Performance Measurement of the Prototype Pre-isolator for KAGRA-SAS

Performance Measurement of the

Prototype Pre-isolator for KAGRA-SASICRR 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

JGW-G1200930

Role of Pre-Isolator

2012/3/24 The 67th Annual Meeting of JPS 2

Top part of KAGRA-SAS

Pre-Isolator

1. Vibration Isolation at a low frequency (< 0.1 Hz) * Attenuate the mirror oscillation at the micro-seismic peak (0.2~0.3 Hz)

2. Control the position and orientation of the system

Role of Pre-isolator

Schematic View of Pre-Isolator


GAS Filter・ Vertical attenuation

Inverted Pendulum・ Horizontal attenuation

Position Sensor (LVDT)Coil-magnet actuator

~1.2 m

Accelerometer

Pre-Isolator Prototype


GAS Filter

Inverted Pendulum

@Kashiwa, ICRR

About this Presentation


Performance measurement of GAS Filter, vertical LVDT, coil-magnet actuator

Geometric Anti-Spring (GAS) Filter


Radially arranged cantilever springs

The horizontal force works as an anti-spring and reduces the resonant frequency of the filter

In principle the frequency can be reduced to zero.

Restoring force

Anti-springforce

Compression

Resonant Frequency Measurement


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

Load~320 kg

Photo sensor

Scale

Resonant Frequency Measurement


Load Increases

LVDT (Linear Variable Differential Transducer)


Non-touching displacement sensor

10 kHz modulation

The voltage induced at the two receiver coils depends on the position of the primary coil.

LVDT Calibration


Micrometer

Res

idua

l [m

V]

LVDT Noise Spectrum


~100 nm/rtHz @ 1 - 50 Hz

As sensitive as TAMA-LVDT

Limited by the noise from the electric circuit (driver)

Force Transfer Function


LVDT

Coil-Magnet Actuator

∝f-2

Random input signal to the actuator

Transfer function from the actuation force to the LVDT signal

With the digital system

Non-Linear Response


Actuator Input Signal

LVDT Output

When the actuator is driven by a high frequency signal (> 2 Hz), the LVDT shows a non-linear response.

The same phenomenon is observed even when the magnet for the actuator is eliminated.

Magnetic field couplings??

Summary, Future Works


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

END2012/3/24 The 67th Annual Meeting of

JPS 15

APPENDIX2012/3/24 The 67th Annual Meeting of

JPS 16

Q-factor Measurement


Chunk 1Chunk 2

Chunk 3

Chunk 4

Divide a ring-down signal to many chunks. The signal in each chunk is fit by the following function

)2sin()/exp( 0 fttAy

Investigating amplitude (A) dependence of the Q-factor (Q=π*f*τ)

Q-factor Measurement


Q-factor increases when the amplitude decreases

Explained by the dissipation controlled by Self-Organized Criticality (SOC)

Displacement Sensor


Linear encoder Mercury 2000 (Micro E systems) Resolution: 80 nm

Photosensor

Scale

Force Transfer Function


Performance Measurement of the Prototype Pre-isolator for KAGRA-SAS

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