Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Inverted Pendulum Control for KAGRA Seismic Attenuation System 1 D2, Institute for Cosmic Ray Research Takanori Sekiguchi

Italy-Japan Workshop (19 April, 2013) Contents 2 Introduction of IP controls IP control model and simulation Current status of IP control experiment Summary *IP = Inverted Pendulum

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Suspension Local Controls 3 Target: Damping of mechanical resonances Drift control at low frequencies Purpose: Reduction of RMS motions for lock acquisition Quick recovery after large excursion (e.g. EQ) Stable operation of the interferometer RMS displacement0.1 μm RMS velocity0.1 μm/sec RMS yaw and pitch angle0.1 μrad Damping time of resonances~ 1 minute Rough idea of the requirement from MIF:

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) IP Local Control 4 Top stage X, Y, Yaw motions are controlled. Drift control of IP & active damping of resonances (below 1 Hz) Sensitivity of sensors

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Starting Point 5 Starting from 1-D suspension model with simplified system Check controllability with combined sensor (LVDT & geophone) ≡ Simple suspension modelPre-isolator Prototype in Kashiwa

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Control Model 6 (Calibration of the sensors are included in “suspension” block) Geophone senses top stage velocity LVDT senses relative displacement between top & ground Geophone for damping (>0.1 Hz), LVDT for drift control (<0.1 Hz) Sensor Noise

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Filter Design 7 Chebychev filter for steep cut-off around micro seismic peak High pass filter to reject glowing- up noise at low frequencies Gain boost at micro seismic peak Open-loop transfer function Crossover frequency: 0.03 Hz Unity gain frequency: 0.8 Hz (phase margin: 60 deg.)

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Frequency Response to Seismic Motion 8 Active Isolation at micro seismic peak No seismic reinjection above 5 Hz Resonance is damped

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Noise Budget in Normal day RMS dis.: 1.5x10 -6  2x10 -6 m Hz) RMS vel.: 1.5x10 -7  2x10 -7 m/s Geophone Noise

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Noise Budget in Stormy day RMS dis.: 2x10 -5  6x10 -6 m Hz) RMS vel.: 2x10 -6  5x10 -7 m/s

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Summary 11 We investigate IP controls with combined vibration sensors (LVDTs and geophones). Sensor noise (especially, geophone) is dominant with quiet environment in Kamioka mine. Low frequency vibration (<10 mHz) should be stabilized by other ways (global control).

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Current Status of Pre-Isolator Prototype in Kashiwa 12 IP is currently tuned at 80 mHz. LVDTs and geophones are installed and calibrated. X, Y, θ motions constructed by LVDTs and geophones resemble very well. Measured Y displacement by LVDT & geophone With excitation from virtual Y actuator Next step: Apply X control with combined sensors

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) END 13

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Appendix 14

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Why Local Controls Are Necessary? 15 Multi-suspension system has many mechanical resonances to be damped. Low frequency oscillators are sensitive to disturbance like temperature change, and drift easily. Local controls are required for lock acquisition and stable operation of the interferometer

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Requirement 16 For Lock Acquisition: Small RMS velocity and rotation angle of the mirror: RMS velocity~0.1 μm/sec RMS yaw and pitch angle~0.1 μrad Rough idea of the requirement: Short damping time of the mechanical resonances (within ~min.) During Operation: Actuation forces on the mirrors must be within the actuator range. (e.g. ~0.1 μm displacement level is allowed for test masses) 10 times smaller local control noises than other fundamental noises in the observation band.

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Control Topology 17 Top Stage LVDT: Drift control Geophone: Damping of pendulum modes Intermediate Mass Damping of residual resonances Alignment control Optical Lever Damping angular resonances? DC alignment signal

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Control Topology 18 X, Y Damp: GEO, OSEM DC: LVDT Z Damp: LVDT, OSEM DC: LVDTs on GAS Pitch, Yaw Damp: OSEM DC: Oplev Roll Damp: OSEM

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Resonances of Pendulum modes 19 Resonances at low frequencies contribute to RMS Damped by magnetic damper, but not perfectly Simulated Mechanical TF of Type-A SAS Pendulum seismic peak

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Pole Plot 20

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Pole Plot [variable gain] 21 Too small gain  unstable by LVDT control (~0.2 Hz) Too much gain  unstable by geophone control (~0.01 Hz) Pole plot with variable gain of geophone control (gain 0 to 5, Blue: gain = 1)

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Noise Budget in Normal day Geophone Noise

Takanori Sekiguchi Italy-Japan Workshop (19 April, 2013) Noise Budget in Stormy day