1. Large-scale Cryogenic Gravitational- wave Telescope, LCGT Keiko Kokeyama University of Birmingham 23 rd July 2010 Friday Science

2. 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 0/28 Keiko 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”

3. 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 relativity  The GW astronomy  Experimental verification of the general relativity  The GW astronomy 1/28 Keiko Kokeyama 23 July 2010 @ Friday Science

4. Gravitational Wave Detectors Super accurate measurement to detect 10 -20 m change per 1 m Bright Dark Photo detector Beam- splitter Laser 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 2/28 Keiko Kokeyama 23 July 2010 @ Friday Science

5. GEO600 VIRGO TAMA300 LIGO Upgrading to the 2 nd Generation Detectors Advanced LIGO, Advanced VIRGO, GEO HF, LCGT The 1 st Generation Detectors Large Scale ground-based GW detectors 3/28 Keiko Kokeyama 23 July 2010 @ Friday Science

6. On 22 nd 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 3 rd year. The result will be appear in August. 4/28 Keiko Kokeyama 23 July 2010 @ Friday Science

7. 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 5/28 Keiko Kokeyama 23 July 2010 @ Friday Science

8. GW detector network  LCGT plays a role of Asia-Oceania center among other detectors Best sensitivity direction for LCGT LIGO Hanford LIGO Livingston VIRGO 6/28 Keiko Kokeyama 23 July 2010 @ Friday Science The good-sensitivity directions are complementary for other detectors

9. (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 7/28 Keiko Kokeyama 23 July 2010 @ Friday Science

10. (1) Underground Site 8/28 Keiko Kokeyama 23 July 2010 @ Friday Science

11. (1) Underground Site 9/28 Keiko Kokeyama 23 July 2010 @ Friday Science

12. (1) Underground Site 10/28 Keiko Kokeyama 23 July 2010 @ Friday Science

13. 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 11/28 Keiko Kokeyama 23 July 2010 @ Friday Science

14. (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 12/28 Keiko 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.

15. ↓ 2-stage suspension (Low temperature) (2) Seismic isolation system 13/28 Keiko Kokeyama 23 July 2010 @ Friday Science 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

16. (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 14/28 Keiko Kokeyama 23 July 2010 @ Friday Science

17. 8K, 100K Heat link 1W, 5 ×  3mm Al Heat link 1W, 7 ×  1mm, Al SAS, 300 K 20K 10K Sapphire wire, 860 mW 40cm,  1.8mm Bolfur wire 40cm,  1.8mm Recoil Masses will be suspended by Sapphire 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) 15/28 Keiko Kokeyama 23 July 2010 @ Friday Science

18. (4) Optical configuration Main IFO 16/28 Keiko Kokeyama 23 July 2010 @ Friday Science

19. Main IFO Resonant-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 SEC PRC (4) Optical configuration 17/28 Keiko Kokeyama 23 July 2010 @ Friday Science

20. 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 18/28 Keiko Kokeyama 23 July 2010 @ Friday Science PRC SEC FP

21. 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 19/28 Keiko Kokeyama 23 July 2010 @ Friday Science

22. 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 20/28 Keiko Kokeyama 23 July 2010 @ Friday Science

23. Technical Background Suspended 4m RSE 21/28 Keiko Kokeyama 23 July 2010 @ Friday Science

24. 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 Fabry-Perot cavity Beam-splitter Fabry-Perot cavity 22/28 Keiko Kokeyama 23 July 2010 @ Friday Science

25. Design sensitivity of CLIO 23/28 Keiko Kokeyama 23 July 2010 @ Friday Science

26.  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 suspended sapphire mirror (  100×60, 2kg) 6-stage vibration isolation (3 stages in 300K, 3 stages in cryogenic) Cryogenic in CLIO 24/28 Keiko Kokeyama 23 July 2010 @ Friday Science

27. 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 25/28 Keiko Kokeyama 23 July 2010 @ Friday Science

28. 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. 26/28 Keiko Kokeyama 23 July 2010 @ Friday Science

29. Reduction of Mirror Thermo-Elastic Noise CLIO has finally demonstrated the reduction of the thermal noise on sapphire mirrors around 200 Hz 27/28 Keiko Kokeyama 23 July 2010 @ Friday Science

30. 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 28/28 Keiko Kokeyama 23 July 2010 @ Friday Science

31. End

32. Supplement slide (1) Wave length1064 Initial Laser Power 150 Injecting Laser Power into IFO 78.48 (in total), 75 (carrier) Modulation depth 0.3 for both RF freq 111.25M (PM) RF freq 245.00M (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 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 length25 m SR cavity length 73.2826 m SRC detuning phase 86.5 3.4 ???

33. EM mass30 FM mass30 PRM mass TBD SRM mass TBD BS mass TBD EM ROC7113.900 m FM ROC7113.900 m FM AR ROC TBD PRM ROC TBD SRM ROC TBD BS ROCInfinity EM radius/thickn ess 25 / 15 cm FM radius/thickn ess 25 / 15 cm PRM radius/thickn ess TBD SRM radius/thickn ess TBD BS radius/thickn ess TBD EM Reflectivity 0.999945 FM Reflectivity 0.996 PRM Reflectivity 0.9 SRM Reflectivity 0.8464 = 0.92 2 BS Reflectivity 0.5 HR Coating Loss of EM, FM, PRM and SRM 45e-6 BS Loss100e-6 Transmissivit y 1 - R - Loss AR Transmissivit y 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 length1.5 m OMC Finesse2000 OMC input/output mirror reflectivity TBD OMC end mirror reflectivity TBD OMC MC FSR??? DC readout phase 134.7 deg121.8d 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 radius3 cm Suspension length40 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 radius12.5 cm Mirror thickness15 cm Bulk absorption20 ppm/cm Coating absorption0.1 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 4e11Pa Density of Sapphire 4e3kg/m^3 Poisson ratio of Sapphire 0.29 Thermal expansion of Sapphire (20K) 5.6e-91/K Specific heat of Sapphire (20K) 0.69J/K/kg Thermal conductivity of Sapphire (20K) 1.57e4W/m/K Thermal expansion of Sapphire (300K) 5.0e-61/K Specific heat of Sapphire (300K) 790J/K/kg Thermal conductivity of Sapphire (300K) 40W/m/K Young's modulus of Silica 7.2e10Pa Poisson ratio of Silica 0.17 Refraction index of Silica 1.45 Thermal expansion of Silica (300K) 5.1e-71/K Specific heat per volume of Silica (300K) 1.64e6J/K/m^3 Thermal conductivity of Silica (300K) 1.38W/m/K dn/dT of Silica (300K) 8e-61/K Young's modulus of Tantala 1.4e11Pa Poisson ratio of Tantala 0.23 Refraction index of Tantala 2.06 Thermal expansion of Tantala (300K) 3.6e-71/K Specific heat per volume of Tantala (300K) 2.1e6J/K/m^3 Thermal conductivity of Tantala (300K) 33W/m/K dn/dT of Tantala (300K) 14e-61/K

34. Suppliment slide (3)

35. Reduction of Suspension Thermal Noise Suppliment slide (3)

36. Vacuum tanks Vacuum level 2 x 10 -7 Pa Vacuum duct 3km length 1m diameter steinless steel