lisbon, 8 january 20081 research and development for gravitational wave detectors raffaele flaminio...

Lisbon, 8 January 2008 1

Research and Developmentfor Gravitational Wave Detectors

Raffaele Flaminio

CNRS/LMA Lyon


Ground-based GW detectors

Focus on ground based laser interferometers Most sensitive detectors in operation LIGO, Virgo, GEO, TAMA, Some of the following applies to other kind of detectors (e.g. resonant detectors)


Present reach

Gravitational collapses in the galaxy (or nearby ones) Test upper limits of known galactic pulsars (and look for unknown ones) Search for coalescing neutron stars up to a max distance of ~ 30 Mpc Search for merger of binary black holes to a max distance of ~150 Mpc


Toward GW astronomy

Present detectors will test upper limits

Even in the optimistic case rate too low to start GW astronomy

Need to improve thesensitivity

Increase the sensitivity by 10 increase the probed volume by 1000

Plans to improve thepresent detectors


GW roadmap: time scale

E.T.

LISA

LIGO

GEO

Virgo

´22´21´20´19´18´17´16´15´14´13´12´11´10´09´08´07´06

E.T.

LISA

LIGO

GEO

Virgo

´22´21´20´19´18´17´16´15´14´13´12´11´10´09´08´07´06

Virgo+

LIGO+

Advanced Virgo

GEO HF

Advanced LIGO

DS PCP Construction Commissioning

HanfordHanford

LivingstonLivingston

Launch Transfer data

data

ET: Einstein Telescope Design study selected by the EU within FP7


GW roadmap: sensitivity scale

Ad LIGO/Virgo NB

1 10 100 1000 1000010-25

10-24

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h(f) [1

/sqrt(H

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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)

Credit: M.Punturo

LIGO 2005 AURIGA 2005

Advanced LIGO/Virgo (2014)

Virgo Design

GEO-HF2009

Virgo+ 2009

Einstein GW Telescope

DUAL Mo(Quantum Limit)


1 10 100 1000 1000010-23

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(a) Virgo Nominal sensitivity (b) Seismic noise (c) Pendulum thermal noise (d) Mirror thermal noise (e) Shot Noise

h(f) [1/

sqrt(H

z)]

Frequency [Hz]

(a)

(b)

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Present limitations ….

• Shot noise- Depends on quantum nature of light- Decreases when more photons are used- Depends on the optical configuration adopted


…. and possible improvements

• Increase power stored in the interferometer- increase laser power- decrease optical losses

• But pay attention to:

1) Mirrors heating and thermal lensing- better thermal compensation- decrease light absorption

2) Radiation pressure noise - increase mirror mass- optimize optical configuration

signal recycling- use non classical light

light squeezing/quantum optics

3) Non-linear coupling between the light fields and the mirror suspensions

1 10 100 1000 1000010-23

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h(f) [1/

sqrt(H

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Frequency [Hz]

(a)

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Present limitations …

1 10 100 1000 1000010-23

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sqrt(H

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Frequency [Hz]

(a)

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• Mirror thermal noise- brownian motion- due to temperature ….- …plus any source of friction in the mirror


… and possible improvements

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• Reduce friction in the mirrors

• Friction in the coating- Main source of friction today- Multi-layers SiO2/Ta2O5 used today- Ta2O5 is the lossy material

look for new materialsmaterials science

- SiO2 layer lossier than raw materialimprove deposition process

• Friction in the substrate- Best material so far: silica- Avoid attaching anything to preserve mechanical quality- Move to electrostatic actuators avoiding magnets attached to the mirror


Present limitations …

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h(f) [1/

sqrt(H

z)]

Frequency [Hz]

(a)

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• Pendulum thermal noise- same kind of brownian motion- due to temperature …- … plus friction in the suspension wires- or friction between the wires and the mirror


… and possible improvements

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sqrt(H

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Frequency [Hz]

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• Decrease pendulum friction- better suspensions wires (new materials)- better wire clamping- monolithic suspensions- fused silica fibers- silicate bonding


Further reduction of thermal noise

• Thermal noise decrease as √T- go to low temperatures- friction vs temperature?- depends on materials (materials science)- look for optical materials with good mechanical properties at low temperature (silica not a good choice)

• Thermal lensing- due to laser power deposited in the mirror- higher mirror thermal conductivity

lower thermal lensing- higher wires thermal conductivity

heat extraction more efficient

• Silicon- silicon a good candidate- silicate bonding behavior at low T?- thermal conductivity across bonding?- on-going R&D

Si


Cryogenics for GW detectors

• Need to cool large masses• Vibration free cryogenics• Soft thermal links• Points of contact with underground detectors for rare events search

COLD FINGER


ILIAS: the STREGA joint research activity

Strong component within the ILIAS project Goal: thermal noise reduction for GW detectors

All the european groups working in thermal noise reduction involved

INFN (Ge, Fi, Fr, Le, Pd, Pi, Pg, Rm1, Rm2), CNRS (LKB, ESPCI,LMA), Univ Glasgow, CNR (Trento), Leiden, Jena, …

All collaborations: Virgo, GEO, ROG, Auriga, MiniGRAIL Ingredients:

Cryogenics suspensions Cryogenics mirrors Materials Thermo-elastic studies

A key role for starting the ET design study A lot more to do But ILIAS ends in 2009 and support available

within ILIAS-NEXT very much reduced


Present limitations: seismic noise

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sqrt(H

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Frequency [Hz]

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• Seismic noise– residual transmission of seismic motion through the suspensions system– 'relatively large' motion at very low frequency

→ need for a control system→ control system noise

- sensitivity to weather conditions


Seismic noise: possible improvements

Better active isolation More sensitive accelerometers Very low-frequency tilt-meters Gryo-lasers

Softer springs ?

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Forthcoming limitations

Gravity gradient noise Limitation to existing infrastructure Will limit advanced detectors

Figure: M.Lorenzini

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Improvement: go underground !

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

102 overall gain103 at 4 Hz


Further improvements: spherical cavern

Reductionfactor

Spherical CavernG.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


Combination of improvements

Upper experimental hall

Credit: R.De Salvo

50-100 m tower to accommodatelong suspension for low frequency goal

Ellipsoidal/spherical cave fornewtonian noise reduction

10 km tunnel


The ET concept Need to improve sensitivity at low frequencies

More physics is there Present facilities limited by environmental disturbances

Seismic noise Gravity gradients

ET Einstein Telescope Concepts

Underground» Less seismic noise» No wind» Temperature stability

Cryogenic 30 km beam tube 100 m suspensions Different geometry

» Triangle?

Rüdiger, ‘85


Conclusion

Present detectors are testing upper limits of GW predictions A few upgrades ready to be implemented (Virgo+, Enhanced LIGO)

Advanced detectors should see several events/month Sensitivity will profit from on-going R&D (e.g. coating thermal noise) Engineering needed (e.g. monolithic suspensions)

ET Einstein Telescope Design study should start soon R&D activity started within FP6 (STREGA) Should continue within FP7 More investment needed Points of contact with other fields of astroparticle physics

» Cryogenics» Vibration isolation» Underground operation

GW will participate to ILIAS-NEXT GW networking Networking with underground labs A few small R&D activities But more investment will be needed

lisbon, 8 january 20081 research and development for gravitational wave detectors raffaele flaminio...

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