Design overview

Main suspension

SF: The top stage with a GAS filter for vertical seismic isolation.
BF: The second stage with a GAS filter for vertical seismic isolation. It is suspended from SF GAS.
BFRM: The recoil mass for the BF. It is suspended from the ground. It has function to sense the relative position between the BF and BFRM and actuate the BF in 6 DOFs using BF LVDTs.
IM: The third stage suspended from the BF GAS.
IRM: The recoil mass for the IM. It is also suspended from the BF. It has function to sense the relative position between the IM and IRM and actuate the IM in 6 DOFs using OSEMs.
Optic: The optic for the interferometer. It is suspended from IM. It has 4 magnets for actuation.
RM: The recoil mass for the optic. It is also suspended from IM. It has function to actuate the optic using the coils with OSEM bodies. We use Optical Lever to sense the optic position.
Traverser: The stage with 4 motors to actuate the whole suspension in horizontal direction.
Earthquake stop (EQ stop): The structure to protect the suspension from the large shocks, or to fix the suspension not to swing too much and be broken during installation phase.

Optical bench is suspended as double stage pendulum. The intermediate stage has the magnetic damper ring that is also suspended from the ground.

The frame just inside the chamber that is fixed on the ground.

We use the Oplev for sensing both tilt and length displacement. See JGW-T1605788.