Large-scale Cryogenic Gravitational-wave Telescope, LCGT

Large-scale Cryogenic Gravitational-wave Telescope, LCGT

Keiko KokeyamaUniversity of Birmingham

23rd July 2010Friday Science

General introduction of LCGT project

Introduction of gravitational waves (GWs)

Introduction of LCGT

Science goal and impact

Technical features Underground, Seismic isolation system, Cryogenic, Optical configuration,

Operation modes

Technical background CLIO project as a LCGT prototype

0/28Keiko Kokeyama 23 July 2010 @ Friday Science

Contents

Photos and plots are from “LCGT design document, “ CLIO/LCGT talks by Miyoki-san and Yamamoto-san, and “Study report on LCGT interferometer observation band”

Gravitational Waves

y

x

Significances of the direct detection

Coalescences of neutron star binaries, Supernova, BH coalescences, etc.

Einstein predicted its existence as a consequence of the general relativity in 1916.

Its existence is verified indirectly by the binary-neutron star observation, however, the direct detection has not been successful yet.

Ripples of spacetime propagating at the speed of light. Changing the distances between free particles.

Experimental verification of the general relativityThe GW astronomy

Experimental verification of the general relativityThe GW astronomy


Gravitational Wave Detectors

Super accurate measurement to detect 10-20m change per 1 m

Bright

DarkPhoto detector

Beam-splitter

Laser

Mirror

Mirror

Laser interferometer (ifo) type GW changes the mirror positions The path length difference is detected as the

phase difference between the two paths GW has a very weak interaction to matters - very

small path length change


GEO600

VIRGO TAMA300

LIGO

Upgrading to the 2nd Generation Detectors

Advanced LIGO, Advanced VIRGO, GEO HF, LCGT

The 1st Generation Detectors

Large Scale ground-based GW detectors


On 22nd June, the Japanese Next Generation Detector, LCGT was funded

LCGT project

9.8 billion yen (£75M) for three years including 2010.

selected one of the projects for the forefront-research-development-strategic subsidy (40 billion yen in total) of Ministry of education, culture, sports, science and technology, Japan

The purpose of this subsidy is to develop the environment for the young or female scientists, and internationally high level researches

Further budget is being requested to run the project after the 3rd year. The result will be appear in August.


Scientific Goals

Establish the GW astronomyMain goal:to detect gravitational waves from neutron star binaries (1.4 solar mass) at about 200 Mpc with > S/N 8

Expecting a few eventsin a year from:Coalescences of neutron star binaries

Goal sensitivity:h=3 ×10-24 [m/rtHz] at 100Hz


GW detector network

LCGT plays a role of Asia-Oceania center among other detectors

Best sensitivity direction forLCGT

LIGO HanfordLIGO Livingston

VIRGO


The good-sensitivity directionsare complementary for other detectors

(1) Underground Site

(2) Seismic isolation system

(3) Cryogenic Technique Thermal noise design, Substrate of test mass

(4) Optical configuration Four configurations and the observation plan

Technical Features of LCGT








The variance of 46 hours is about 0.1~0.2 degrees without temperature-controlling

More than 2 orders of magnitude better than TAMA site




Requirement: -190 dB at 3 Hz including the suspension part (*) and seismic isolation system

Seismic level in Kamioka is 10-9 m/rtHz at 3Hz Sensitivity requirement is 3x10-18 m/rtHz at 3 Hz

The seismic isolation system (room temperature) is required -130 dB isolation


(*) Test masses are suspended so that they act as free masses. Suspensions play a role of isolating the seismic motion, too.

↓2-stage suspension (Low temperature)



Inverted pendulum Three GAS (Geometric anti-spring) filters

This system achieves isolation ratios of:-160dB for horizontal (w/ 4 stages) at 3 Hz-140 dB for vertical (w/ 3 stages) at 3 Hz

These satisfy the requirement

(3) Cryogenic

We want to reduce the thermal noise Thermal noise is…

To reduce the thermal noise, the main mirrors and suspension are cooled down to 20 K by refrigerators

sapphire 250 ×150mm, 30kg


8K,100K

Heat link 1W, 5 × 3mm Al

Heat link 1W, 7 × 1mm, Al

SAS, 300 K

20K

10K

Sapphire wire, 860 mW40cm, 1.8mm

Bolfur wire40cm, 1.8mm

Recoil Masseswill be suspended bySapphire or Al wires

Heat links are used to release the heat occurred by the laser beam on the test-masses

