1. Low frequency anti-vibration system of LCGT Vibration Isolation Group R. Takahashi (ICRR), K. Yamamoto (ICRR), T. Uchiyama (ICRR), T. Sekiguchi (ICRR), H. Ishizaki (NAOJ), A. Takamori (ERI), R. DeSalvo (Univ. of Sannio), E. Majorana (INFN), J. van den Brand (NIKHEF), E. Hennes (NIKHEF), A. Bertolini (AEI/NIKHEF) EGO-ICRR Meeting (5 October, 2011)

2. Disposition of vibration isolation system

3. Type-A: IP + GASF (5 stage) + Payload (23kg, cryogenic) Type-B: IP + GASF (3 stage) + Payload (10kg/20kg, room temp.) Type-C: Stack + Single/Double-pendulum (~1kg) Configuration ChamberiLCGTbLCGT ITMX, ITMY, ETMX, ETMY Type-A IAOX, IAOY, EAOX, EAOY Type-B Payload on Stack (for ITM/ETM) Type-C (for AO) BS, PRM, PR2, PR3, SRM, SR2, SR3 Type-B Payload on StackType-B MCF, MCE, MMT, PDType-C

4. Type-A (2-layer structure) Upper tunnel containing pre- isolator (short IP and Top filter) Upper tunnel containing pre- isolator (short IP and Top filter) 1.2m diameter 5m tall borehole containing standard filter chain 1.2m diameter 5m tall borehole containing standard filter chain Lower tunnel containing cryostat and payload Lower tunnel containing cryostat and payload

5. Type-B IP base is supported by the outer frame. IP base is supported by the outer frame. Suspended/On-stack table is used for small optics. Suspended/On-stack table is used for small optics. Pre-isolator is the same as Type-A’s. Pre-isolator is the same as Type-A’s. Inverted pendulum Top filter 2-stage GASF Mirror

6. Type-C Stack is based on TAMA’s design. Stack is based on TAMA’s design. Rubber for stack is enclosed by bellows. Rubber for stack is enclosed by bellows. Differential evacuation is necessary for the bellows. Differential evacuation is necessary for the bellows.

7. Model calculation has been developed with design works. Longitudinal mode by point mass model (R. Takahashi) Torsion mode by point momentum-of-inertial model (T. Sekiguchi) Full dimensional mode by rigid body model (T. Sekiguchi & E. Majorana) Simulation

8. Type-A Point Mass Model Type-BType-C (Filter4)

9. Displacement of test mass The isolation above 2Hz is due to the heat link of 0.03Hz. The 1% coupling from vertical displacement is comparable with the horizontal one. Predicted displacements are consistent with the IFO noise budget above 5Hz.

10. Displacement of each mirror Calculation for the Type-B system does not contain the effects due to the support structure for the IP. Almost main optics are suspended by the Type-B payload on the stack in iLCGT.

11. Requirements & Prediction iLCGTbLCGT TargetCalculationRequirementCalculation Displacement @10Hz [m/rHz] →3 x 10 -17 4 x 10 -20 RMS (velocity) [μm/s] →3.10.10.08 RMS (displace.) [μm] →2.20.10.05

12. A disc is suspended from the top filter. A disc is suspended from the top filter. Permanent magnets attached to the disc damp the motion of filter 1 by eddy current. Permanent magnets attached to the disc damp the motion of filter 1 by eddy current. The motions of filter 2~4 are also damped, if the torsion stiffness of each wire is optimal. We need to optimize damping strength & torsion stiffness of every wires. Damping of torsion mode (Type-A)

13. Yaw motion of mirror The transfer function shows good damping.

14. Rigid body model Each body has 6 DOF (X, Y, Z, θx, θy, θz). Wire potential is divided into stretches and torsions. GAS works as a one-dimensional ideal spring. Elasticity of the heat links is taken into account. No deformation of the bodies, no violin motions of the wires. Type-B

15. Torsion(.012Hz)Torsion(.020Hz)IP Trans.(.030Hz)IP Long.(.030Hz) Vertical(.239Hz)Torsion(.032Hz)IP Yaw(.051Hz)Roll(.403Hz)

16. Transfer function (Type-B)

17. Displacement of mirror (Type-B) Displacement [m/rHz]

18. Angular motion of mirror Room temp. Cryogenic vibration Heat links Monte Carlo simulation within the following asymmetries. Wire length ： ±0.5 mm Wire length ： ±0.5 mm Suspension point ： ±0.5 mm for x, y, z Suspension point ： ±0.5 mm for x, y, z Effective stiffness of the inverted pendulums ： ±50 % Effective stiffness of the inverted pendulums ： ±50 % Anchor point of the heat link ： ±5 cm Anchor point of the heat link ： ±5 cm

19. Angular Fluctuation of Mirror (Type-A) Pitch Yaw Anchor point of heat links, asymmetry in IPs Asymmetry in wire lengths/suspension points

20. Impact to the Sensitivity (Type-A) The effect due to the angular motion is relatively small except some resonance peaks. Pitch resonance peak 1 mm

21. Design & Test a. Pre-isolator GAS blades (A), Horizontal accelerometers (B), Central keystone (C), Motor controlled rotation mechanism (D), Platform for vertical accelerometer (E), Coaxial LVDT and voice coil actuator (F), Motor driven vertical springs (G), Sliding clamps (H), Special tool tuning filter resonant frequency (I), Counterweights for GASF (J), Inverted pendulum legs (K), Magnetic dampers (L), Counterweights for inverted pendulum (M), Motor driven horizontal springs (N), Horizontal LVDT (O), Horizontal voice coil actuators (P), and Hooking points of magnetic damper (Q) Assembling at G&M (May, 2011)

22. Design & Test b. Standard GASF Measured transfer function at NIKHEF (Feb, 2011) Actuator LVDT Magic wand

23. Design & Test c. Payload

24. Design & Test d. Outer frame Bending mode (2 nd ) Torsion mode ModeFEM Calc. [Hz] Meas. [Hz] Bending 1 st 7.121.1 Bending 2 nd 78.839.6/48.3 Torsion17.343.8 Pre-isolator and Support structure at ICRR (Aug, 2011) Preliminarily

25. Schedule 201120122013201420152016 Standard GASFPrototype test in NIKEF & ICRR Procure Assembling Pre-isolatorPrototype test in ICRR Procure Assembling Type-B payloadPrototype test in NAOJ Procure Assembling Installation Type-A SASPrototype test in the site Installation Type-B SASPrototype test in TAMA Installation StackProcure Installation First operation