1. LCGT Technical Review Suspension Point Interferometer for Parasitic Noise Reduction and an Additional IFO S.Miyoki (ICRR, Univ. of TOKYO)

2. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Contents Parasitic noise in LCGT Heat link wires design as both a thermal conductor and a seismic noise isolator Designed thermal conduction and its seismic noise isolation performance SPI performance principle SPI by-product SPI experimental demonstrations Technical issues toward LCGT

3. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo What is Parasitic Noise in LCGT ?

4. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Seismic Noise through the Heat Link Wires - We should find a compromising design of HLWs - Heat that is generated in the sapphire mirrors should be transferred only by the heat conduction of sapphire fibers and the HLWs to the inner Radiation shield at 8K. HLWs, however, introduce the seismic noise to the mirror. - How to decide and what consider about the Heat Link Isolation ? - Trade Off Relation

5. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo How to design the Heat Link Wires (1) The heat that should be transferred is 290 mW @ a near mirror. We set a safety factor over 3, i.e. 1W. (2) We select U- shape HLW because it provides the least spring constant for both horizontal and vertical motion, and the least length for thermal conduction. (3) From the requirement of seismic noise isolation, the least stage number is 6 for horizontal and 5 for vertical. Practically, the allowable stage number in the cryogenic area, however, is two (Mirror, Upper mass) or three (+ suspension platform). (4) In principal, the spring constant of HLW can be reduced by increasing the number of HLW that has less diameter, keeping the required heat transfer ability, because spring constant is proportional to fourth power of a wire diameter. (note : This U shape spring has an isolation plateau because the HLW weight is not negligible. So the excess reduction of the spring constant is nonsense.) (5) Survey the optimum pendulum stage numbers in the cryo- genic area, and HLW diameter, length, number, and corres- ponding spring constant and isolation performance.

6. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Present Heat Link Wire Design Model - 3 stages in the Cryo- area. - 2 cascade of a HL path. - Number of HLW is less than 10.

7. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Estimated Seismic Noise Isolation through HLWs (1) The Vertical- to- horizintal coupling noise is dominant.

8. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo How to Reduce ? LCGT selects SPI

9. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Estimated Seismic Noise Isolation through HLWs (2) Expected SPI reduction : 1/100

10. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo What is SPI ? SPI : proposed by Pro.Drever : forms an another interferometer using the upper masses. Requirement : 1/100

11. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo How it works as an parasitic noise reducer ? (FP cavity)

12. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo How it works as an parasitic noise reducer ? (Michelson Interferometer)

13. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo What dose the SPI contribute to ? (1) SPI reduces any kind of disturbance to the SPI masses including the seismic noise through the HLWs and actuator noise that originates from the electrical circuit noise. The reduction of the actuator noise allows stronger actuating force, which contributes to easier lock acquisition and wider dynamic range. Additionally, the RMS amount for the differential length control will be decreased. (2) SPI could be an another Gravitational Wave detector that has a different observational frequency band using a higher laser Power and SPI mirror substrate.

14. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Experimental Demonstration (1) Y. Aso’s Work PLA 327 (2004) 1-8

15. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Experimental Demonstration (2)

16. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Experimental Demonstration (3) Recoil mass Main mass SPI mass MGAS filter 2 Damping mass Eddy current plate MGAS filter 1 40cm 1m

17. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Experimental Demonstration (4) (Laser, Rigid cavity, Triple Pendulum) Laser Rigid cavity Triple pendulum

18. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Experimental Demonstration (5) (Each mass of the triple pendulum) Upper mass for SPI GAS at the top of Triple pendulum Mirror mass

19. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Experimental Demonstration (6) Displacement of the mirror with and without SPI SPI effect of 1/10~ 1/100 reduction is obtained below 2.5Hz. Above 2.5Hz, however, the vibration of other degree of freedom spoils the SPI effect. with SPI without SPI

20. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Experimental Demonstration (7) Transfer function between the damping mass and the mirror Frequency [Hz] Transfer function [dB] Recently, SPI effect is obtained below 10Hz. Horizontal transfer function from a damping mass(one mass is driven) to the main interferometer 2004 2005 Transfer function [dB] Frequency [Hz] 1 100.1 10 -1 10 -2 10 -3 10 -4 10 -6

21. LCGT Technical Review (2005/8/23) ICRR Univ. of Tokyo Technical Issues toward LCGT - SPI performance as an parasitic noise reduction device is now being evaluated, and displacement noise reduction of about 1/10 ~ 1/100 is obtained below 2.5Hz. Some improvements for the proto- type SPI suspension system to extend the frequency range, where the SPI effect is obtained, are being adopted. - Individual alignment control system between the SPI mirror and the main mirror should be established. - Practical design of the LCGT suspension using sapphire mirror and suspension fiber should be proposed.