Status of LCGT and CLIO Masatake Ohashi (ICRR, The University of TOKYO) and LCGT, CLIO collaborators TAUP2007 Sendai, Japan 2007/9/12

TAUP 2007 Sendai Japan 2007/09/12 Contents LCGT Outline Status of LCGT –Interferometer Design –Sapphire Mirror and its Suspension –Cryostat and Cooling Technique Status of CLIO –Present Status as a proto-type of LCGT Summary

TAUP 2007 Sendai Japan 2007/09/12 illustration: KAGAYA Large-scale Cryogenic Gravitational wave Telescope （ LCGT ） 180Mpc

TAUP 2007 Sendai Japan 2007/09/12 LCGT Outline It is 3km Fabry-Perot interferometer with power recycling and broadband RSE. Main mirrors made of sapphire are cooled at 20K. It is built at underground site in Kamioka Mine. Two independent interferometers are installed. The main target is the coalescence of Binary Neutron Star ｓ at 180Mpc.

TAUP 2007 Sendai Japan 2007/09/12 LCGT on LIGO Web Next generation IFO from Japan

TAUP 2007 Sendai Japan 2007/09/12 Merit of Underground site Quiet ! Seismic activity of city area Seismic activity of Kamioka Mine The point is that at least 100m below land surface is necessary to prevent wind effect.

TAUP 2007 Sendai Japan 2007/09/12 Interferometer Design

TAUP 2007 Sendai Japan 2007/09/12 Interferometer Design - Over View 1 - Detector parameters Laser Nd:YAG laser (1064nm) Injection lock + MOPA Power :150 W Main Interferometer Broad band RSE configuration Baseline length :3km Beam Radius :3-5cm Arm cavity Finesse : 1550 Power Recycling Gain : 11 Signal Band Gain : 15 Stored Power :771kW Signal band :230Hz Vacuum system Beam duct diameter : 100cm Pressure : Torr Mirror Sapphire substrate + mirror coating Diameter :25cm Thickness :15cm Mass :30 kg Absorption Loss : 20ppm/cm Temperature :20 K Q = 10 8 Loss of coating :10 -4 Final Suspension Suspension + heat link with 4 Sapphire fibers Suspension length :40cm Fiber diameter :1.5mm Temperature :16K Q of final suspension : 10 8

TAUP 2007 Sendai Japan 2007/09/12 Interferometer Design - Over View 2 - Main IFO : 3km IFO Input optics : Two MCs, Modulators, MMT Output optics: OMC, Photo detectors

TAUP 2007 Sendai Japan 2007/09/12 Interferometer Design - Layout 1 - Center room for IFO-1 Center room for IFO-2 3km arm Two IFOs share the vacuum pipes

TAUP 2007 Sendai Japan 2007/09/12 Interferometer Design - RSE - Merit of RSE High-finesse cavity and moderate PRG Easier to realize high power in cavities Smaller transmission light in optics Flexible optimization for GW sources Independent adjustment of power in cavities and signal band Narrow-band observation (optional) Main reason for LCGT Absorption in sapphire substrates Heat absorption : 20ppm/cm x 15 cm = 300 ppm Cooling power : 1W for each mirror Laser power on BS should be less than ~1kW (safety factor 3)

TAUP 2007 Sendai Japan 2007/09/12 Sapphire Mirror

TAUP 2007 Sendai Japan 2007/09/12 Sapphire Mirror - Absorption - Laser light absorption is important factor for cooling. LCGT requirement : substrate 20ppm/cm (-> 250mW) coating 1ppm (-> 40mW) We need high quality sapphire substrate.

TAUP 2007 Sendai Japan 2007/09/12 Sapphire Mirror - Mechanical Quality Factor - Over 10 8 is obtained

TAUP 2007 Sendai Japan 2007/09/12 Sapphire Mirror - Dissipation of the Coating film - Loss Angle Temperature [K] Dissipation is almost independent of Temperature

TAUP 2007 Sendai Japan 2007/09/12 Sapphire Mirror - Thermal Expansion - Thermal expansion is negligible at cryogenic temperature. Thermal Expansion Temperature [K]

TAUP 2007 Sendai Japan 2007/09/12 Cryogenic Techniques

TAUP 2007 Sendai Japan 2007/09/12 Cryogenic Technique - Estimated Heat Generation in the Mirror - T=20 K q=290 mW ・ Design Safety factor Mirror substrate : Sapphire Suspension rods : Sapphire

