Compact Advanced Passive Isolation Stages · Compact Advanced Passive Isolation Stages for Third...

MG13 Stockholm June 2012

Compact Advanced Passive Isolation Stages for Third Generation Gravitational Wave Detectors

Li Ju, Jean-Charles Dumas, Siddartha S Verma, Chunnong Zhao, David Blair


Outline •  Requirements for 3rd generation detectors •  Review of available technologies •  Comparison of isolation techniques •  New Approaches

– Euler LaCoste vertical stage – Roberts linkage horizontal stage with internal

actuation


Motivation

S. Hild et al, Class. Quantum Gravi. 27 (2010) 015003

•  3rd generation detectors aiming to achieve GW detection sensitivity ~1Hz

•  ET vibration isolation concept proposed 17m - 50m super attenuator type chains

Can ET isolation performance be obtained in a compact design?


Different Ultralow Frequency Stages •  Vertical

–  Geometric Anti-Spring (GAS) –  LaCosta Stage

•  Horizontal –  Invert Pendulum –  Roberts Linkage

•  Blade springs, Euler springs

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Comparison of Different Techniques

Invert Pendulum Roberts Linkage

Technique Compressive flexure Tensile wire Stress High compressive stress Pure tension Internal modes

Long rods Tensile wire violin


Synthetic Pendulums (horizontal)

m m

Comparison of Different Techniques

GAS LaCoste (with coil springs)

Stress High stressed negative springs (load orthogonal to stress)

Pre-stressed zero length springs

Internal modes

Blade spring modes Coil spring normal modes

Stability Dislocation flows * Creep


Synthetic Vertical Stages

*R. DeSalvo, A. DiCintio and M. Lundin, Eru. Phys. J. Plus, 126:75 (2011)

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Zero length spring

Concept of Zero Length Spring


negative length

spring

Force

Displacement

!l =L (zero length spring,

effective initial length l0=0) !l=L+l (negative length spring,

effective initial length l0=-l)

zero length spring positive length spring

!l =L-L0 (positive length spring,

initial length l0=L0)

0 L0 -l L

Euler springs


l l

P

Comparison of blade springs & Euler Springs


Blade Springs Euler Springs Stored energy mgΔl small, mgΔl1~10-2mgΔl ✓ Spring mass ~kg ~grams ✓ Stress High Low Compressive stress

Low High

Frequency with load

Fixed by deflection Tunable (f~l length pendulum)

Internal f of spring element

Low High ✓

Can we combine benefits of Euler spring with low frequency performance of a LaCoste stage?



Euler Spring Module for Use in LaCoste Stage

•  High tensile strength Maraging steel •  Stable Tensional Euler module

Under tension Stable tensional Euler Module


Euler spring module performance (ring)

y = 1105.4x - 75.812

0

50

100

150

200

250

0.25 0.255 0.26 0.265 0.27 0.275 0.28

Displacement (m)

Forc

e (N

)


Euler-LaCoste Prototype

Parameters: Spring blades: length: 260mm

width: 20mm thickness: 0.5mm

Load: ~20kg

Extended wires+ negative length Euler spring to realize zero length spring


00.10.20.30.40.50.60.7

0 20 40 60 80Δx (mm)

Fre

quen

cy (

Hz) 300mm

290mm280mm270mm260mm

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15 20 25Dh (mm)

f (H

z)

L=432mmL=410mmL=395mmL=385mm

Frequency tuning with x-offset

Frequency tuning with h-offset

•  f~0.15Hz so far •  Expect improvement with better

engineered structure •  Expect lower frequency with large

scaled structure

Euler-LaCoste Prototype Frequency Tuning


Large Scale Euler-LaCoste

Design concept •  4 Euler modules replacing the coil

springs •  Height: 1m •  Maraging steel blades : 350mm x 20mm

x 1.5mm thick •  Max stress: 30% of yield (no observable

creep*) •  Load: 800kg •  Expected frequency: 50mHz

*Virdone, J. Agresti, et.al., Nucl. Instr. and Meth. A, 593, 597-607 (2008)


Roberts Linkage Horizontal Stage

f~50mHz

P moving in a shallow potential path


Improve the low frequency performance through thermal actuation

Electrical current through the suspension wire

•  DC to compensate slow drift* •  AC (low frequency) signal from

the bottom of the chain feedback to Roberts Linkage to suppress low frequency vibration

*J.C. Dumas et al. Rev. Sci. Instrum. 80, 114502 (2009)

Transfer function at low frequency



Conclusions

•  Euler springs allow tunable vertical suspension frequencies 0.3-1Hz

•  Euler-LaCoste allows 50mHz main suspension •  Robets allows 20mHz horizontal suspension •  low frequency (~50mHz) pre-isolation stages •  Elegant actuation system through resistive

heating of suspension wires •  These stages could allow improved

performance and more compact design for 3rd generation detectors

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