Date post: | 22-Dec-2015 |
Category: |
Documents |
View: | 216 times |
Download: | 3 times |
LIGO-G020518-00-W
Status of the Laser Interferometer Gravitational-Wave Observatory
Reported on behalf of LIGO colleagues by
Fred Raab,
LIGO Hanford Observatory
Status of LIGO 2LIGO-G020518-00-W
Laser Interferometer Gravitational-wave Observatory
LIGO Mission: To sense the distortions of spacetime, known as gravitational waves, created by cosmic cataclysms and to exploit this new sense for astrophysical studies
Over nearly 400 years, astronomy has developed many clever ways to “see” and study the universe; LIGO hopes to add a “sound track” using interferometers that function like large terrestrial microphones, listening for vibrations of space.
Status of LIGO 3LIGO-G020518-00-W
Gravitational Collapse and Its Outcomes Present LIGO Opportunities
fGW > few Hz accessible from earth
fGW < several kHz interesting for compact objects
Status of LIGO 4LIGO-G020518-00-W
Potential LIGO Sources
Supernovae, with strength depending on asymmetry of collapse
Inspirals and mergers of compact stars, like black holes, neutron stars
Starquakes and wobbles of neutron stars and black holes
Stochastic waves from the early universe, cosmic strings, etc.
Unknown phenomena
Status of LIGO 5LIGO-G020518-00-W
Gravitational Waves
Gravitational waves are ripples in space when it is stirred up by rapid motions of large concentrations of matter or energy
Rendering of space stirred by two orbiting black holes:
Status of LIGO 6LIGO-G020518-00-W
Catching WavesFrom Black Holes
Sketches courtesy of Kip Thorne
Status of LIGO 7LIGO-G020518-00-W
Energy Loss Caused By Gravitational Radiation Confirmed
In 1974, J. Taylor and R. Hulse discovered a pulsar orbiting a companion neutron star. This “binary pulsar” provides some of the best tests of General Relativity. Theory predicts the orbital period of 8 hours should change as energy is carried away by gravitational waves.
Taylor and Hulse were awarded the 1993 Nobel Prize for Physics for this work.
LIGO-G020518-00-W
How does LIGO detect spacetime vibrations?
Status of LIGO 10LIGO-G020518-00-W
Important Signature of Gravitational Waves
Gravitational waves shrink space along one axis perpendicular to the wave direction as they stretch space along another axis perpendicular both to the shrink axis and to the wave direction.
Status of LIGO 11LIGO-G020518-00-W
Laser
Beam Splitter
End Mirror End Mirror
ScreenViewing
Sketch of a Michelson Interferometer
Status of LIGO 12LIGO-G020518-00-W
LIGO (Washington) LIGO (Louisiana)
The Laser InterferometerGravitational-Wave Observatory
Supported by the U.S. National Science Foundation; operated by Caltech and MIT; the research focus for more than 400 LIGO Scientific Collaboration members
worldwide.
Status of LIGO 13LIGO-G020518-00-W
2998 km
(+/- 10 ms)
CIT
MIT
The Four Corners of the LIGO Laboratory
Observatories at Hanford, WA (LHO) & Livingston, LA (LLO)
Support Facilities @ Caltech & MIT campuses
LHO
LLO
Status of LIGO 14LIGO-G020518-00-W
Part of Future International Detector Network
LIGO
Simultaneously detect signal (within msec)
detection confidence locate the sources
decompose the polarization of gravitational waves
GEO VirgoTAMA
AIGO
Status of LIGO 15LIGO-G020518-00-W
Spacetime is Stiff!
