Masaki Ando, Akiteru Takamori, Kimio Tsubono Department of Physics, University of Tokyo Earthquake...
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Transcript of Masaki Ando, Akiteru Takamori, Kimio Tsubono Department of Physics, University of Tokyo Earthquake...
Masaki Ando, Akiteru Takamori, Kimio TsubonoDepartment of Physics, University of TokyoEarthquake Research Institute, University of Tokyo
1st International LISA-DECIGO workshop (Nov. 12-13, 2008 )
Development of a Low-Frequency Gravitational-Wave Detector Using Magnetically-Levitated Torsion Antenna
Collaborator
Koji ISHIDOSHIRO (University of Tokyo)
Outline
Ground-based low-frequency GW detector realized by Magnetically-Levitated Torsion Antenna
Background and purpose Detection principle key technology (Magnetic Levitation) Prototype experiments Summary
Table of Content
Prototype testsStudy basic ideas and fundamental noises
Background and purpose
Low-frequency GWsLarge amplitude, Interesting sources
Supermassive Black Holes and Inflation of the Universe
GW detectorsGround-based Interferometers
Test mass suspended to be free mass
No sensitive to GWs under resonant frequencyof suspension (~1Hz)
Space InterferometersAlmost free mass
Not easy
Background
Purpose Early implement a ground-based low-frequency GWs detector Detect GWs, or set upper limits
Detection principleTorsion antenna
Bar-shaped test massTidal force of GWs induce rotation of test mass
GW signals are detected from rotation measurement
Tidal force of x-polarized GWs
Rotation
x
y
z
Equation of motion
: shape factor typical ~ 1
Free rotation without loss
Torsion antenna have fundamentally sensitive to low-freq. GWs
Key Technology
Magnetic-LevitationPinning effect between a Permanent magnet (PM) and a superconductor magnet (SCM)
Test mass
PM
SCM
Difficulty to get free rotation without loss
Restoring force with loss in its rotational degree freedom
In principle Stable levitation Free rotation without loss in it rotational degree freedom
Fiber suspension
Prototype experiment
Superconductor magnet Gd-Ba-Cu-O φ60mm,t20mm Critical temp. 92KCryo-Cooler Pulse-tube (low-vibration) Lowest Temp. 62KVacuum Maintained at ~10-3 Pa by turbo pomp
Experimental setup
PurposeStudy basic ideas and fundamental noises Practical loss and spring constant Rotational stability
Superconductormagnet
36cm
120cm
Optical table
Mirrorfor interferometer
Torsion Antenna
Permanentmagnet
Pulse-tubeCryo-cooler
Valveunit
From Ando’s talk at amaldi7
30cmTest mass
Superconductormagnet
Cryo-Cooler
Measured loss factor and spring constant
Loss factor:Rotate the levitated PM + columnar test massMonitor the rotational speed by a reflective photo sensor
⇒Exponentially decay -> Loss factor
Spring constant:Stop the levitated PM + columnar test massMonitor the resonance rotational
Resonance frequency -> Spring Constant
PM
Columnar test mass
Mark for measurement
Top view
Bottom view
Results
Methods
Time [sec]
Rota
tion
sp
eed
MeasurementFitting
Thermal noise limitsThermal noise limits
Loss factor
Fundamental torque noise
Measured rotation noises
PD
BS
Laser
AOM
EOMFI
Torsionantenna
MeasurementMichelson interferometer is used for rotational sensorRotational noises are calibrated from feedback signals
Measured rotation noises
Aluminium Mass : 145 gMomentum:1.3x10-3 kg m2
Permanent magnetsfor actuatorNd φ1mm,t5mm
Mirrorsfor interferometer
Permanent magnetNd Φ22mm, t10mm
Torsion antenna
39cm
30cm
Measured rotation noiseResults
3x10-8[rad/Hz1/2] @200mHz
h~3x10-8[1/Hz1/2] @200mHz
For optimal polarized GWs
Noise analysis
Comparison with coupled noises from Seismic motion
Coupling model 2-d simple rigid-body pendulum
Misalignment (1mm) suspension center and gravity center
Coupled noises are not negligible
More precision analysis is required
Worst case
Summary
Ground-based low-frequency GW detector
Key technology : Magnetic-levitation (pinning effect)
Prototype antenna
γ=2x10-10[m2kg/s], κ=7x10-8[Nm/rad]
3x10-8[rad/Hz1/2]@200mHz
Study basic ideas and fundamental noises Loss and spring constant
Stability of magnetic levitation
Thermal noise limits 1.3x10-12[1/Hz1/2] @200mHz
may be limited by coupled noises from seismic motion
More precision noise analysis is progressing
Free rotation without loss Stable levitation