Advances in Passive Seismic Attenuation Systems

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Advances in Passive Seismic Attenuation Systems

• Maddalena Mantovani
• Anamaria Effler
• Riccardo DeSalvo

2
Activities

• Got some better understanding of Maraging
  dissipation properties, wrote paper
• Studying seismic attenuation starting _at_ 1 Hz for
  low frequency underground interferometers to
  complement NN depression and subtraction
  techniques
• Comparing Maraging, CuBe, and possibly metglass
  dissipation behavior.

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Requirements

• The Requirements for he underground ifo. are
  attenuation of 1000 at 5 Hz for multi ton
  payloads
• Passive Horizontal attenuation is trivial
• Vertical must drive MGAS to lower frequency
• Refine mechanical tuning
• Add electromagnetic (LVDT, op-amp, voice coil)
  springs in parallel to fine tune the resonant
  frequency and compensate thermal drifts

4
Means

• Used a two blade prototype for the Maraging paper
• Using old demo unit for developing
  electromagnetic springs and measuring transfer
  function (50 Kg payload)
• Using the Deep Fall Back Solution prototype to
  demonstrate the multi-ton capabilities
• Using LCGT blades to compare materials

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Results (Maraging dissipation properties)

• Paper
• " Study of Quality Factor and Hysteresis
  Associated with the State-of-the-art Passive
  Seismic Isolation System for Gravitational Wave
  Interferometeric Detectors".
• The draft is available at http//www.ligo.caltech.
  edu/htariq/ric/maraging_hysteresisLRP.pdf

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Setup used for the paper
Click on image to start movie (15 sec)

• The two cantilevers support the payload and,
  individually would have high resonant frequency.
• The frequency is lowered by radially compressing
  the two springs one against the other, the two
  arches form an antispring that neutralize the
  cantilever springiness and the resonant frequency
  can be tuned at will

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Results (Old demo unit)

• Instrumented with the LVDT and Voice Coil.
• Built the OpAmp coil driver circuit
• Driven the spring to 300 mHz fully passively
• Driven the spring to 70 mHz (attenuation 200 at 1
  Hz) with electromagnetic spring, going down
• Studying Q factor versus frequency and found
  expected quadratic behavior with frequency,
  pointing at Q0 for f0

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seconds
seconds
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Q t n
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Work in course (Old demo unit)

• Further Reducing the resonant frequency
• Ready to measure attenuation transfer functions
  (see movies)
• Low frequency measurements take time, progress is
  slow

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This is exciting the payload (hanging
below) Click on image to start movie (15 sec)
Load support Disk Suspension Wire Payload 50
Kg
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And this is how we measure the transfer function,
shake the body and measure stability of
payload Click on image to start movie (15 sec)
Load support Disk (stationary) Shaking
Body Support Susp. wire Payload
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Progress with DFBS prototype

• This prototype was built and minimally tested 1.5
  years ago as a fall back solution to be mounted
  on piers in case HEPI failed
• It was then mothballed
• It comprises two blades out of 12 for a complete
  pier system
• It is used to demonstrate multi-ton, low
  frequency payload capabilities
• Payload 350 Kg on 2 blades

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DFBS prototype
Bellow equivalent springs Cantilevers 350
Kg Payload
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LIGO Bellow springs
Blade Nose bolting
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Progress with DFBS prototype

• Did not remove bellow springs in parallel because
  of geometry constraints of this prototype
• Made tests in full, pier compatible configuration

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Progress with DFBS prototype

• So far driven down to 120 mHz despite the
  additional springs (4/3 of the equivalent bellow
  stiffness) in fully passive configuration
• (Attenuation of 50 _at_ 1 Hz)
• Expect 30 mHz if tuned with e.m. spring
• Transfer function will not be possible on this
  prototype, we would need hydraulics to excite the
  frame
• Proven on preceding prototypes that attenuation
  plateau at 1000, fully expect same performance

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LIGOBellow Equivalent Springs (2x)
Frequency Tuning Compression screws
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300 mHz tune
Click on image to start movie (15 sec)
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300 mHz tune
Click on image to start movie (15 sec)
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200 mHz tune
Click on image to start movie (15 sec)
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150 mHz tune
Click on image to start movie (15 sec)
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DFBS performance

• Estimated attenuation of
• gt70 _at_ 1Hz and above in fully passive
  configuration
• 1000 _at_ 4 Hz fully passive configuration
• 1000 _at_ 1 Hz semi-passive, with e.m. spring
• Upgradeable to gtgt 1000 _at_ 1 Hz with accelerometers
  and active feed back
• Underground interferometer specs satisfiable!
• Natural damping makes damping unnecessary in the
  vertical direction

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Materials comparisons

• Mounted Maraging blade
• Starting measurements
• Twin CuBe spring ready
• Waiting for Metglas material