LCGT seismic Attenuation System

DRADF DRAFT DRAFT

DRAFT

The LCGT-SAS Seismic Attenuation System

• is a modern, simplified and improved version of the

• Virgo Superattenuators

Two tunnel solution

• LCGT SAS is mounted between two tunnels due to the restrictions from the reserved space for the cryostat

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

Two tunnel solution

• The two tunnel solution requires less rock removal, it is marginally cheaper and much more stable (mining-wise, seismically, and mechanically)

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

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

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.

• Add damping simulation

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

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.

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

F. Frasconi - INFN Pisa 13February 27, 2009

Passive attenuation measurements/CITF

Thermal Noise

Measured Upper Limit

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

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

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)

Payload strategy

• Virgo Design • Uncontrolled test masses– Controlled at lock acquisition

• Magnetic actuators• Need to avoid Eddy current

perturbations on controls• Dielectric masses

Payload strawman

design

• Simple brick-like intermediate mass

• Simple box like intermediate reaction mass

• Virgo style Recoil mass surrounding test mass

100kg

100kg

100kg

• Fused silica or Pyrex structures

• Fused Silica parts bonded with glass frit or UV epoxy

• Possibly Initial LCGT in metal

Test mass evolutionin case of delay of cryogenics

Test mass 10 kg 40 kg80 kg

Recoil mass 80 kg 60 kg20 kg

Auxiliary optics

• LCGT designed with recycler telescopes in mind

• Dedicated low attenuation towers for individual mirrors

Auxiliary opticsexternal structure

• Inverted pendulum table on space frame surrounding vacuum chamber

Auxiliary optics payload

• 10 kg mirrors from LIGO

• Coaxial recoil mass in tandem because– No side occupancy for

folded beams– Transmitted beam clearance