Control strategy in the vibrtion iControl strategy in the vibrtion isolation system for KAGRAsolation system for KAGRA

Ryutaro TakahashiRyutaro Takahashi(Institute for Cosmic Ray Research, Univ. of Tokyo(Institute for Cosmic Ray Research, Univ. of Tokyo

/ / National Astronomical Observatory of Japan)National Astronomical Observatory of Japan)

The 3rd Korea-Japan workshop on KAGRASogang University, Seoul 21-22 December, 2012

ContentsContents1.1. VVibration isolation systemibration isolation system for KAGRA for KAGRA2.2. Control systemControl system3.3. Low frequency disturbanceLow frequency disturbance

1.1. Seismic noiseSeismic noise2.2. Ground strainGround strain3.3. Thermal driftThermal drift4.4. Newtonian noiseNewtonian noise

4.4. Control strategyControl strategy1.1. Hierarchical contolHierarchical contol2.2. Common mode rejectionCommon mode rejection3.3. Feed-forward controlFeed-forward control

5.5. ConsiderationConsideration6.6. SummarySummary

11.. V Vibration isolation systemibration isolation systemfor KAGRAfor KAGRA

Top filter[Filter0]

Inverted Pendulum (IP)

Bottom Filter (BF)

Test Mass (TM)Recoil Mass (RM)

Pre-isolator

Payload

Filter chain

Schematic Schematic view of Seiview of Seismic attenusmic attenuation systeation syste

mm(SAS)(SAS)

Type-A/BType-A/B

Intermediate Mass (IM)Intermediate Recoil Mass (IRM)

Geometric Anti-Spring (GAS)Filter1 (Filter1~3 in Type-A)

Type-AIP + GAS Filters (5 stages)

+ Payload (23kg, cryogenic)

Type-BIP + GAS Filters (3 stages)

+ Payload (10kg/20kg)Type-C

Stack + Single/Double-pendulum (~1kg)

Disposition of vibration isolation systemDisposition of vibration isolation system

Type-A (2-layer structure) Type-A (2-layer structure)

Upper tunnel containing Upper tunnel containing pre-isolator (short IP pre-isolator (short IP and and ttop filter)op filter)

1.2m diameter 5m tall 1.2m diameter 5m tall borehole containing borehole containing standard filter chainstandard filter chain

Lower tunnel containing Lower tunnel containing cryostat and payloadcryostat and payload

8m

5m

7m

1F

2F

Type-BType-B

IP base is supported IP base is supported by the outer frame.by the outer frame.

Pre-isolator is the Pre-isolator is the same as Type-A’s.same as Type-A’s.

Type-B Payload

Rigid table

Type-C Payload

Stack

Type-CType-CType-B payload Type-B payload

on on rigid tablerigid table

22.. Contol Contol system system

Pre-isolatorPre-isolator

Type-B PayloadType-B Payload

Linear variable differencial transformer (LVDT) and Voice coil actuator

Embeded LVDT-actuator unit on the inverted pendlum.

Evaluation of LVDT. The noise level was less then 0.1m at 0.01-0.1Hz. The noise level is proportional to DC offsets.

Prim

aly

co

il

Se

con

da

ly c

oil

Yo

ke

Co

il

Magnet

VC

LVDT

Evaluation of L4-C geophones in Kamioka. The noise level was 5x10-11 m Hz1/2 at 1Hz. Test of geophones and preamplifirs

in Kashiwa.

Vertical

Velocity responce of L4-C geophone.

Ground 1

Ground 2

Differential

Inertial sensor(Geophone)

Motor slider and Hydraulic leveler

Level of the IP base is tuned by the tripodal hydraulic piston.

Position of the IP is tuned by the motor sliders to compensate the DC component of the feedback signal to the actuator.

The sensitivity is ~ 2.5x10-10 m/Hz1/2 at 1 Hz, and ~7x10-10 m/Hz1/2 at 0.1 Hz.

The linear range is ~ 1mm.

Optical sensor and electro-magnetic actuator(OSEM)

Optical lever

by K. Agatsuma

Type-B

Control of IPControl of IP(example of (example of

TAMA)TAMA)PS

Length

ACC, LVDT

X

ACC

LVDT

Actuator

X

Y

Global control of cavity Length after cavity lock

Damping of excited torsion mode using Position Sensor

33.. Low frequency disturbance Low frequency disturbance

Peterson noise model

Acceleration spectrumDashed lines: Peterson high and low noise modelsSolid lines: noise spectral level for IRIS station (3 components)

Global high (NHNM) and low (NLNM) noise models represent upper and lower bounds of a cumulative compilation of representative ground acceleration power spectral densities.

3-1. Seismic noise

J. Havskov and G. Alguacil, “Instrumentation in Earthquake Seismology”, Springer, 2009

Origin of seismic noiseMan made noise (Cultural noise)•Originates from traffic and machinery with high frequencies (>2-4Hz).•Propagates mainly as high-frequency surface waves which attenuate fast with distance and decrease strongly in amplitude with depth.•Has a large difference between day and night.

Wind noise•Makes any object move.•Usually high frequency, however large swinging objects can generate lower frequency signals.