(3) Cryogenic

Similar type to CLIO refrigerator (Sumitomo Heavy Industries Ltd, Pulse-tube refrigerator)


(4) Optical configuration

Main IFO


Main IFOResonant-Sideband-Extraction (RSE)

In addition to the Fabry-Perot (FP) arm cavities, Power recycling and signal extraction cavities (PRC and SEC, respectively) are added to the interferometer

Advantages in capability of high laser power in arm cavities and flexibility in observation band

FP cavity

FP cavity

SECPRC



BRSE: Broad band operation The carrier laser light is anti-resonant in SEC. Detector observation band is tuned to have a maximum sensitivity for neutron-star inspiral events.

DRSE: Detuned RSE. Detuning is a technique to increase detector sensitivity only in a slightly narrow frequency band. It is realized by controlling the SEC length between resonance and anti-resonance condition for the carrier laser beam.

V-BRSE: Broad band operation + slightly off resonance in the arm cavity

V-DRSE: Detuned operation+ slightly off resonance in the arm cavity

Operation modes



PRC

SEC

FP

FP

BRSE configuration has wider band. It can provides longer observation duration for an inspiral event. It is good for extracting information from observed waveforms, in accuracy of estimated binary parameters, the arrival time, and so on.

V-BRSE and V-DRSE have both advantages.

DRSE configuration has the best floor-level sensitivity at around 100 Hz, and the good observable distance for neutron-star inspiral events. Therefore the detuned configurations have advantages in the first detection and expected number of events.

Operation modes



Operate in the V-DRSE mode first for earlier detection of gravitational-wave signals

After the first few detections, they will switch to the V-BRSE mode.

Operation Strategy



Technical Background

Suspended 4m RSE


CLIO

In Kamioka mine Prototype ifo for LCGT To demonstrate the thermal noise reduction using cryogenic technique100m base-line unrecombined Fabry-Perot Michelson interferometer

Fabry-Perotcavity

Beam-splitterFabry-Perotcavity


Design sensitivity of CLIO


2008: 300K design sensitivity achieved.

300K mirror thermal noise dominates the sensitivity around 150Hz.

2009: Both near mirrors were cooled at about 20K.

2010: Sensitivity around 150Hz were improved.

Total mirror thermal noise were reduced.

2008: 300K design sensitivity achieved.

300K mirror thermal noise dominates the sensitivity around 150Hz.

2009: Both near mirrors were cooled at about 20K.

2010: Sensitivity around 150Hz were improved.

Total mirror thermal noise were reduced.

Low vibration refrigerator

The suspendedsapphire mirror (100×60, 2kg)

6-stage vibration isolation (3 stages in 300K, 3 stages in cryogenic)

Cryogenic in CLIO


Displacement in November 2008

Almost the thermal noise limited at 300K (4/2008 to 12/2008)

Clio displacement touched the predicted thermal noise level

Suspension thermal noise(20-80 Hz)

Sapphire mirror themal noise


Two near mirrors are cooled down to 20 K

Reduction of Mirror Thermo-Elastic Noise

It took 250 hours for cooling the mirror. The near mirrors were cooled at 16.4k and inner shield was cooled at 11.5k. The outer shield of the mirror tank and center of the cryogenic vacuum pipe were cooled at 69k and 49k, respectively.


Reduction of Mirror Thermo-Elastic Noise

CLIO has finally demonstrated the reduction of the thermal noise on sapphire mirrors around 200 Hz


Summary

LCGTJust funded! The overview of LCGT project such as underground site, Seismic isolation system, cryogenic, optical configuration were reviewed.

CLIOAs the prototype for LCGT, CLIO successfully demonstrated the thermal noise reduction. Cryogenic, underground techniques are established for LCGT

Note:Some parameters and materials are still under discussion toward the final design


End

Supplement slide (1)

Wave length 1064

Initial Laser Power 150

Injecting Laser Power into IFO

78.48 (in total), 75 (carrier)

Modulation depth 0.3 for both

RF freq 1 11.25M (PM)

RF freq 2 45.00M (AM)

MC1 length 10.0

MC2 length 13.324109

MC1 Finesse TBD

MC2 Finesse TBD

Arm cavity Finesse 1546

Arm power gain

9984 = 960 x 10.4

Arm power (single arm)2

420.5 =\= 374.4 = 75 *9984 /2 kW

Arm cavity cut-off frequency

PR gain 10.4

PRC power on BS

780 = 75 * 10.4 W

PR cavity cut-off frequency

PR-Arm cut-off frequency

SR gain 11 (not checked yet)

Arm cavity length 3006.69 m

PR cavity length 73.2826 m

Asymmetry length 3.33103 m

BS-FM length 25 m

SR cavity length 73.2826 m

SRC detuning phase 86.5 3.4 ???

