Resonant Gravitational Wave Detectors

1
Resonant Gravitational Wave Detectors
TAUP 2003 EIGHTH INTERNATIONAL WORKSHOP
ONTOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS

• bars and spheres

2
Gravitational waves
Replace gravitational field by curvature of
spacetime
3
Gravitatonal waves
Einsteins equations have form similar to the
equations of elasticity. PEh (Pstress,
hstrain, EYoungs mod.) T(c4/8pG)G Tstress
tensor, GCurvature tensor and c4/8pG1042N is a
space-time stiffness (energy density/unit
curvature) ?Space-time can carry waves. ?They
will have very small amplitude ?There will be a
large mismatch with ordinary matter so very
little energy will be absorbed (very small
cross-section)
4
Gravitational waves
5
Gravitational waves
6
Gravitational waves
7
Gravitational waves detectors
Resonant cylinder
Laser interferometer
Resonant sphere
laser
8
Cylindrical Detectors
optimal direction and polarization
9
Cylindrical Detectors
10
Cylindrical DetectorsSensitivity of resonant
detectors

• Noise in the detector
• Extrinsic Seismic noise ? mechanical filter
• Intrinsic Thermal noise ? cool detector
• amplifier noise ? SQUID amplifier

amplifier
transducer
11
(No Transcript)
12
Cross section
Cross section for a sphere
For a bar F2?0
(Lobo-Coccia)
13
Sensitivity
Minimum detectable energy TeffT/?Q 2TN
For a SQUID noise energy of one quantum
Need??0.1 Q107 T20 mK
14
The resonanttransducer
The displacement of the secondary
oscillator modulates a dc electric or magnetic
field or the frequency of a s.c. cavity
xM
xm
15
Bandwidth
16
The resonant transducerDifferent types
mushroom
rosetta
17
Resonant Bar EXPLORER
18
EXPLORER 2 ton Al bar 3m long 0.6 m diam.
The noise temperature is lt 3 mK (h4.4 10-19) for
84 of the time. It is taking data, equipped
with a rosette capacitive transducer and a
commercial Quantum Design dcSQUID. The peak
strain sensitivity is 10-21/vHz and the bandwidth
30 Hz _at_ 10-21/vHz Cosmic ray detectors installed
1998
2001
2003
19
Bar DetectorsNautilus
Materialaluminium vs 5400 m/s Length3meter Mas
s2300kg freq900 Hz
20
NAUTILUS 2003

• New bar tuned to na 935 Hz
• new antenna suspension cable
• new capacitive transducer
• Quantum Design dc SQUID

The bar was cooled down to 3.5 K in April. Data
taking is under way. The peak strain sensitivity
is 2 x 10-21/v Hz and the bandwidth 30 Hz
_at_10-20/v Hz
21
1.3 mK
2003
Tbar3.5 K
3 mK
2001
3 mK
Tbar1.5 K
3 mK
22
NAUTILUS spectral density at 3.5 K June 2003
210-21
2001
Expected spectral density at 0.15 K
610-22
1.610-22
23
Resonant DetectorsAuriga
L3 m M2000 kg F900Hz T150 mK
24
AURIGA II run (mid 2003)
25
AURIGA II run (mid 2003) upgrades
new mechanical suspensions attenuation gt 360
dB at 1 kHz FEM modelled new capacitive
transducer and s.c. transformer two-modes (1
mechanical1 electrical) optimized mass new
amplifier double stage SQUID 200 h energy
resolution new data analysis C object
oriented code frame data format
26
Resonant barNIOBE (discontinued operation)
Parametric transducer Nb bar with m1500 kg,
f700 Hz T5.5K h3x10-19
27
Resonant barALLEGRO (Louisiana)
28
Bar DetectorALLEGRO

• Specifications
• Antenna mass m11150 Kg (Al) Q9x106 _at_4.4K
• Second mass m25.35 Kg (Nb) Q3x106
• Third mass m30.050 Kg (Nb) Q3x106 4.8
  cm Ø, gap 50 ?m
• Two-stage QD SQUID with 300? noise at 920 Hz
• Calculated sensitivity
• ?f100 Hz h7.6x10-20 TN 1.3x105 K