=> Wave can carry huge energy with miniscule amplitude!
h ~ (G/c4) (ENS/r)
Status of LIGO 16LIGO-G020518-00-W
Some of the Technical Challenges
Typical Strains less than ~ 10-21 at Earth ~ 1 hair’s width at 4 light years
Understand displacement fluctuations of 4-km arms at the millifermi level (1/1000th of a proton diameter)
Control arm lengths to 10-13 meters RMS Detect optical phase changes of ~ 10-10 radians Engineer structures to mitigate recoil from atomic
vibrations in suspended mirrors Provide clear optical paths within 4-km UHV beam
lines
Status of LIGO 17LIGO-G020518-00-W
Recycling Mirror
Optical
Cavity
4 km or2-1/2
miles
Beam Splitter
Laser
Photodetector
Fabry-Perot-Michelson with Power Recycling
Status of LIGO 18LIGO-G020518-00-W
Vacuum Chambers Provide Quiet Homes for Mirrors
View inside Corner Station
Standing at vertex beam splitter
P < 10-6 Torr in chambers to reduce acoustics & molecular Brownian motion
Status of LIGO 19LIGO-G020518-00-W
Beam Tube Provides Distortion-Free 4-km Pathway for Light
Requires P ~ 10-9 Torr H2 Equivalent Baked out by insulating tube and driving ~2000 amps
from end to end
Status of LIGO 20LIGO-G020518-00-W
What Limits Sensitivityof Interferometers?
• Seismic noise & vibration limit at low frequencies
• Atomic vibrations (Thermal Noise) inside components limit at mid frequencies
• Quantum nature of light (Shot Noise) limits at high frequencies
• Myriad details of the lasers, electronics, etc., can make problems above these levels
Status of LIGO 21LIGO-G020518-00-W
Design for Low Background Spec’d From Prototype Operation
For Example: Noise-Equivalent Displacement of 40-meter Interferometer (ca1994)
Status of LIGO 22LIGO-G020518-00-W
Vibration Isolation Systems
» Reduce in-band seismic motion by 4 - 6 orders of magnitude» Little or no attenuation below 10Hz» Large range actuation for initial alignment and drift compensation» Quiet actuation to correct for Earth tides and microseism at 0.15 Hz during
observation
HAM Chamber BSC Chamber
Status of LIGO 23LIGO-G020518-00-W
Seismic Isolation – Springs and Masses
damped springcross section
Status of LIGO 24LIGO-G020518-00-W
Seismic System Performance
102
100
10-2
10-4
10-6
10-8
10-10
Horizontal
Vertical
10-6
HAM stackin air
BSC stackin vacuum
Status of LIGO 25LIGO-G020518-00-W
Core Optics Suspension and Control
Local sensors/actuators provide damping and control forces
Mirror is balanced on 1/100th inchdiameter wire to 1/100th degree of arc
Optics suspended as simple pendulums
Status of LIGO 26LIGO-G020518-00-W
Suspended Mirror Approximates a Free Mass Above Resonance
Status of LIGO 27LIGO-G020518-00-W
IO
Frequency Stabilization of the Light Employs Three Stages
Pre-stabilized laser delivers light to the long mode cleaner
• Start with high-quality, custom-built Nd:YAG laser
• Improve frequency, amplitude and spatial purity of beam
Actuator inputs provide for further laser stabilization
• Wideband• Tidal
10-WattLaser
PSL Interferometer
15m4 km
Status of LIGO 28LIGO-G020518-00-W
Interferometer Control System •Multiple Input / Multiple Output
•Three tightly coupled cavities
•Ill-conditioned (off-diagonal) plant matrix
•Highly nonlinear response over most of phase space
•Transition to stable, linear regime takes plant through singularity
•Employs adaptive control system that evaluates plant evolution and reconfigures feedback paths and gains during lock acquisition
•But it works!
Status of LIGO 29LIGO-G020518-00-W
Steps to Locking an Interferometer
signal
LaserX Arm
Y Arm
Composite Video
Status of LIGO 30LIGO-G020518-00-W
Watching the Interferometer Lock
signal
X Arm
Y Arm
Laser
Status of LIGO 31LIGO-G020518-00-W
Why is Locking Difficult?
