Suspension Upgrades for Enhanced Interferometers Giles Hammond Institute

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Suspension Upgrades for Enhanced Interferometers Giles Hammond (Institute for Gravitational Research, SUPA University of

Suspension Upgrades for Enhanced Interferometers Giles Hammond (Institute for Gravitational Research, SUPA University of Glasgow) 18 th - 22 nd May 2015 LIGO-G 1500598 GWADW Alaska 1

Overview • Motivation for warm and cold suspensions • Noise terms • Some possible

Overview • Motivation for warm and cold suspensions • Noise terms • Some possible topologies – Higher stress a. LIGO suspensions – Longer warm suspensions (40 kg -80 kg) – Cold upgrade scenarios – Hybrid suspensions • Summary 2

Motivation for Suspension Upgrades Warm upgrades (e. g. A+, ET-HF, Cosmic Explorer) • Fused

Motivation for Suspension Upgrades Warm upgrades (e. g. A+, ET-HF, Cosmic Explorer) • Fused silica • 80 kg - 160 kg test masses • 60 cm - 120 cm suspension lengths • 800 MPa – 1. 5 GPa stress in fibres Cold upgrades (e. g. LIGO Voyager, ET-LF) • Silicon at 20 K - 120 K • 143 kg/200 kg test masses • 60 cm/100 cm suspension lengths • Warm upgrades with fused silica offer a well developed technology and improvements in strain sensitivity at low frequency of up to 3. • Cryogenic upgrades for LIGO Voyager offer potential improvements in strain sensitivity of 8. A V Cumming et al 2014 Class. Quantum Grav. 31 025017 G D Hammond et al 2012 Class. Quantum Grav. 29 124009 3

Noise Terms • Suspension thermal noise – uses a combination of analytical and FEA

Noise Terms • Suspension thermal noise – uses a combination of analytical and FEA dilution – horizontal, vertical and violin thermal noise • Coating thermal noise – uses finite test mass correction (Somiya and Yamamoto, Phys. Rev. D 79, 102004, 2009 – optimised a. LIGO coatings (16 131 nm Ta 2 O 5 and 17 182 nm Si. O 2) • Seismic Noise – uses DCC note by Shapiro et al. (T 1300786) to estimate transmissibility (longitudinal and vertical) – uses BSC requirements for ISI seismic noise (actually slightly better at 10 Hz) 4

1. Higher Stress (>O 1/A+) • LLO alog: posted 18: 59, Wednesday 29 April

1. Higher Stress (>O 1/A+) • LLO alog: posted 18: 59, Wednesday 29 April 2015 - last comment - 07: 14, Thursday 30 April 2015 (17946) • Keeping current a. LIGO test suspension geometry, and operating at 1. 5 GPa would push bounce/roll to 6 Hz/9 Hz, and violin modes to 680 Hz A Heptonstall et al 2014 Class. Quantum Grav. 31 105006 5

1. Higher Stress (>O 1/A+) • Keep end section at 800 m, but thin

1. Higher Stress (>O 1/A+) • Keep end section at 800 m, but thin middle section to 300 m (1. 5 GPa). Use 5 mm stock to improve dilution. • 1. 5 GPA is 3 safety factor • 350 m suspension (1. 1 GPa) demonstrated at LHO during a. LIGO SUS weld training (April 2015) A Cumming et al 2009 Class. Quantum Grav. 26 215012 6

1. Higher Stress (>O 1/A+) a. LIGO suspension=5 10 -23/ Hz @10 Hz •

1. Higher Stress (>O 1/A+) a. LIGO suspension=5 10 -23/ Hz @10 Hz • Minimal upgrade, only change final stage fibre geometry • Ready by early 2016 with robustness testing (e. g. O 1 upgrade or A+) 7

2. Longer Suspensions (A+, Explorer) a. LIGO suspension=5 10 -23/ Hz @10 Hz •

2. Longer Suspensions (A+, Explorer) a. LIGO suspension=5 10 -23/ Hz @10 Hz • Longer suspensions (final stage 1. 1 m) and higher stress offer further improvements for both 40 kg and 80 kg 8

3. Cold Suspensions (ET-LF/Voyager) LIGO Voyager assumes radiative cooling ET-LF assumes conduction cooling ET-LF

3. Cold Suspensions (ET-LF/Voyager) LIGO Voyager assumes radiative cooling ET-LF assumes conduction cooling ET-LF fibre: 1. 75 mm Voyager ribbon: 2. 5 mm 0. 5 mm Parameter Voyager ET-LF Geometry Ribbon Fibre Power (MW) 3 0. 018 L (m) 0. 6 1 Mass (kg) 143 200 Test Mass (K) 124 20 Pen. Mass (K) 77 4 thermal (mm) - 1 strength (mm) 2. 5 0. 5 1. 5 Stress (Gpa) 0. 3 9

3. Cold Suspensions (ET-LF/Voyager) • Just showing suspension thermal noise for LIGO Voyager and

3. Cold Suspensions (ET-LF/Voyager) • Just showing suspension thermal noise for LIGO Voyager and ET-LF • This is a best case as: – dilution will be lower for real ribbons/fibres ( 2 -3 when necks are included) – bond attachments and associated noise need to be included => community needs to work on robust modelling (more discussion in breakout session)

4. Hybrid Suspensions • Hybrid suspensions are those which utilise silica fibres but with

4. Hybrid Suspensions • Hybrid suspensions are those which utilise silica fibres but with a silicon test mass (e. g. G 1500312 -v 1) • Silica has broad dissipation peak at low temperature. But can you still benefit from lower temperature operation Smith et al. , G 1500312 • Travaso et al. , Materials Science and Engineering A 521– 522 (2009) 268– 271 11

4. Hybrid Suspensions • Similar to a. LIGO performance until 240 K, but then

4. Hybrid Suspensions • Similar to a. LIGO performance until 240 K, but then worse performance than a. LIGO f=10 Hz Hybrid a. LIGO • a. LIGO uses thermoelastic cancellation to meet 10 Hz requirement • For cold silica, need to increase fibre diameter to maintain cancellation=> dilution gets worse • T<240 K, thermoelastic dominates until much lower temperature=> this pushes up thermal noise • see talk by Marielle van Veggel (breakout session) • Challenges also with jointing materials with different CTE=>induced stress 12

Summary • There a variety of suspension topologies which improve thermal noise performance Parameter

Summary • There a variety of suspension topologies which improve thermal noise performance Parameter High stress (e. g. A+) Longer suspension (e. g. A+, Explorer) Cold suspension (e. g. Voyager) Hybrid suspension 10 Hz improv. 1. 25 2 -3 8 (Voyager), 60 (ET-LF) Not better than 1. 04 Hardware changes None modest-significant Bounce mode 6 Hz 5 Hz 21 Hz 6 Hz Violin mode 680 Hz 370 Hz 300 Hz 680 Hz Stress 1. 5 GPa 350 MPa(1) 1. 5 GPa Readiness <1 year 2 -3 year 3 -5 years • • (1): grown fibre tensile stresses will likely be higher To understand full benefit need to include quantum noise and Newtonian noise 13