Transcript kokeyama-100723-Birmingham

Large-scale Cryogenic Gravitationalwave Telescope, LCGT
Keiko Kokeyama
University of Birmingham
23rd July 2010
Friday Science
Contents
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
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”
Keiko Kokeyama 23 July 2010 @ Friday Science
0/28
Gravitational Waves
Ripples of spacetime propagating at the speed of light.
Changing the distances between free particles.
Coalescences of
neutron star binaries,
Supernova, BH
coalescences, etc.
y
x
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.
Significances of the direct detection
Experimental verification of the general relativity
The GW astronomy
Keiko Kokeyama 23 July 2010 @ Friday Science
1/28
Gravitational Wave Detectors
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
Mirror
Mirror
Beamsplitter
Bright
Laser
Dark
Photo detector
Super accurate measurement to detect 10-20m change per 1 m
Keiko Kokeyama 23 July 2010 @ Friday Science
2/28
Large Scale ground-based GW detectors
The 1st Generation Detectors
GEO600
VIRGO
LIGO
TAMA300
Upgrading to the 2nd Generation Detectors
Advanced LIGO, Advanced VIRGO, GEO HF, LCGT
Keiko Kokeyama 23 July 2010 @ Friday Science
3/28
LCGT project
On 22nd June, the Japanese Next Generation Detector,
LCGT was funded
 9.8 billion yen (£75M) for three years including 2010.
 selected one of the projects for the forefrontresearch-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.
Keiko Kokeyama 23 July 2010 @ Friday Science
4/28
Scientific Goals
Establish the GW astronomy
Main goal:
to detect gravitational waves from
neutron star binaries (1.4 solar mass)
at about 200 Mpc with > S/N 8
Expecting a few events
in a year from:
Coalescences of neutron star
binaries
Goal sensitivity:
h=3 ×10-24 [m/rtHz] at 100Hz
Keiko Kokeyama 23 July 2010 @ Friday Science
5/28
GW detector network
 LCGT plays a role of Asia-Oceania center among other detectors
Best sensitivity direction for
LCGT
LIGO Hanford
LIGO Livingston
VIRGO
The good-sensitivity directions
are complementary for other detectors
Keiko Kokeyama 23 July 2010 @ Friday Science
6/28
Technical Features of LCGT
(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
Keiko Kokeyama 23 July 2010 @ Friday Science
7/28
(1) Underground Site
Keiko Kokeyama 23 July 2010 @ Friday Science
8/28
(1) Underground Site
Keiko Kokeyama 23 July 2010 @ Friday Science
9/28
(1) Underground Site
Keiko Kokeyama 23 July 2010 @ Friday Science
10/28
(1) Underground Site
More than 2 orders of
magnitude better than
TAMA site
The variance of 46 hours is about 0.1~0.2 degrees
without temperature-controlling
Keiko Kokeyama 23 July 2010 @ Friday Science
11/28
(2) Seismic isolation system
