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
MG13 Stockholm June 2012
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
MG13 Stockholm June 2012
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?
MG13 Stockholm June 2012
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
MG13 Stockholm June 2012
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
MG13 Stockholm June 2012
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
MG13 Stockholm June 2012
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
MG13 Stockholm June 2012
l l
P
Comparison of blade springs & Euler Springs
MG13 Stockholm June 2012
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?
MG13 Stockholm June 2012
MG13 Stockholm June 2012
Euler Spring Module for Use in LaCoste Stage
• High tensile strength Maraging steel • Stable Tensional Euler module
Under tension Stable tensional Euler Module
MG13 Stockholm June 2012
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
)
MG13 Stockholm June 2012
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
MG13 Stockholm June 2012
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
MG13 Stockholm June 2012
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)
MG13 Stockholm June 2012
Roberts Linkage Horizontal Stage
f~50mHz
P moving in a shallow potential path
MG13 Stockholm June 2012
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
MG13 Stockholm June 2012
MG13 Stockholm June 2012
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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