

Thermal Noise

Seismic

Shot Noise

STREGA contribution

STREGA & ET - 4th ILIAS-GW general meeting

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Reduction of the thermal noise

• Reduction of the suspension and bulk thermal noise– New materials at cryogenic temperature

• Jena University research on CaF2 substrates– http://www.ego-gw.it/ILIAS-GW/documents/London_Talks/2nd_day/Jena-Nawrodt

.ppt

• Glasgow University research on Si substrates and blades

• INFN (Fi, Pg, Pi) measurements on Si fibres

STREGA & ET - 4th ILIAS-GW general meeting

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Advantages of the cryo-suspensions• Reduction of the Brownian thermal

noise– <X2>~T

• Reduction of the thermo-elastic noise– <X2>~T2

– Some “magic” behavior of special material

S.Reid et al.

M.Alshourbagy et al.

STREGA & ET - 4th ILIAS-GW general meeting

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Problems of a Cryo-Suspension• A GW detector has many noise constrain that make very

difficult the realization of a cryo-suspension• STREGA started the first studies of the compatibility of the

cryo-technologies with a GW detector suspension system– Low noise cryo-cooler (Roma 1)

STREGA & ET - 4th ILIAS-GW general meeting

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… problems of a cryo-suspension• Realization of a full Si Payload• Extraction of the large amount of heat deposited by the

high power laser light circulating in the FP cavities – EGO R&D activity with STREGA collaboration

• EGO, INFN Pi, et al.

• http://www.ligo.caltech.edu/docs/G/G050529-00/G050529-00.ppt

90 50 100 150 200 250 300

1.0x10-5

1.5x10-5

2.0x10-5

2.5x10-5

3.0x10-5

3.5x10-5 4th mode undoped Ta

2O

5

4th mode, TiO2 doped Ta

2O

5

Me

cha

nic

al l

oss

of c

oa

ted

sili

con

ca

ntil

eve

r

Temperature (K)

Coatings• Coating thermal noise will be dominant in the 2nd

generation GW detectors• Groups participating to STREGA are studying the possible

scenario in a 3rd generation detector

•Coating loss measured in a single layer doped tantala coating applied to Si cantilever substrate

0 50 100 150 200 250 300

1E-5

1E-4

1E-3

0.01

Temperature [k]

Uncoated slab Coated slab B Coating

Cobalt doped tantala (LMA production) on FS substrate(F. Travasso et al.)

STREGA & ET - 4th ILIAS-GW general meeting

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Escaping from the coating problem• Problems due to high power laser and transmittive

optics• Reduce the coating thickness

– High reflectivity grating waveguide coatings

• Use a different approach:– Full reflective optics and grating coatings

http://wwwcascina.virgo.infn.it/collmeetings/presentations/2006/2006-10/TNworkshop/burmeister_tnws_ego06.pdf

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Studies in Glasgow on silicate bonding of silica in relationto the Advanced generation and future GW detectors

Bond mechanical &thermal properties

Bond structuralproperties

Settling time

experiments

S. Reid et al.,PLA 363 341-345 (2006)

Activation energy:Ea = 0.545 eV permolecule of OH−

Above plot showing settling time as a function of

temperature for silica-silica bonds

Above plot showing two bonded silica cylinders, studied before and after

silicate bonding.

Experiments suggest that the level of loss associated with

silicate bonding may lie:bond ~ (0.3→1.2)×10-1

SEM SEM

TEM

TEM

AFM

(81±4) nm

7.9 GPa

measurements Firenze/Glasgow

STREGA & ET - 4th ILIAS-GW general meeting

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Direct thermal noise measurement• An interferometer devoted to direct measurement of

thermal noise in fused silica suspensions and composite structures built using hydroxy-catalysis (silicate) bonding has been realized in Glasgow– Mike Plissi e al.

• Excess noise from the reference cavity is currently limiting the thermal noise measurement• Work in progress

STREGA & ET - 4th ILIAS-GW general meeting

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STREGA legacy for ET

• The WITCH is not dead, hence it is too early to talk about legacy– ET is a conceptual design study

• Any R&D budget is included in ET design study, but in the proposal it is stated that ET will benefit of the R&D activities already active in Europe

– STREGA must act as the solutions supplier for ET

– STREGA people must enter in the ET Science Team

• Discussion after this session