The Virgo detector: status and first experimental results. Nicolas Arnaud CERN EP Seminar 17/03/2003. Outline. The quest for gravitational waves ( GW ): a long history Detection principles Interferometric detectors Description of the Virgo interferometer Optical scheme
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Nicolas Arnaud CERN EP Seminar 17/03/2003
«J'ai été d'abord conduit à supposer que la propagation de
la gravitation n'est pas instantanée mais se fait à la vitesse
de la lumière (…) Quand nous parlerons donc de la position ou
de la vitesse du corps attirant, il s'agira de cette position ou
de cette vitesse à l'instant où l'onde gravifique est partie de
ce corps (…)» [Italics of the author]
«GW travel at the speed of mind » Sir A.S. Eddington
GW must exist !
L + DL
Ex:Jupiter radiates 5.3 kW as GW during its orbital motion
Luminosity G/c5 10-53 W-1
No Hertz experiment possible!
GW effect : differential modification of lengths
Detectors:IFO, resonant bars, LISA…
Detections expected up to the Virgo cluster (~ 20 Mpc)
Mirrors used as
Variation of the
power Pdet at the
IFO output port
Site: Cascina, near Pisa
Laser power: Pin = 20 W
Sensitivity : hsens ~
To increase the arm length : 1 m 3 km
To add Fabry-Perot cavities (Finesse = 50 Gain = 30)
To add a recycling mirror (P = 1 kW on the Beam Splitter)
Length ~ 7 m; Mass ~ 1 ton
Structure in inverted pendulum
fres ~ 30 mHz
~ 1014 à 10 Hz
Tail of the
0.6 Hz marionetta/
Minimum ~3 10-23between ~ 500 Hz et 1 kHz
~ 6 m
The CITF is not sensitive enough:
no hope to collect data with GW signal!!!
Very narrow Working Point
In addition: residual low frequency motion of mirrors (0.6 Hz)
CITF active controls needed (local and global)
dl ~ 10-10 – 10-11 m
dq ~10-9 – 10-7 rad
Control aim: to go from an initial
situation with random mirror
motions to the Virgo working point
~ 0.5 mm
June 13th 2001
December 16th 2001
Correction applied on the Recycling Mirror
All sources of control losses understood
Improvements already done or in progress
June 2001 July 2002
@ 10 Hz
@ 1 kHz
Readout electronic noise
Back scattered light
on laser bench
peaks = qx
due to vibrations
of the input
noise + some
lowered, other sources previously hidden appear!
« As a first conclusion, the tube is straight! »
Thursday March 13th 2003:
First beam travelling in the 3km North Arm!!!
amplitude and frequency
increase with time until
the final coalescence
to go beyond this limit!
Waveform analytically estimated by developments in v/c
Wiener (optimal) filtering used for data analysis
compare candidates selected in 2 different time periods
The detectable GW amplitude is a linear combinationof the
two GW polarizations h+ et h
h(t) = F+ h+(t) + F h(t)
RMS ~ 0.45
Right ascension a
Reduction of a factor ~ 2
in average of the amplitude
not prove yet there can fulfill their requirements
The future of gravitational astronomy looks bright.
That the quest ultimately will succeed seems almost assured.
The only question is when, and with how much further effort.
[I]nterferometers should detect the first
waves in 2001 or several years thereafter (…)
Km-scale laser interferometers are now coming on-line, and it
seems very likely that they will detect mergers of compact
binaries within the next 7 years, and possibly much sooner.
Kip S. Thorne