Output Mode Cleaner Seismic Attenuation System

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Output Mode CleanerSeismic Attenuation System

• A tentative OMC SAS design has been developed on
  the following assumptions
• The OMC will be housed in a HAM chamber
• Some seismic attenuation is needed
• Some space is needed to house the feeding optics
• The OMC optical bench must be easily aligned, and
  return to the original alignment after
  interventions and must be able to track tidal
  movements. It should be immune to thermal drifts
• Must protect optics from 10 mm earthquakes
• The OMC SAS must be as simple as possible and
  must easily convert to the lower beam line of
  Ad-LIGO

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OMC SAS

• Since we do not know yet the real estate
  requirements of the feeding optics, I thought
  that the most prudent policy is to base the work
  around the present LIGO optical bench geometry
• In any case the cost differential between a large
  and a small seismic attenuation table is marginal
  and there is advantage to work using a table that
  everybody is comfortable with.
• The complexity of handling a small and a large
  table is the same with more legroom in a larger
  structure
• To minimize the complexity I kept the proposed
  SAS design to a single stage of passive
  attenuation

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OMC SAS

• The requirement of guaranteeing easy return of
  the alignment after interventions require a set
  of suitable UHV compatible sensors and actuators
• The sensors will read the changes of position
  after interventions and either suggest changes of
  ballast to regenerate the previous balance, or
  use the actuators to return to the original table
  alignment
• A set of LVDT, nanometer resolution, cm range,
  UHV compatible position sensors are adequate for
  the use.
• Low power, UHV compatible voice coils are
  suitable actuators to deal with tidal and thermal
  position changes

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OMC SAS

• The passive attenuation has been designed on the
  basis of inverted pendula in the horizontal
  direction and GAS springs in the vertical
  direction
• Both devices have been successfully used to
  produce 60 or more dB of passive mechanical
  attenuation

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Shaker shaking tower
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HAM implementation
Existing design optical bench
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HAM implementation

• Horizontal direction, x, y, phi
• the IPs

Intermediate platform
legs
Flex joints
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HAM implementation

• Preliminary test results
• 60 dB achieved without counterweight
• 1/8 payload (8 times better at full payload)

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HAM implementation

• vertical direction, the GAS springs

Optical bench
Intermediate platform
GAS springs
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HAM implementation

• The transition between
• LIGO and Advanced LIGO is obtained by simply
  eliminating a number of spacers

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HAM SAS feature

• The expected passive attenuation performance is
  probably good enough for the OMC
• The sensors and actuators satisfying by the
  positioning, tidal and thermal stability
  requirements are compatible with active
  attenuation
• The performance of HAM-SAS can be complemented
  with one stage of active attenuation at marginal
  cost
• This addition would make the OMC HAM SAS a
  viable, more inexpensive candidate to replace the
  in-vacuum stiff SEI and is fully compatible with
  the SUS system

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HAM SAS design status

• A practically complete tentative HAM SAS design
  is virtually ready for production
• http//www.ligo.caltech.edu/desalvo/HAM-SAS
  and
• http//www.ligo.caltech.edu/desalvo/HAM-SAS.doc
  
• Preliminary bidding indicate a mechanical
  components cost of 130K (including optical
  bench, excluding accelerometers and motors) with
  production time of the order of three months
• Prototyping of parts of the design will be made
  shortly, fully validating the design
• Scaling of the design is possible both for
  smaller sizes, if deemed necessary, or for larger
  sizes (BSC)