Thermal Noise performance of advanced gravitational wave detector

suspensions

Alan Cumming, on behalf of the University of Glasgow Suspension Team

5th April 2011

2

Overview

• Silica suspension design for aLIGO

• Prototype aLIGO suspension

• Thermal noise performance and loss modelling

• Current status

• Future work

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aLIGO Monolithic Silica Stage

Steel wires

Penultimate mass

‘Ear’

Silica fibres

End/input test mass

‘Ear’

Requirement: 10-19m/Hz @ 10Hz

Upper metal masses (22kg

masses)

Blade springs

Lower Monolithic silica stage

(40kg masses)

Prototype Suspension, MIT

• Laser pulled silica fibres

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A. Heptonstall et al., Rev. Sci. Inst. 82, 011301 (2011) Fibres laser welded to ears

Complete suspension

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Ear

FibreNeck

Stock Weld

Finite Element Analysis

• Use FEA to predict energy stored in the suspension elements and the dissipation dilution, D

elastic

total

E

ED

A. Cumming et al., Class. Quant. Grav., 215012, 2009,A. Cumming et al., Class. Quant. Grav., in preparation,

2011.

Ear Horn

Modelling the suspension loss

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• Internal friction described by the mechanical loss of the system • For a suspension this originates from various different mechanisms in the fibre ends:

• Modelling with FEA gives

Surface loss, surf

Bulk loss, bulk

Weld loss, weld

Thermoelastic loss, th

weldbulksurfthtotal

1 D

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Modelling comparison with measured

A. Cumming et al., Class. Quant. Grav., in preparation, 2011

• Measurement of horizontal noise difficult

• Modelling compared by predicting loss of violin modes

of suspension fibres

• Measured on MIT prototype suspension

• Gives good confidence in modelling technique

Violin mode FEA Frequency (Hz)

Measured

Frequency (Hz)

Projected loss from

FEA model Measured loss

Fundamental 511 511,520 1.50 x 10-9 1.61 x 10-9

1st harmonic 1017 1020 1.75 x 10-9 2.16 x 10-9

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aLIGO Final Stage Noise (Single Test Mass)

10-19m/Hz @ 10Hz

A. Cumming et al., Class. Quant. Grav., in preparation, 2011

99

Current status and future work

• Suspension design for aLIGO now finalised

• Preparation for the start of manufacture of production suspensions for first installations into the LIGO instruments is currently ongoing

• First installations timetabled for summer 2011

• Studies already ongoing on methods to further increase sensitivity for enhancements to aLIGO using the FEA modelling techniques

• Application of modelling to future third generation detectors using different materials and possibly cooled to cryogenic temperatures

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Thermal Noise Model

22224

22 4

ototalo

totaloB

m

Tkx

hornweldfibretotal

1

D

• Use the following loss terms to model the welds, ear horns and fibres

n totalelastic

n2

totalelastic

21

totalelastic

1

E

E

E

E

E

E

2

2

ticthermoelas1

YC

YTo

d

h s 8surface

77.011bulk 102.1 f

7weld 108.5

A.M. Gretarsson et al., Phys. Rev. A, 2000 G. Cagnoli and P.A. Willems, Phys. Rev. B, 2002P.A. Willems, T020003-00M.Barton et al., T080091-00-KA. Heptonstall et al., Phys. Lett. A, 354, 2006A. Heptonstall et al., Class. Quant. Grav, 035013, 2010