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Overview of Advanced LIGODavid Shoemaker

PAC meeting, NSF Review 5 June 2003, 11 June 2003

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Advanced LIGO

LIGO mission: detect gravitational waves and

initiate GW astronomyNext detector» Must be of significance for

astrophysics» Should be at the limits of

reasonable extrapolations of detector physics and technologies

» Should lead to a realizable, practical, reliable instrument

» Should come into existence neither too early nor too late

Advanced LIGO

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Initial and Advanced LIGO

Factor 10 higher amplitude sensitivity» (Reach)3 = rate

Factor 4 lower frequency bound» Binary inspirals» Stochastic

backgroundTunable response» Periodic sources» Broad-band bursts

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Design features

200 W LASER,MODULATION SYSTEM

40 KG SAPPHIRETEST MASSES

ACTIVE ISOLATION

QUAD SILICASUSPENSION

PRM Power Recycling MirrorBS Beam SplitterITM Input Test MassETM End Test MassSRM Signal Recycling MirrorPD Photodiode

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Comparison of key parameters

≥10-9 (100 Hz)≥10-12 (10 Hz)Seismic/Suspension System Horizontal Attenuation

Passive, 5 stage3 stage active, 4 stage passive

Seismic/Suspension Isolation System

25 cm32 cmMirror Diameter

Fused Silica, 11 kgSapphire, 40 kgTest Masses

0.84 ms5.0 msLight Storage Time in Arms

4 cm6 cmArm Cavity Power Beam size

30 kW800 kWOptical power on Test Masses

10 W180 WOptical Power at Laser Output

1064 nm1064 nmLaser Wavelength

<10-7 torr<10-7 torrVacuum Level in Beam Tube, Vacuum Chambers

4000 m4000 mFabry-Perot Arm Length

1×10-19 m/Hz-1/28×10-21 m/Hz-1/2Displacement Sensitivity (~200 Hz)

10-218×10-23Strain Sensitivity [rms, 100 Hz band]

LHO: 4km, 2km;LLO; 4km

LHO: 4km, 4km; LLO: 4km

Observatory instrument lengths;LHO = Hanford, LLO = Livingston

Initial LIGO Advanced LIGOSubsystem and Parameters

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Design ‘signature’

Low-frequency ‘brick wall’ from Newtownian background» Time-varying distribution of mass near test masses» Limit for ground-based interferometers» Isolation system renders seismic noise negligible at all frequencies

Thermal noise» Low-mechanical loss materials and assembly techniques» Monolithic fused-silica suspensions» Sapphire (baseline) test masses

Quantum noise» Greatest laser powers allowed by present materials; best use of that light» Fabry-Perot arm, signal-recycled Michelson» Allows optimization for astrophysics and instrumental limitations

Advanced LIGO's Fabry-Perot Michelson IFO is a platform for all currently envisaged enhancements to this detector architecture

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100 101 102 10310-25

10-24

10-23

10-22

f / Hz

h(f)

/ Hz1/

2

Optical noiseInt. thermalSusp. thermalTotal noise

Anatomy of the projected Adv LIGO detector performance

10-24

10-25

Newtonian background,estimate for LIGO sites

Seismic ‘cutoff’ at 10 Hz

Suspension thermal noise

Test mass thermal noise

Unified quantum noise dominates at most frequencies for fullpower, broadband tuning

10 Hz 100 Hz 1 kHz

10-22

10-23

Initial LIGO

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Scope of proposal

Upgrade of the detector» All interferometer subsystems» Data acquisition and control infrastructure

Upgrade of the laboratory data analysis system» Observatory on-line analysis» Caltech and MIT campus off-line analysis and archive

Virtually no changes in the infrastructure» Buildings, foundations, services, 4km arms unchanged» Move 2km test mass chambers to 4km point at Hanford» Replacement of ~15m long spool piece in vacuum equipment» Present vacuum quality suffices for Advanced LIGO

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Baseline plan

Initial LIGO Observation 2002 – 2006» 1+ year observation within LIGO Observatory» Significant networked observation with GEO, VIRGO, TAMA

Structured R&D program to develop technologies» Conceptual design developed by LSC in 1998» Cooperative Agreement carries R&D to Final Design, 2005

Proposal early 2003 for fabrication, installationLong-lead purchases planned for 2004, real start 2005» Sapphire Test Mass material, seismic isolation fabrication» Prepare a ‘stock’ of equipment for minimum downtime, rapid installation

Start installation in 2007» Baseline is a staggered installation, Livingston and then Hanford

Coincident observations by 2010

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Reference design options

Baseline is upgrade of 3 interferometers» in discovery phase, 3rd IFO serves to improve statistics (nongaussian noise), » improvement of sensitivity (roughly double event rate for 3 instead of 2 identical

interferometers), » quiet commissioning on second LHO IFO while observing with the LHO-LLO pair» allow better stochastic upper limits (co-located instruments)» potentially increase uptime in early phases of commissioning/observation

In observation phase, the same IFO configuration can be tuned to increase low or high frequency sensitivity

» sub-micron shift in the operating point of one mirror suffices» an optimization would require a change in signal recycling mirror transmission» could decide before commissioning, or after a period of observation» third IFO could e.g.,

– observe with a narrow-band VIRGO– focus alone on a known-frequency periodic source– focus on a coalescence or BH-ringing frequency of an inspiral detected by other two IFOs

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Reference design options

Baseline is to upgrade the 3rd interferometer from 2km to 4km» Could leave at 2km» Cost is modest and sensitivity gain supports discovery» Will certainly want maximum sensitivity later

Baseline is effectively a simultaneous upgrade of both sites» Could stagger quite significantly to maintain the network –

with an equally significant delay in completion and coincidence observations by the two LIGO sites

Baseline is to employ Sapphire as the test mass material» Fused silica an interesting fallback – more later

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Potential later incremental upgrades

Available as options in the future to fully exploit the Advanced LIGO platformTo address…» Low-frequency ‘brick wall’ from Newtownian background

– Regression techniques based on a seismometer grid may allow ~factor 10 reduction (shift down ~0.75 in frequency of ‘brick wall’)

» Thermal noise– Non-Gaussian ‘Top Hat’ beams in arms may lead to a significant reduction in

thermoelastic noise contribution» Interferometer topology

– Injecting ‘squeezed vacuum’ may allow broader sensitive region– Variable transmission signal recycling mirror could allow optimization of Q

and frequency of narrow-band mode

Reference Design is well defined, does not include the above

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Timing of Advanced LIGO

Observation of gravitational waves is a compelling scientific goal, and Advanced LIGO will be a crucial element» to detection if none made with initial LIGO» to capitalizing on the science if a detection is made with initial LIGO

Delaying Advanced LIGO likely to create a significant gap in the field – at least in the US» Encouragement from both instrument and astrophysics communities

Our LSC-wide R&D program is in concerted motion» Appears possible to meet program goals

We are reasonably well prepared» Reference design well established, largely confirmed through R&D

Timely for International partners that we move forward now

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Advanced LIGO

An exciting and significant step forward from first generation» instruments» potential for astrophysics

No fundamental surprises as we move forward; concept and realization remain intact with adiabatic changesA great deal of momentum and real progress in every subsystem

» Thorne: Astrophysics with Advanced LIGO» Fritschel: Systems, sensing, optics subsystems» Coyne: Mechanical subsystems, electronics, installation» Sanders: Cost and Schedule overview