 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.
Keiko Kokeyama 23 July 2010 @ Friday Science
12/28
(2) Seismic isolation system
 Inverted pendulum
 Three GAS (Geometric antispring) 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
↓
2-stage suspension (Low temperature)
Keiko Kokeyama 23 July 2010 @ Friday Science
13/28
(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 f 250 ×150mm, 30kg
Keiko Kokeyama 23 July 2010 @ Friday Science
14/28
(3) Cryogenic
 Heat links are used to release the heat occurred by the
laser beam on the test-masses
SAS, 300 K
Heat link 1W,
7 × f1mm, Al
Heat link 1W,
5 × f3mm Al
Recoil Masses
will be suspended by
Sapphire or Al wires
Bolfur wire
40cm, f1.8mm
10K
Sapphire wire, 860 mW
40cm, f1.8mm
20K
8K,
100K
 Similar type to CLIO refrigerator (Sumitomo Heavy
Industries Ltd, Pulse-tube refrigerator)
Keiko Kokeyama 23 July 2010 @ Friday Science
15/28
(4) Optical configuration
Main IFO
Keiko Kokeyama 23 July 2010 @ Friday Science
16/28
(4) Optical configuration
Main IFO
Resonant-Sideband-Extraction (RSE)
FP cavity
In addition to the Fabry-Perot (FP) arm
cavities, Power recycling and signal
extraction cavities (PRC and SEC,
respectively) are added to the interferometer
FP cavity
Advantages in capability of high laser
power in arm cavities and flexibility in
observation band
Keiko Kokeyama 23 July 2010 @ Friday Science
PRC
SEC
17/28
(4) Optical configuration
Operation modes
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
FP
PRC
FP
SEC
Keiko Kokeyama 23 July 2010 @ Friday Science
18/28
(4) Optical configuration
Operation modes
DRSE configuration has the best floor-level sensitivity at
BRSE configuration has wider band. It
around 100 Hz, and the good observable distance for neutronstar inspiral events. Therefore the detuned configurations have
advantages in the first detection and expected number of
events.
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.
Keiko Kokeyama 23 July 2010 @ Friday Science
19/28
(4) Optical configuration
Operation Strategy
Operate in the V-DRSE mode first for earlier detection of
gravitational-wave signals
After the first few detections, they will switch to the VBRSE mode.
Keiko Kokeyama 23 July 2010 @ Friday Science
20/28
Technical Background
Suspended 4m RSE
Keiko Kokeyama 23 July 2010 @ Friday Science
21/28
CLIO
 In Kamioka mine
 Prototype ifo for LCGT
 To demonstrate the thermal noise reduction using cryogenic technique
100m base-line unrecombined Fabry-Perot Michelson interferometer
Beam-splitter
Fabry-Perot
cavity
Fabry-Perot
cavity
Keiko Kokeyama 23 July 2010 @ Friday Science
22/28
Design sensitivity of CLIO
Keiko Kokeyama 23 July 2010 @ Friday Science
23/28
Cryogenic in CLIO

