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Low frequency anti-vibration system of LCGT

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),

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Low frequency anti-vibration system of LCGT

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  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

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

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

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

  7. Simulation • 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)

  8. Type-A Point Mass Model Type-B Type-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

  12. Damping of torsion mode (Type-A) • 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. A disc is suspended from the top filter. Permanent magnets attached to the disc damp the motion of filter 1 by eddy current.

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

  14. Rigid body model Type-B • 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.

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

  16. Transfer function (Type-B)

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

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

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

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

  21. Design & Testa. Pre-isolator Assembling at G&M (May, 2011) 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)

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

  23. Design & Testc. Payload

  24. Design & Testd. Outer frame Preliminarily Pre-isolator and Support structure at ICRR (Aug, 2011) Bending mode (2nd)Torsion mode

  25. Schedule First operation

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