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Transcript of Large-scale Cryogenic Gravitational- wave Telescope, LCGT Keiko Kokeyama University of Birmingham 23...
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
1/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
2/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
3/28Keiko Kokeyama 23 July 2010 @ Friday Science
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.
4/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
5/28Keiko Kokeyama 23 July 2010 @ Friday Science
GW detector network
LCGT plays a role of Asia-Oceania center among other detectors
Best sensitivity direction forLCGT
LIGO HanfordLIGO Livingston
VIRGO
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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
7/28Keiko Kokeyama 23 July 2010 @ Friday Science
(1) Underground Site
8/28Keiko Kokeyama 23 July 2010 @ Friday Science
(1) Underground Site
9/28Keiko Kokeyama 23 July 2010 @ Friday Science
(1) Underground Site
10/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
(1) Underground Site
11/28Keiko Kokeyama 23 July 2010 @ Friday Science
(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
12/28Keiko Kokeyama 23 July 2010 @ Friday Science
(*) 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)
(2) Seismic isolation system
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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
14/28Keiko Kokeyama 23 July 2010 @ Friday Science
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)
15/28Keiko Kokeyama 23 July 2010 @ Friday Science
(4) Optical configuration
Main IFO
16/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
(4) Optical configuration
17/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
(4) Optical configuration
18/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
(4) Optical configuration
19/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
(4) Optical configuration
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Technical Background
Suspended 4m RSE
21/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
22/28Keiko Kokeyama 23 July 2010 @ Friday Science
Design sensitivity of CLIO
23/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
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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
25/28Keiko Kokeyama 23 July 2010 @ Friday Science
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.
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Reduction of Mirror Thermo-Elastic Noise
CLIO has finally demonstrated the reduction of the thermal noise on sapphire mirrors around 200 Hz
27/28Keiko Kokeyama 23 July 2010 @ Friday Science
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
28/28Keiko Kokeyama 23 July 2010 @ Friday Science
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