One meter, about 40 inches
Human hair, about 100 microns000,10
Wavelength of light, about 1 micron100
LIGO sensitivity, 10-18 meter000,1
Nuclear diameter, 10-15 meter000,100
Atomic diameter, 10-10 meter000,10
Earthtides, about 100 microns
Microseismic motion, about 1 micron
Precision required to lock, about 10-10 meter
Status of LIGO 32LIGO-G020518-00-W
Tidal Compensation Data
Tidal evaluation on 21-hour locked section of S1 data
Residual signal on voice coils
Predicted tides
Residual signal on laser
Feedforward
Feedback
Status of LIGO 33LIGO-G020518-00-W
Microseism
Trended data (courtesy of Gladstone High School) shows large variability of microseism, on several-day- and annual- cycles
Reduction by feed-forward derived from seismometers
Microseism at 0.12 Hz dominates ground velocity
Status of LIGO 34LIGO-G020518-00-W
Background Forces in GW Band = Thermal Noise ~ kBT/mode
Strategy: Compress energy into narrow resonance outside band of interest require high mechanical Q, low friction
xrms 10-11 mf < 1 Hz
xrms 210-17 mf ~ 350 Hz
xrms 510-16 mf 10 kHz
Status of LIGO 35LIGO-G020518-00-W
Thermal Noise Checked in 1st Violins on H2, L1 During S1
Almost good enough for tracking calibration.
Status of LIGO 36LIGO-G020518-00-W
Chronology of Detector Installation & Commissioning
7/98 Begin detector installation 6/99 Lock first mode cleaner 11/99 Laser spot on first end mirror 12/99 First lock of a 2-km Fabry-Perot arm 4/00 Engineering Run 1 (E1) 10/00 Recombined LHO-2km interferometer in E2 run 10/00 First lock of LHO-2km power-recycled interferometer 2/01 Nisqually earthquake damages LHO interferometers 4/01 Recombined 4-km interferometer at LLO 5/01 Earthquake repairs completed at LHO 6/01 Last LIGO-1 mirror installed 12/01 Power recycling achieved for LLO-4km 1/02 E7: First triple coincidence run; first on-site data analysis 1/02 Power recycling achieved for LHO-4km 9/02 First Science Run (S1) completed 2/03 Second Science Run (S2) begun
Status of LIGO 37LIGO-G020518-00-W
LIGO SensitivityLivingston 4km Interferometer
May 01
Jan 03
Status of LIGO 38LIGO-G020518-00-W
S1 Analysis Working Groups
Data from S1 is being analyzed by LSC working groups for:» Detector Characterization – monitors of data quality, instrument
diagnostics, tuning displays
» Binary Inspirals – modeled chirps from BH’s, NS’s, MACHO’s
» Bursts – unmodeled deviations from stationarity; independent searches; searches triggered on GRB’s, SN’s
» Periodic Sources – known pulsar search; work toward all-sky search for unknown pulsars
» Stochastic Background – early universe
Status of LIGO 39LIGO-G020518-00-W
Summary
First triple coincidence run completed (17 days with ~23% triple coincidence duty factor)
On-line data analysis systems (Beowulf parallel supercomputer) functional at LHO and LLO
S1 coincidence analyses with GEO & TAMA are first science analyses with international laser-GW network
First science data analysis ongoing Interferometer control system still being commissioned and
tuned Working to increase immunity to high seismic noise periods
(especially important at LLO) S2 running 14Feb03 – 14Apr03
Status of LIGO 40LIGO-G020518-00-W
Future Plans
Improve reach of initial LIGO to run 1 yr at design sensitivity
Advanced LIGO technology under development with intent to install by 2008
Planning underway for space-based detector, LISA, to open up a lower frequency band ~ 2015
Status of LIGO 41LIGO-G020518-00-W
Despite a few difficulties, science runs started in 2002.