EM mass 30

FM mass 30

PRM mass TBD

SRM mass TBD

BS mass TBD

EM ROC 7113.900 m

FM ROC 7113.900 m

FM AR ROC TBD

PRM ROC TBD

SRM ROC TBD

BS ROC Infinity

EM radius/thickness

25 / 15 cm

FM radius/thickness

25 / 15 cm

PRM radius/thickness

TBD

SRM radius/thickness

TBD

BS radius/thickness

TBD

EM Reflectivity 0.999945

FM Reflectivity 0.996

PRM Reflectivity 0.9

SRM Reflectivity

0.8464 = 0.922

BS Reflectivity 0.5

HR Coating Loss of EM, FM, PRM and SRM

45e-6

BS Loss 100e-6

Transmissivity 1 - R - Loss

AR Transmissivity

0.999

AR Coating Loss 1000e-6

Bulk loss (absorption) (large optics ??? for Sapphire: ???FM, EM)

20 ppm

Bulk loss (absorption) (small optics ??? for Fused Silica: ???)

2.5

OMC length 1.5 m

OMC Finesse 2000

OMC input/output mirror reflectivity

TBD

OMC end mirror reflectivity

TBD

OMC MC FSR ???

DC readout phase 134.7 deg 121.8d eg

Control Bandwidth

Quantum efficiency 0.9

CARM control band width

30k Hz

DARM control band width

200 Hz

PRC control band width 50 Hz

MICH control band width 50 Hz

SRC control band width 50 Hz

Feed-Forward gain

-0.97 (openloop), 1/(1-0.97) = 30 (closed loop)

Supplement slide (2)

Beam radius 3 cm

Suspension length 40 cm

Diameter of suspension fiber 1.8 mm

Number of suspension fiber 4

Temperature of suspension 16 K

Mechanical loss of fiber 2e-7

Mirror radius 12.5 cm

Mirror thickness 15 cm

Bulk absorption 20 ppm/cm

Coating absorption 0.1 ppm

Temperature of mirrors 20 K

Mechanical loss of a mirror 1e-8

Number of coating layers (ITM) 9

Number of coating layers (ETM) 18

Mechanical loss of Silica coatings 1e-4

Mechanical loss of Tantala coatings 4e-4

Optical loss of each arm 70 ppm/roundtrip

Optical loss in the SRC 2%

Optical loss at the PD 10%

Young's modulus of Sapphire 4e11 Pa

Density of Sapphire 4e3 kg/m^3

Poisson ratio of Sapphire 0.29

Thermal expansion of Sapphire (20K)

5.6e-9 1/K

Specific heat of Sapphire (20K) 0.69 J/K/kg

Thermal conductivity of Sapphire (20K)

1.57e4 W/m/K

Thermal expansion of Sapphire (300K)

5.0e-6 1/K

Specific heat of Sapphire (300K) 790 J/K/kg

Thermal conductivity of Sapphire (300K)

40 W/m/K

Young's modulus of Silica 7.2e10 Pa

Poisson ratio of Silica 0.17

Refraction index of Silica 1.45

Thermal expansion of Silica (300K)

5.1e-7 1/K

Specific heat per volume of Silica (300K)

1.64e6 J/K/m^3

Thermal conductivity of Silica (300K)

1.38 W/m/K

dn/dT of Silica (300K) 8e-6 1/K

Young's modulus of Tantala 1.4e11 Pa

Poisson ratio of Tantala 0.23

Refraction index of Tantala 2.06

Thermal expansion of Tantala (300K)

3.6e-7 1/K

Specific heat per volume of Tantala (300K)

2.1e6 J/K/m^3

Thermal conductivity of Tantala (300K)

33 W/m/K

dn/dT of Tantala (300K) 14e-6 1/K

Suppliment slide (3)

Reduction of Suspension Thermal Noise

Suppliment slide (3)

Vacuum tanks

Vacuum level 2 x 10-7 Pa

Vacuum duct 3km length 1m diameter steinless steel

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Large-scale Cryogenic Gravitational-wave Telescope, LCGT

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