LCGT seismic Attenuation System
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Transcript of LCGT seismic Attenuation System
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LCGT seismic Attenuation System
DRADF DRAFT DRAFT
DRAFT
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The LCGT-SAS Seismic Attenuation System
• is a modern, simplified and improved version of the
• Virgo Superattenuators
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Two tunnel solution
• LCGT SAS is mounted between two tunnels due to the restrictions from the reserved space for the cryostat
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Alternatives• The alternatives:– A space frame around the
cryostat • Would have hampered the
installation of the cryostat• Would have been a weaker
support– Hooking the IP support point
from the ceiling of a larger cave• Would have been difficult
dangerous and weaker
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Two tunnel solution
• The two tunnel solution requires less rock removal, it is marginally cheaper and much more stable (mining-wise, seismically, and mechanically)
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LCGT SAS wire length• The 2.2 m wire length between
attenuation filters is determined by the mining requirements : – Minimum 5 m between tunnels– Space needed between the
curved cave ceiling and crane straight beam
• It is not determined by the attenuation requirements of LCGT
5m m
in
2.2 m
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LCGT SAS• It is a prototype for third
generation GWIDs
• Mitigates the technical problems and costs associated with digging large caverns
5m m
in
2.2 m
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LCGT SAS damping strategy• Mode damping is vital for easy
locking of the interferometer• One extra filter is added at the
beginning of the chain to provide passive
Eddy current damping for the attenuation
chain internal modes.
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• Add damping simulation
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LCGT SAS damping strategy• Like in TAMA or Virgo
accelerometers are foreseen for the inverted pendulum table for active attenuation
• In LCGT only a backup
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LCGT SAS pre-attenuation strategy• LCGT SAS has an Inverted
pendulum-top filter • pre-attenuator stage,
to deal with:– Microseismic noise– Tidal movements
• Performs the same functions of the LIGO three active stages.
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Attenuation strategy• Topologically LCGT-SAS is a
Virgo-clone with two less filters than Virgo
• OK because better seismic weather underground
• LCGT SAS is expected to have same or better attenuation capabilities than Virgo
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F. Frasconi - INFN Pisa 13February 27, 2009
Passive attenuation measurements/CITF
Thermal Noise
Measured Upper Limit
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LCGT SAS attenuation strategy• Because of the longer
wires the attenuation should start at 41% lower frequency than Virgo
• LCGT SAS has one more attenuation stage than Advanced LIGO
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Payload strategy
• The payload is defined to be 300 kg• For Cryogenic payload development
see separate presentation• Three options for warm payload:• Initial: 10 kg test masses• Advanced: 40 kg test masses• Heavy: 80 kg test masses
100kg
100kg
100kg
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Payload strategy
• Bottom filter supporting:– Intermediate mass (1 wire on GAS)– Intermediate recoil mass (4 wires)
• Intermediate mass supporting:– Test mass (4
fibers)– Coaxial recoil mass(4 wires)
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Payload strategy
• Virgo Design • Uncontrolled test masses– Controlled at lock acquisition
• Magnetic actuators• Need to avoid Eddy current
perturbations on controls• Dielectric masses
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Payload strawman
design
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• Simple brick-like intermediate mass
• Simple box like intermediate reaction mass
• Virgo style Recoil mass surrounding test mass
100kg
100kg
100kg
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• Fused silica or Pyrex structures
• Fused Silica parts bonded with glass frit or UV epoxy
• Possibly Initial LCGT in metal
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Test mass evolutionin case of delay of cryogenics
Test mass 10 kg 40 kg80 kg
Recoil mass 80 kg 60 kg20 kg
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Auxiliary optics
• LCGT designed with recycler telescopes in mind
• Dedicated low attenuation towers for individual mirrors
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Auxiliary opticsexternal structure
• Inverted pendulum table on space frame surrounding vacuum chamber
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Auxiliary optics payload
• 10 kg mirrors from LIGO
• Coaxial recoil mass in tandem because– No side occupancy for
folded beams– Transmitted beam clearance