Suspension Thermal NoiseGiles Hammond (University of Glasgow)

on behalf of the Strawman Red Team

GWADW 2012, 18th May 2012LIGO-G1200579

2

Suspension Design

• Let suppose that we subtract Newtonian noise. What is the lower limit in frequency for thermal noise?

• (1) aLIGO reference

• (2) Warm upgrades

• (3) Cold upgrades

3

aLIGO Monolithic Stage

Steel wires

Penultimate mass

Ear

Steel wire break-off prism

Silica fibres

End/input test mass

Ear

4

Finite Element Analysis• Use FEA to predict energy stored in the suspension elements and the dilution

A.V. Cumming et al., Class. Quant. Grav., 215012, 2009A.V. Cumming et al., Class. Quantum Grav. 035003, 2012

• Model:

– bulk loss– surface loss– thermoelastic loss – weld loss– Bond loss

• Energy storage in fibre essential to model thermal noise performance

22224

22 4

ototalo

totaloB

mTkx

5

aLIGO Thermal Noise (Single Test Mass)

10-19m/Hz @ 10Hz

6

Warm Upgrade• Reduce the loss in suspension elements (surface loss and weld loss are roughly

equal contributions to aLIGO thermal noise)

• Improve dissipation dilution by increasing suspension length or thickening fibre ends to enhance energy distribution (e.g. 5mm stock rather than 3mm stock)

• LASTI violin modes: FEA and measurements agree 15%

7

Warm Upgrade

• Factor of 3 improvement in thermal noise and seismic noise from longer suspension and improved fibre geometry

• Noise is soon limited by vertical cantilever springs

8

Cold Upgrade

Silicon TPen

Silicon TMirror

• Cryogenic options utilise Silicon as a suspension material

• Fibres used to extract heat. Depending on temperature the geometry can be limited by strength (126-200 MPa) or heat extraction

• In Strawman Red we have been developing code to optimise the different noise sources with temperature dependent parameters

• At T<40K surface loss dominated

• Bounce mode frequencies are higher than aLIGO

• Violin mode frequencies are lower than aLIGO

9

Cold Upgrade

• Significant improvement in thermal noise performance (>10 over aLIGO at 10Hz)•“Warmer” version is limited by Silicon strength, “Colder” version limited by heat extraction