Cryogenic Underground

Cryogenic

• Cryogenic

• Underground

• Resonant Sideband Extraction (RSE) interferometer

BNS range 158 Mpc, BBH(30Msun) range 1.0 Gpc

• BNS range 158 Mpc, BBH(30Msun) range 1.0 Gpc

Not better even with cryogenic and underground

• Not better even with cryogenic and underground

Basically low, thanks to underground and tower suspensions

• Basically low, thanks to underground and tower suspensions

Cryogenic temperature high Q (low loss) sapphire reduces thermal noise

• Cryogenic temperature high Q (low loss) sapphire reduces thermal noise

• Thick sapphire fibers to extract heat increase suspension thermal noise

• Smaller beam sizes because of smaller mirrors increase coating thermal noise

23 kg mirror was the largest sapphire mirror we can get (aLIGO: 40 kg, AdVirgo: 42 kg)

• 23 kg mirror was the largest sapphire mirror we can get (aLIGO: 40 kg, AdVirgo: 42 kg)

• Smaller mirror increases radiation pressure noise

• Less laser power because of limited heat extraction increases shot noise Intra-cavity power KAGRA: 400 kW, aLIGO/AdVirgo: 700 kW

Increase the mass - GAST project (upto 30 cm dia. ?) - composite mass - A-axis sapphire (upto 50 kg, 26 cm dia.) - non-cylindrical mass (upto 30 kg) - go silicon (upto 200 kg, 45 cm dia.)

• Increase the mass - GAST project (upto 30 cm dia. ?) - composite mass - A-axis sapphire (upto 50 kg, 26 cm dia.) - non-cylindrical mass (upto 30 kg) - go silicon (upto 200 kg, 45 cm dia.)

• Frequency dependent squeezing (Filter cavity) - effectively increase mass and laser power

• Better coating, low absorption mirror

• Better cryogenic suspension design

• ETM different from ITM, half-cryogenic, delay-line, folded arms, higher-order modes, suspension point interferometer …… ???

We need a plan to integrate these ideas

• We need a plan to integrate these ideas

• To begin with, some example plans were proposed

• Plan: Blue (by Yutaro Enomoto) use heavier sapphire mirrors

• Plan: Black (by Kentaro Komori) use silicon mirrors

• Plan: Brown (by Koji Nagano) lower the power to focus on low frequency

• Plan: Red (by Sadakazu Haino) increase the power to focus on high frequency

Heavier sapphire and heavier IM, 20 K

• Heavier sapphire and heavier IM, 20 K

Silicon 123 K, 1550 nm, radiative cooling

• Silicon 123 K, 1550 nm, radiative cooling

Same test mass, low power, high detuning, 20 K

• Same test mass, low power, high detuning, 20 K

Same test mass, high power, 24 K

• Same test mass, high power, 24 K

Also feasibility study necessary

• Also feasibility study necessary

Science case discussion is necessary

• Science case discussion is necessary

What is the best figure of merit to compare the plans? - Sensitivity curve (with error bars)? - Inspiral range? What mass? - Event rate (with error bars)? - Parameter estimation accuracy?

• What is the best figure of merit to compare the plans? - Sensitivity curve (with error bars)? - Inspiral range? What mass? - Event rate (with error bars)? - Parameter estimation accuracy?

• Broadband or narrowband in high event rate regime by aLIGO + AdVirgo? - Does 4th detector help parameter estimation?

• What about real 3G detector (~10 km class)? - Asia-Australian 8-km detector? - Where?

Many ideas for improving the sensitivity have been proposed, and some R&D are on going

• Many ideas for improving the sensitivity have been proposed, and some R&D are on going

• Sensitivity design study on future KAGRA upgrade to integrate these ideas is necessary

• There are some example plans

• Need more serious discussion based on science, feasibility, budget and timeline

• Any comments? New ideas?

Optical parameters - Mirror transmission: 0.4 % for ITM, 10 % for PRM, 15.36 % for SRM - Power at BS: 780 W - Detune phase: 3.5 deg (DRSE case) - Homodyne phase: 133 deg (DRSE case)

• Optical parameters - Mirror transmission: 0.4 % for ITM, 10 % for PRM, 15.36 % for SRM - Power at BS: 780 W - Detune phase: 3.5 deg (DRSE case) - Homodyne phase: 133 deg (DRSE case)

• Sapphire mirror parameters - TM size: 220 mm dia., 150 mm thick - TM mass: 22.8 kg - TM temperature: 21.5 K - Beam radius at ITM: 3.5 cm - Beam radius at ETM: 3.5 cm - Q of mirror substrate: 1e8 - Coating: tantala/silica - Coating loss angle: 3e-4 for silica, 5e-4 for tantala - Number of layers: 9 for ITM, 18 for ETM - Coating absorption: 0.5 ppm - Substrate absorption: 20 ppm/cm

• Suspension parameters - TM-IM fiber: 35 cm long, 1.6 mm dia. - IM temperature: 16.3 K - Heat extraction: 6580 W/m/K - Loss angle: 5e-6/2e-7/7e-7 for CuBe fiber?/sapphire fiber/sapphire blade

• Inspiral range calculation - SNR=8, fmin=10 Hz, sky average constant 0.442478

• Seismic noise curve includes vertical coupling, vibration from heatlinks and Newtonian noise from surface and bulk

Measured v = 0.5~2 m/s → seems OK

• Measured v = 0.5~2 m/s → seems OK