Improvement of Vibration Isolation system for TAMA300

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Improvement of Vibration Isolation system for
TAMA300

• R. Takahashi, K. Arai, and the TAMA collaboration
• NAOJ, ICRR, The Univ. of Tokyo, ILS, KEK, MUE,
• The Univ. of Osaka, and YITP

• Structure of Vibration Isolation System
• Modification of Suspension System
• Active Control System
• RMS Amplitude
• Stability of Interferometer
• Summary

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Structure of Vibration Isolation System

• Requirement
• Isolation gt 108
• 3-layers Stack
• Enclosed rubber by bellows
• Double Pendulum
• Flexible eddy current damping
• Active Control
• Pneumatic actuator

Tokkyokiki Corp. a2
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Modification of Suspension System

• Large Pitch mode resonance
• Removed frequency from 5Hz to 1Hz
• Reduced RMS from 4mrad to 0.8mrad
• Decreasing UGF of alignment control
• Improved sensitivity around 100Hz

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Estimated Seismic Noise

• Sensitivity of TAMA300
• Seismic noise is dominant at lt 30Hz
• Alignment noise is dominant at gt 30Hz
• Coupling from Vertical mode is larger than
  Horizontal mode
• 10-16m/Hz1/2 at 40Hz

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Installation of Active Control

• Compact built-in type unit
• Disposition 3 legs ? 4 units
• Keeping Stack and Suspension setup 1,500kg
• Mechanical resonance around 100Hz notch filters
  by DSP

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Beam axis
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Control Loop

• Absolute Vibration Feedback Loop 1 - 20Hz
• Ground Vibration Feed-forward Loop 0.5 - 50Hz
• Position Feedback Loop DC - 0.1Hz

Customization by programming DSP
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Transfer functions

• Resonant frequency without control
• X9Hz
• Y9Hz
• Z5Hz
• Controlled isolation ratio
• 10 - 20dB at gt 1Hz

Frequency Hz
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RMS Amplitude of Seismic Vibration

• Ground vibration (1-10Hz)
• Day time(917) 5 - 10 mgal
• Night time(188) 2 - 5 mgal
• With active control lt 2 mgal

Sunday
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Stability of Interferometer

• Full-time observation
• Over 24-hours operation without unlock was
  realized in a test run.

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Summary

• Mirror suspension system was modified. Since
  large resonance disappeared, an alignment control
  with low UGF was realized.
• Seismic noise is not dominant at gt 30Hz in the
  present sensitivity of TAMA300.
• Isolation ratio of 10 - 20dB was obtained with
  Active Control using pneumatic actuators.
• RMS amplitude (1-10Hz) of seismic vibration was
  improved from 5 - 10mgal to less than 2mgal by
  Active Control.
• Active Control contributed to realize a
  continuous locking for more than 24 hours.