Current status of Japanese gravitational wave detectors
Koji Arai (National Astronomical Observatory of Japan)
for LCGT project (including TAMA collaboration / CLIO collaboration)

LCGT Projectm Large Cryogenic Gravitational wave Telescope
Key features of LCGT- Cryogenic mirrors (T~20K)=> suppression of thermal noises- Underground site at Kamioka=> quiet seismic activity- km-class baseline=> 3km arm lengthm LCGT suspension- Sapphire cryogenic mirrors=> m~30kg, heat transfer
by sapphire monolithic suspension- Suspension Point Interferometer=> isolation from heat link vibration- Seismic Attenuation Systemfor the room temp vibration isolation

SAS: 3 stage antivibration system withinverted pendulum

Vacuum is commonRadiation outer shield
SPI auxiliary mirror
Heat links start from thisstage to inner radiation shield

Sapphire fibersuspension

Main mirror

Conceptual design of LCGT suspension

m LCGT development
Task sharing by two prototype interferometers
TAMA300: Interferometer technologies, Sensitivity at kHz-band
SAS development, Digital control system

m LCGT interferometer- 150W laser source- Optical configuration:Resonant Sideband Extraction

CLIO:- Expected binary range
185Mpc for NS-NS binary inspiral(SNR10, from optimum direction)

Displacement sensitivity, Thermal noise reduction
Cryogenic technologies

Estimation of fundamental noises for LCGTTAMA Interferometer

CLIO Interferometerm TAMA interferometer- Located at Mitaka near Tokyo- 300m arm length- Fabry-Perot Michelsonwith power recyclingm CLIO interferometer- Located at Kamioka mine
- 100m arm length- two orthogonal Fabry-Perot arms
- Sapphire mirror cooled at 20K

300mm TAMA target- Development of TAMA-SAS=> International collaboration
with LIGO / Univ of Pisa
- Establishment of interferometer technologies=> Interferometer sensing and control
m TAMA-SAS- Low freq vibration isolation
Inverted pendulum
Vertical filters (MGAS)
Double pendulum suspension- Passive isolation + active damping

m CLIO target- Demonstration of mirror cooling=> heat link design / suspension design- Demonstration of thermal noise reduction by mirror cooling=> pursue of displacement sensitivity- Experience of underground site operation=> infrastructures / working time limitation / safety

300m

IP topinvertedpendulum(IP)m Mirror cooling- Heat link to an upper suspension stage => 5N Al wire heat contact- Al fiber suspension (0.5mm in dia.)- Low vibration PT refrigerators- Mirror successfully cooled up to 12-14K

MGAS filter(Monolithic
Geometric Anti-Spring)

platform

double pendulumwith recoil mass

Structure of TAMA-SAS

Installation of TAMA-SAS

3

Per arm end mirror
Start: 2007/04/27, 1 :05

2

2008/10/10 Current best

-16

10Sapphire
test mass

54
3

2-18

10-19102103

Frequency [Hz] 10-1310dL- sensitivity
Intensity noise
Alignment noisedl- feedback noisedl+ feedback noise
Shot noise
Detector noise
Det+ShotFrequency noise (err)
Upconversion noise-1410-15

10-16

10-1710-18

10Mirror Temp

Inner top
Outer top
Cryo-cooler 2nd head
5m duct mid
Cryo-baseUpper mirror
Mirror612.9K
8.82K

540m CLIO sensitivity- Sensitivity at 300K=> 2.5x10-19m/rtHz @250Hz- 300K goal achieved:
close to the sensitivity limit- mirror thermal noise=> thermoelastic damping isdominant at 300K

50100150 164
Time [hour]

200

250

300

Cooling profile of the cryogenic components.
The test mass temperature reached 13K after 164h of cooling.

heat removal from the test mass
via aluminum wires

-1710

1/2

upper mass

10-15

10

Displacement noise [m/Hz ]heat linkwire

Temperature [K]

1/2

2003/11/04 Previous best

Sensitivity improvement of TAMA with TAMA-SAS- Noise contribution estimated=> low freq. excitation
experiment revealed
upconversion noise is limiting
the sensitivity at 100~500Hz

62.9K

6-1410

CLIO sensitivity at 300K-1210

2008/11/05 CLIO sensitivity-1310

Seismic noise estimation
51/2=> owing to reduced angularmotion of the test massin the 1Hz-10Hz band10(2008/10/10)

100Displacement noise [m/Hz ]- Achieved reduction of alignment
control noise with TAMA-SAS-13

Displacement noise [m/Hz ]m TAMA sensitivity- Sensitivity improvement=> 4x10-19m/rtHz @1kHz

TAMA300 Displacement Sensitivity

Suspension thermal noise (Q~10 )

-14

10

Mirror thermal noise
Shot noise

-15

10-16

10-17

10-18

10-19101102310

10Frequency [Hz]Current best displacement sensitivity of CLIO interferometer-1910-20m Future plan toward LCGT
- Implement of Resonant Sideband Extraction=> Establishment of length/alignment control scheme
1023Frequency [Hz]1010
Estimation of the noise contribution for TAMA300

m Future plan toward LCGT- Realize noise reduction by cooling of the mirror=> Now being carrying out:
Refinement of the cryogenic suspension
and the interferometer system

410