Horizontal noise attenuation (dB, spectral acceleration density) as a function of depth and period

Ocean generated noise (microseisms, microseismic noise)•Seen globally.•Long period (10~16s): generated only in shallow waters in coastal region.•Shorter period (peak~5s): generated by the superposition of ocean waves of equal period traveling in opposite directions.

3-1. Seismic noise

3-2. Ground strain

JGW-G1000063 by A. Araya

Tidal variation

3-3. Thermal drift

R. Takahashi, et al : Rev. Sci. Instrum. 73 (2002) 2428

Stack isolation in Type-C system

NaNaiive estimationve estimation

Generally this noise is Generally this noise is smaller in underground.smaller in underground.Large amount of moving Large amount of moving water due to melted snow water due to melted snow may make effective noise may make effective noise in spring around Kamioka.in spring around Kamioka.

3-4. 3-4. Newtonian noiseNewtonian noise

Ambient seismic waves induce density perturbations, which produce fluctuating gravitational forces.

Estimated Newtonian noise in LIGO (Hughes and Thorne, PRD 58 122002)

44.. Control strategy Control strategy

4-1. Hierarchical control4-1. Hierarchical control

Actuation Sensing Control Band

Moter Slider on IP

Offset of VC

1/day

Voice Coil on IP

LVDT <0.1Hz

Geophone 0.1-1Hz

Global <0.1Hz

Intermediate Mass

OSEM <1Hz

Global 0.1-1Hz

Test Mass Global 1-1kHz

Actuation Sensing Control Band

Moter Slider on Filter0

Offset of VC

1/day

Voice Coil on Filter0

LVDT <1Hz

Voice Coilon Filter1-3

LVDT 0.1-1Hz

Intermediate Mass

OSEM <1Hz

Displacement

horizontal vertical

4-1. Hierarchical control4-1. Hierarchical control

Actuation Sensing Control Band

Hydraulic leveler on IP

Offset of VC

1/day

Moter Slider on IM

Offser of TM

1/day

Intermediate Mass

OSEM <1Hz

Test Mass Optical Lever

<1Hz

Global <0.1Hz

Actuation Sensing Control Band

Moter Slider on Filter0

Offset of TM

1/day

Voice Coil on IP

LVDT <0.1Hz

Geophone 0.1-1Hz

Intermediate Mass

OSEM <1Hz

Test Mass Optical Lever

<1Hz

Global <0.1Hz

Angle

pitch yaw

4-2. Common mode rejection (CMR)4-2. Common mode rejection (CMR)

The interferometer senses The interferometer senses not local displacement but lenot local displacement but length between mirrors.ngth between mirrors.The mirrors move in commThe mirrors move in common mode at low frequencies.on mode at low frequencies.Microseismic noise was redMicroseismic noise was reduced by the common mode ruced by the common mode rejection in TAMA or CLIO.ejection in TAMA or CLIO.Such a reduction is not expSuch a reduction is not expected in the 3-km cavity of Kected in the 3-km cavity of KAGRA.AGRA.

Witness sensor is effected by Witness sensor is effected by the the feed-back feed-back control.control.Witness sensor is NOT effected by Witness sensor is NOT effected by the the feed-forwardfeed-forward control. control.

4-3. 4-3. Feed-forward controlFeed-forward control

WitnessSensor

FilterWitnessSensor

Filter

Targetsignal

Targetsignal

WitnessSensor

Filter

Targetsignal

feed-backfeed-back feed-forwardfeed-forward

feed-forward (offline)feed-forward (offline)

Comparision with feed-back control

55. . ConsiderationConsideration There are many kinds of servo loops. Control bands arThere are many kinds of servo loops. Control bands ar

e limited by the sensing noises.e limited by the sensing noises.

A large disturbance at low frequencies should be fedbaA large disturbance at low frequencies should be fedback to the upper reaches considering phase delay.ck to the upper reaches considering phase delay.

Sensing signals must be diagonalized well for independSensing signals must be diagonalized well for independent controls.ent controls.

CMR at the low frequencies is not effective in the lengtCMR at the low frequencies is not effective in the length control of the 3-km cavity, it is expected only in the ceh control of the 3-km cavity, it is expected only in the center area.nter area.

Feed-forward control is useful in the cace of having indFeed-forward control is useful in the cace of having independent monitor like seismometer (seismic noise), strependent monitor like seismometer (seismic noise), strain meter (tidal variation), or gravity gradiometer (Newtain meter (tidal variation), or gravity gradiometer (Newtonian noise).onian noise).

66. Summary. Summary KAGRA employed the SAS which consists of an KAGRA employed the SAS which consists of an

inverted pendulum and geometric anti-spring filters.inverted pendulum and geometric anti-spring filters.

There are some kinds of displacement noise sources at There are some kinds of displacement noise sources at frequencies lower than 1Hz as well as observation banfrequencies lower than 1Hz as well as observation bandd..

The The vibration isolation systemvibration isolation system is controled by multiple sis controled by multiple servo loops using many kinds of sensors and actuatorservo loops using many kinds of sensors and actuators..

Hierarchical control is required considering sensing noiHierarchical control is required considering sensing noises, CMR and feed-forward loopsses, CMR and feed-forward loops..