Design study for 3rd generation interferometers Work Package 1 Site Identification

Jo van den Brand

e-mail: jo@nikhef.nl

LISA

Third generation detector

Rüdiger, ‘85

Two order of magnitude compared to initial Virgo

Underground site

Multiple interferometers:

– 3 Interferometers; triangular configuration?

– 10 km long

– 2 polarization + redundancy

Design study part of ILIAS & FP7

Construction: 2010-16 ?

LISA

Scientific justification for 3rd generation ITF

Primordial gravitational waves

Production: fundamental physics in the early universe- Inflation, phase transitions, topological defects- String-inspired cosmology, brane-world scenarios

Spectrum slope, peaks give masses of key particles & energies of transitions

A TeV phase transition would have left radiation in 3G band

LISA

Introduction

Features of 3rd generation ITF

• Sensitivity below 10-24 m/sqrt(Hz)

• Ultra-low frequency cut-off

• Vibration isolation

• Sensitive in range 0.1 – 10 Hz

• Multiple sites for signal correlation

• Advanced optical schemes (squeezed light)

• Cryogenic optics

• Underground sites

• 10 kilometer arms

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Ultra Low Frequency: 1Hz

3rd generation1 Hz cutoff

1st - 2nd generation 10 Hz cutoff

One more decade

at low frequency

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Isolation requirements

Required isolation @1 Hz: at least 1010 with ground noise.

Ultra soft vibration isolation

– Long pendulums (50, 100 m)

– Very good thermal stabilization

Active platforms

– Very low noise sensors

– Very good thermal stabilization

– Very low tilt noise

Very quiet site

LISA

Site identification process

Even pressure fluctuations due to weather are a relevant source of gravity gradient noise [11].

V. N. Rudenko, A. V. Serdobolski, K. Tsubono, “Atmospheric gravity perturbations measured by a ground-based interferometer with suspended mirrors”, Class. And Quant. Grav., vol. 20, pp. 317-329.

10-5

10-4

10-3

10-2

10-9

10-8

10-7

10-6

10-5

10-4

frequency ( Hz )

ac

ce

lera

tio

n (

g /

sq

rt (

Hz

) )

component 2component 1

Seismic measurements at LNGS

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LIGO Site selection criteria

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LIGO Site evaluation criteria

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LIGO Site evaluation criteria

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Seismic noise attenuation

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Not only seismic noise…

Direct action of wind on buildings

Strong correlation between mirror motion and wind speed at f < 0.1 Hz

Detector operation more difficult in

windy days, duty cycle affected

Even more difficult in the future, with

high finesse cavities

LISA

Underground interferometers

LISM: 20 m Fabry-Perot interferometer, R&D for LCGT, moved from Mitaka (ground based) to Kamioka (underground)

Seismic noise much lower:102 overall gain103 at 4 Hz

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LISM at MitakaLISM at Kamioka limit by isolation system

Interferometer operation becomes much easier underground.Noise reduced by orders of magnitude

S.Kawamura, ‘02

Hz

Dis

plac

emen

t sp

ectr

um m

/RH

z

LISA

Large-scale Cryogenic Gravitational-wave Telescope: LCGT

LISA

CLIO – Prototype for LCGT

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LISM in Kamioka

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ILC, NLC, Tesla, VLHC, Muon Source – Site requirements

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ILC, NLC, Tesla, VLHC, Muon Source – Site requirements

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Isolation shortcircuit

Newtonian noise

00( ) . ( )

( )

Gh f const x f

H f

Figure: M.Lorenzini

SEISMIC NOISE

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Seismically generated Newtonian noise

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Newtonian noise estimate

Cella-Cuoco, 98

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NN reduction

Surface waves give the main contribution to newtonian noise

Surface movement dominates the bulk compression effect

Surface waves

Compression waves

Courtesy: G.Cella

Surface waves dieexponentially with

depth:

GO UNDERGROUND!

LISA

NN reduction in caves

Reductionfactor

Cave radius [m]

Spherical CaveG.Cella

5 Hz10 Hz20 Hz40 Hz

NN reduction of 104 @5 Hzwith a 20 m radius cave

106 overall reduction (far from surface)

(Compression waves not included)

102 less seismic noise x 104 geometrical reduction

LISA

1 10 100 1000 1000010-25

10-24

10-23

10-22

10-21

10-20

10-19

h(f) [1

/sqrt(H

z)]

Frequency [Hz]

(a) 3rd Generation (b) LCGT (c) advanced LIGO (d) advanced Virgo (e) LIGO (f) Virgo (g) GEO600

(a)

(b) (c)

(d)

(e)

(f)(g)

1st generation2nd generation3rd generation

New

tonian

noise

Ground surface

Underground

LISA

NN from compression waves

In a spherical cave NN is reduced as 1/R3

Beam direction is more important.

Credit: R. De Salvo

ELLIPSOIDAL?

MAKE LARGE CAVERN

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A possible design

Upper experimental hall

Credit: R.De Salvo

50-100 m well to accomodatelong suspension for low frequency goal

Ellipsoidal/spherical cave fornewtonian noise reduction

10 km tunnel

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Site identification process

Gran Sasso

Salt mines

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Complementarity with LIGO, VIRGO and LISA

RotatingNeutron Stars

Vast range in wavelength(8 orders of magnitude)

LIGO/VIRGOLISA

Frequency [Hz]

3rd ITF

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Summary

Expected features of 3rd generation ITF

– Triangular configuration

– Advanced optical schemes

– Low-frequency isolation and suspension

– Cryogenic optics

– Multiple underground sites

Design study

– Develop preliminary ideas

– Define site identification process