2008: 300K design sensitivity
achieved.

300K mirror thermal noise
dominates the sensitivity around
150Hz.

2009: Both near mirrors were
cooled at about 20K.


The suspended
sapphire mirror
(f100×60, 2kg)
2010: Sensitivity around 150Hz
were improved.
6-stage vibration isolation
(3 stages in 300K,
3 stages in cryogenic)
Total mirror thermal noise were
reduced.
Low vibration refrigerator
Keiko Kokeyama 23 July 2010 @ Friday Science
24/28
Displacement in November 2008
 Almost the thermal
noise limited at 300K
(4/2008 to 12/2008)
 Clio displacement
touched the predicted
thermal noise level
Sapphire mirror themal noise
Suspension
thermal noise
(20-80 Hz)
Keiko Kokeyama 23 July 2010 @ Friday Science
25/28
Reduction of Mirror Thermo-Elastic Noise
Two near mirrors are cooled down to 20 K
 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.
Keiko Kokeyama 23 July 2010 @ Friday Science
26/28
Reduction of Mirror Thermo-Elastic Noise
CLIO has finally demonstrated the reduction of the
thermal noise on sapphire mirrors around 200 Hz
Keiko Kokeyama 23 July 2010 @ Friday Science
27/28
Summary
LCGT
Just funded! The overview of LCGT project such as underground site,
Seismic isolation system, cryogenic, optical configuration were
reviewed.
CLIO
As 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
Keiko Kokeyama 23 July 2010 @ Friday Science
28/28
End
Supplement slide (1)
Wave length
1064
1546
Initial Laser
Power
Arm cavity
Finesse
150
Arm power
gain
9984 = 960 x
10.4
Arm power
(single arm)2
420.5 =\=
374.4 = 75
*9984 /2 kW
Injecting Laser 78.48 (in
Power into
total), 75
IFO
(carrier)
Modulation
depth
0.3 for both
Arm cavity
cut-off
frequency
PR gain
10.4
PRC power on
BS
780 = 75 *
10.4 W
RF freq 1
11.25M (PM)
RF freq 2
45.00M (AM)
MC1 length
10.0
PR cavity cutoff frequency
MC2 length
13.324109
MC1 Finesse
TBD
PR-Arm cutoff frequency
MC2 Finesse
TBD
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 ???
Supplement slide (2)
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
Reflectivity
FM
Reflectivity
FM
radius/thickn
ess
PRM
radius/thickn
ess
SRM
radius/thickn
ess
BS
radius/thickn
ess
0.996
PRM
Reflectivity
0.9
SRM
Reflectivity
0.8464 =
0.922
BS
Reflectivity
0.5
HR Coating
Loss of EM,
45e-6
FM, PRM and
SRM
BS Loss
EM
radius/thickn
ess
0.999945
100e-6
25 / 15 cm
Transmissivit
y
0.999
25 / 15 cm
AR
Transmissivit
y
AR Coating
Loss
1000e-6
1 - R - Loss
TBD
TBD
TBD
Bulk loss
(absorption)
(large
optics ??? for
Sapphire: ???
FM, EM)
Bulk loss
(absorption)
(small
optics ??? for
Fused
Silica: ???)
20 ppm
2.5
OMC length
1.5 m
Beam radius
3 cm
Young's modulus
of Sapphire
4e11
Pa
OMC Finesse
2000
Suspension length
40 cm
Density of
Sapphire
4e3
kg/m^3
Diameter of
suspension fiber
1.8 mm
Poisson ratio of
Sapphire
0.29
Number of
suspension fiber
5.6e-9
1/K
4
Thermal
expansion of
Sapphire (20K)
Specific heat of
Sapphire (20K)
0.69
J/K/kg
Thermal
conductivity of
Sapphire (20K)
1.57e4
W/m/K
OMC
input/output
mirror
reflectivity
OMC end
mirror
reflectivity
TBD
TBD
Temperature of
suspension
16 K
OMC MC FSR
???
Mechanical loss of
fiber
2e-7
Thermal
expansion of
Sapphire (300K)
5.0e-6
1/K
DC readout
phase
134.7 deg
Mirror radius
12.5 cm
Specific heat of
Sapphire (300K)
790
J/K/kg
Mirror thickness
15 cm
40
W/m/K
Bulk absorption
20 ppm/cm
Thermal
conductivity of
Sapphire (300K)
Young's modulus
of Silica
7.2e10
Pa
Poisson ratio of
Silica
0.17
Refraction index
of Silica
1.45
1e-8
Thermal
expansion of
Silica (300K)
5.1e-7
1/K
9
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
121.8d eg
Control Bandwidth
Quantum
efficiency
CARM
control band
width
DARM
control band
width
0.9
30k Hz
200 Hz
Coating absorption 0.1 ppm
Temperature of
mirrors
Mechanical loss of
a mirror
Number of coating
layers (ITM)
20 K
Number of coating
layers (ETM)
18
50 Hz
Mechanical loss of
Silica coatings
1e-4
SRC control
band width
50 Hz
Mechanical loss of
Tantala coatings
4e-4
Optical loss of
each arm
70 ppm/roundtrip
FeedForward gain
-0.97
(openloop),
1/(1-0.97) =
30 (closed
loop)
PRC control
band width
50 Hz
MICH control
band width
Optical loss in the
SRC
Optical loss at the
PD
1/K
2%
Specific heat per
volume of Tantala 2.1e6
(300K)
J/K/m^3
10%
Thermal
conductivity of
Tantala (300K)
33
W/m/K
dn/dT of Tantala
(300K)
14e-6
1/K
Suppliment slide (3)
Suppliment slide (3)
Reduction of Suspension Thermal Noise
Vacuum tanks
Vacuum level

2 x 10-7 Pa
Vacuum duct

3km length
 1m diameter
 steinless steel