29
Bar DetectorALLEGRO Transducer sensitivity
30
Bar DetectorALLEGRO
Transducer built by the Maryland group H.J.Paik,
H.Vol Moody and A.Weber (Proc. Amaldi-5
conference 2003)
31
Resonant SpheresCharacteristics of spherical
detectors

• Much larger cross-section that a bar of the same
• resonant frequency (up to 70 x)
• Omni-directional Allows determination
• of direction and polarization.
• Short cool-down time (28 hours to 4K for
  MiniGrail)
• Cryogenics is cheaper because of smaller dewar.
• Require 6 transducers
• hollow spheres could allow large choice of
• cross-sections and frequencies.
• The low cost (500k) allows making N spheres
• thus gaining in sensitivity with vN

32
Transducer location (TIGA)
www.minigrail.nl
33
Spherical detectorsMiniGrail (Leiden)
Material CuAl6 Density
? 8000 kg/m3 Diameter ? 0.65 m Mass
M 1150 kg Sound velocity v 4000
m/s Resonant freq. f 3160 Hz T-sphere
T78 mK hQL4x10-23/vHz Problems to solve
1-internal heat leak 2-abnormally low Q
(1.5x106) 2-Noise from 1K pot 3-SQUID amplifier
A.De Waard, L.Gottardi et al. Proc. 5th Amaldi
conference 2003
34
Spherical detectorsMario Schenberg.

• All the "heavy" parts (cryogenic chambers,
  antenna vibration isolation system, and the
  antenna itself) are already assembled.
• Antenna was cooled to 2K

35
Spherical detectorMario Schenberg (Brazil)
Three-mode parametric transducer m11150 Kg
m253g m30.01g Expected sensitivity with this
system h 10-21vHz 50Hz bandwidth O.D.de
Aguiar et al, Proc. Amaldi 5, 2003
36
Quality Factor of MiniGrail, Schenberg and small
15Kg CuAl 6 sample.
37
DUAL wideband high freq gw detectorPRL 87
(2001) 031101 gr-qc/0302012
2 nested resonant masses
Sensitive in a kHz-wide frequency band
Mo Dual 16.4 ton height 2.3 m Ø 0.94m
SiC Dual 62.2 ton height 3 m Ø 2.9m
T0.1 K , Standard Quantum Limit
readout selects quadrupolar deformations
averages over a wide area
? flat sensitivity in a wide band
38
EXPLORER-NAUTILUS 2001 data analysis
During 2001 EXPLORER and NAUTILUS were the only
two operating resonant detectors, with the best
ever reached sensitivity. A new algorithm based
on energy compatibility of the event was applied
to reduce the background
Number of events
Sidereal hours
ROG Coll. CQG 19, 5449 (2002) L.S.Finn CQG 20,
L37 (2003) P.Astone, G.DAgostini, S.DAntonio
CQG Proc. Of GWDAW 2002, gr-qc/0304096 E. Coccia
ROG Coll.CQG Proc. Of GWDAW 2002 ROG Coll.
gr-qc/0304004
New data needed with more antennas in coincidence
39
Conclusions

• Resonant detectors are well understood and
• the roadmap for improvements is clear Important
  points are
• 1-Increse ? to increase bandwidth
• 2-Decrese TN by developing low-noise SQUIDs
• 3- Decrease external interferences (shielding,
  vibrations,.. )
• Spherical detectors will soon be operational and
  will help pinpointing the direction of sources,
  (once detected).
• Arrays of spheres could give spectral
  sensitivities in the 10-24 range at frequencies
  above 1 kHz
• Long coincidence measurement periods with 3 or
  more antennas will allow to understand the cause
  of the signals seen by the Roma group (maybe new
  Physics?)
• Dual detectors might make wide-band high
  frequency region accessible at very high
  sensitivities

40
(No Transcript)