TAUP 2007 Sendai Japan 2007/09/12 Cooling method by a cryocooler

TAUP 2007 Sendai Japan 2007/09/12 Seismic Noise Attenuation

TAUP 2007 Sendai Japan 2007/09/12 Seismic Attenuation System (SAS) Inverted pendulum –30mHz 3 cascaded GAS filter –500mHz Test mass suspension –triple pendulum

TAUP 2007 Sendai Japan 2007/09/12 Suspension Point Interferometer (SPI) - Background and Purpose -

TAUP 2007 Sendai Japan 2007/09/12 Schedule and Budget LCGT proposal is submitted to the Ministry of Education and Science （ MEXT) as one of recommended projects of the University of TOKYO. But LCGT will not start at M$ without salary and maintenance We will retry next year

TAUP 2007 Sendai Japan 2007/09/12 CLIO

TAUP 2007 Sendai Japan 2007/09/12 Cryogenic prototype for LCGT

TAUP 2007 Sendai Japan 2007/09/12 Overview of CLIO

TAUP 2007 Sendai Japan 2007/09/12 Cryostat for an end mirror

TAUP 2007 Sendai Japan 2007/09/12 8.8K 45K 63K 12.9K Cooling test and achieved temperature

TAUP 2007 Sendai Japan 2007/09/12 Cooling summary Cooling time Mirror temp Heat in the suspension Heat at the 1st cooling 2006/02 Inline end 176hour start 07/06/22,10: K40mWN/A Inline near 174hour start 07/06/22,10: K36mWN/A Per arm end 164hour start 07/04/27,11: K62mW #1 116mW Per arm near 193hour start 07/08/16,12: K29mW109mW #1; No shield for radiation from the outer shield at 63K.

TAUP 2007 Sendai Japan 2007/09/12 Low vibration PT refrigerator by KEK and SUMITOMO

TAUP 2007 Sendai Japan 2007/09/12 Cryogenic suspension

TAUP 2007 Sendai Japan 2007/09/12 Heat Transfer Radiation shield (40K) Mirror (20K) 300K Radiation ( straying ) 300K Radiation from window of Gate Valve warms mirrors Serious Problem for cooling Good Heat Transfer, Baffles, … Gate Valve (300K)

TAUP 2007 Sendai Japan 2007/09/12 Radiation Shields

TAUP 2007 Sendai Japan 2007/09/12 Cooling procedure Cooling shortens suspension by 2mm STEP1 cooling mirror alignment STEP4 cooling mirror alignment STEP2 cooling mirror alignment STEP3 cooling mirror alignment

TAUP 2007 Sendai Japan 2007/09/12 Expected Noise Spectrum at 20K Current best (300K) Target sensitivity (300K) Target sensitivity (20K) Resonance of suspension system

TAUP 2007 Sendai Japan 2007/09/12 Noise budget for CLIO (300K) Cooling

TAUP 2007 Sendai Japan 2007/09/12 YES ! Thermal Noise of Aluminum Wires Thermal noise reduced by cooling ?

TAUP 2007 Sendai Japan 2007/09/12 CLIO Stability Akutsu’s POSTER

TAUP 2007 Sendai Japan 2007/09/12 SUMMARY We will submit LCGT budget request for FY2009 again next year. Cryogenic prototype CLIO was completed. Now in commissioning phase. We demonstrated to operate interferometer with cryogenic mirrors, but careful heat transfer is necessary for cooling.

TAUP 2007 Sendai Japan 2007/09/12 European Plan

TAUP 2007 Sendai Japan 2007/09/12 Interferometer Design - Layout 2 - Baffle for LCGT Specification of LCGT Tube diameter1000mm Mirror diameter250mm Mirror distance600mm Mirror offset340mm Seismic motion1 x m/Hz Estimated scattered light noise 4.2 x m/Hz (Safety factor=7) 1/10 45 (for one mirror) Integration Each reflection Baffle design Number:45x2for one arm Height:35~50mm Surface:DLC coatings Diamond-Like Carbon (DLC) coatings Surface roughness: Ra=20nm Outgassing: lower than SS316 with baking Reflectivity: 5% for p-polarization at45deg.