Suspension Thermal Noise Giles Hammond (University of Glasgow) on behalf of the Strawman Red Team GWADW 2012, 18 th May 2012 LIGO-G1200579
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