JGW-G1200930
ICRR M2 Takanori Sekiguchi
ICRR, NAOJA, ERIB, Sannio Univ.C, INFN RomaD, NIKHEFE, AEIF
Ryutaro Takahashi, Kazuhiro Yamamoto, Takashi Uchiyama,
Hideharu IshizakiA, Akiteru TakamoriB, Riccardo DeSalvoC, Ettore
MajoranaD, Eric HennesE, Jo van den BrandE, Alessandro BertoliniE,F,
Masatake Ohashi, Kazuaki Kuroda, LCGT Collaboration
Pre-Isolator

Top part of KAGRA-SAS

Role of Pre-isolator
1. Vibration Isolation at a low
frequency (< 0.1 Hz)
* Attenuate the mirror oscillation at the microseismic peak (0.2~0.3 Hz)
2. Control the position and
orientation of the system
2012/3/24
The 67th Annual Meeting of JPS
2
~1.2 m
GAS Filter
・Vertical attenuation
Inverted Pendulum
・Horizontal attenuation
Position Sensor (LVDT)
Coil-magnet actuator
Accelerometer
2012/3/24
The 67th Annual Meeting of JPS
3
GAS Filter
Inverted
Pendulum
2012/3/24
The 67th Annual Meeting of JPS
4

Performance measurement of GAS Filter,
vertical LVDT, coil-magnet actuator
2012/3/24
The 67th Annual Meeting of JPS
5

Radially arranged cantilever springs

The horizontal force works as an antispring and reduces the resonant
frequency of the filter

In principle the frequency can be
reduced to zero.
Restoring force
Compression
Anti-spring
force
2012/3/24
The 67th Annual Meeting of JPS
6


The resonant frequency of the filter is
measured, tuning the load weight and the
blade compression.
Using Mercury 2000 (MicroE systems) as a
displacement sensor
Photo sensor
Load
~320 kg
Scale
2012/3/24
The 67th Annual Meeting of JPS
7
Load Increases
2012/3/24
The 67th Annual Meeting of JPS
8

Non-touching displacement sensor

10 kHz modulation

The voltage induced at the two receiver
coils depends on the position of the
primary coil.
2012/3/24
The 67th Annual Meeting of JPS
9
Residual [mV]
Micrometer
2012/3/24
The 67th Annual Meeting of JPS
10
~100 nm/rtHz @ 1 - 50 Hz
2012/3/24

As sensitive as TAMALVDT

Limited by the noise
from the electric circuit
(driver)
The 67th Annual Meeting of JPS
11
LVDT
Coil-Magnet Actuator

Random input signal to
the actuator

Transfer function from
the actuation force to
the LVDT signal

With the digital system
2012/3/24
∝f-2
The 67th Annual Meeting of JPS
12



When the actuator is driven
by a high frequency signal (>
2 Hz), the LVDT shows a
non-linear response.
Actuator Input Signal
The same phenomenon is
observed even when the
magnet for the actuator is
eliminated.
LVDT Output
Magnetic field couplings??
2012/3/24
The 67th Annual Meeting of JPS
13







Performance measurement on the GAS filter, LVDT and actuator of
the pre-isolator prototype
The top filter can be tuned at ~ 0.2 Hz, and maybe even lower.
The linear signal is observed in LVDT over a range of ~1 cm.
Non-linear couplings between the actuator and LVDT.
Tuning the top filter at lower than 0.1 Hz, and the Q-factor,
hysteresis, stability are checked.
Investigating the cause of the actuator-LVDT couplings
Control test with the inverted pendulums
2012/3/24
The 67th Annual Meeting of JPS
14
2012/3/24
The 67th Annual Meeting of JPS
15
2012/3/24
The 67th Annual Meeting of JPS
16

Divide a ring-down signal to
many chunks. The signal in
each chunk is fit by the
following function
Chunk 1
Chunk 2
Chunk 3
Chunk 4
y  A exp(t /  ) sin( 2ft   0 )

Investigating amplitude (A)
dependence of the Q-factor
(Q=π*f*τ)
2012/3/24
The 67th Annual Meeting of JPS
17

Q-factor increases
when the amplitude
decreases

Explained by the
dissipation controlled by
Self-Organized Criticality
(SOC)
2012/3/24
The 67th Annual Meeting of JPS
18


Linear encoder Mercury 2000 (Micro E systems)
Resolution: 80 nm
Photosensor
Scale
2012/3/24
The 67th Annual Meeting of JPS
19
2012/3/24
The 67th Annual Meeting of JPS
20