TAMA300

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• Once per 3 years (IVC15)
• 16 parallel sessions (6days)
• Poster sessions (3days)
• Vacuum equipment exhibition (3days)
• Many cancels from Japan
• Few Japanese tourists in the street

• My interest
• Equipment technology
• (TMP, MBP, IP, SRG)
• Coating (DLC, TiN)
• Gas dynamics

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Direct Measurement of Residual Gas Effect on the
sensitivity in TAMA300

• R. Takahashi, Y. Saito, M. Fukushima, M. Ando, K.
  Arai,
• D. Tatsumi, G. Heinzel, S. Moriwaki, and T.
  Yamazaki
• National Astronomical Observatory of Japan, KEK,
  The Univ. of Tokyo

• Vacuum system of TAMA300
• Residual Gas Effect
• Experimental Setup
• Experimental Result
• Discussion
• Summary

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Specification of TAMA300

• Location Mitaka Campus of NAOJ
• Aimed sensitivity h 3x10-21 _at_300Hz
• Baseline length 300m
• Interferometer Fabry-Perot Michelson
• Finesse of Cavity 520
• Laser Injection-lock NdYAG
• Output10W
• l1,064nm
• Recycling Gain 10
• Vacuum System 10-6Pa

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Vacuum System of TAMA300
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Vacuum System of TAMA300

• Large-scale Vacuum System
• Volume 85m3
• Surface 820m2
• Technique
• 6 stainless steel and 2 pure titanium chambers
• ECB(Electro-chemical buffing) process
• Gate valve(400f) with optical window
• Pressure under operating
• Duct 2 x 10-8 Torr Non-baking!
• Chamber 1 x 10-7 Torr

300m long vacuum duct (400mm in diameter)
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Residual Gas Effect 1

• Optical path difference due to fluctuation of
  refractive index
• Correlation function
• Its Fourier transfer

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Residual Gas Effect 2

• Refractive index and Molecular density
• Lorentz-Lorenz formula
• Molecular density
• Correlation function
• Interaction time
• Molecular velocity
• Gaussian beam size
• Correlation function

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Residual Gas Effect 3

• Resulting displacement noise in the
  interferometer
• roundtrip in arm
• dependent in molecular
• We selected Xe-gas.

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Experimental Setup

• Measurement of pressure
• Pressures were measured at 7 points using
  penning gauges.
• Spinning Rotor Gauge (SRG) is suitable for this
  experiment.
• Penning gauges were calibrated by SRG.
• Experiment procedure
• 1. Start ventilation
• 2. Stop ventilation
• 3. Wait for about 20 min.
• 4. Measure pressure, temperature, and noise
• 5. Repeat

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Experimental Result 1

• Measured spectrum
• Most sensitive frequency was about 900Hz.

The Xe-gas pressure of 0.03Pa induced an increase
in the displacement noise of 3x10-18m/Hz1/2
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Experimental Result 2

• Relation between pressure and observed noise
• Observed noise (dx2) was proportional to
  pressure.
• This result is proving the theory.

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Discussion

• Correlation factor
• Observed noise was grater than the calculation
  by factor 2.
• This shows the correlation is larger than the
  assumption because a space is enclosed by the
  tube.
• Acoustic effect
• Mirrors might be directly excited by an acoustic
  emission through low vacuum.
• Environmental acoustic noise is less than 80dB
  (0.2Pa) in TAMA300 facility.
• Maximum 6x10-20m/Hz-1/2 _at_1Pa is predicted.
• (even if the wall of the vacuum chamber did not
  protect any acoustic emission.)
• This effect was negligible.

x1.8
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Summary

• Residual gas effect was measured directly on the
  sensitivity in TAMA300.
• It is found that the Xe-gas pressure of 0.03Pa
  induces an increase in the displacement noise of
  3x10-18m/Hz1/2.
• This noise level is consistent with a calculated
  optical path fluctuation due to residual-gas
  within factor 2.