Design and performance of the Dual detector with large area capacitive readout 4 rd ILIAS-GW Meeting, October 8 th – 9 th 2007, Tuebingen Paolo Falferi for Dual collaboration - IFN - Trento
Dec 14, 2015
Design and performance of the Dual detector with large area capacitive
readout
4rd ILIAS-GW Meeting, October 8th – 9th 2007, Tuebingen
Paolo Falferi for Dual collaboration - IFN - Trento
Goal of the Dual R&D study
to develop a wideband acoustic detector complementary to the advanced interferometric detectors in the high frequency range (>1 kHz), compact, reliable, (relatively) cheap
to detect signals from• Neutron Star binaries merger• Stellar size Black Hole binaries merger• Newborn Magnetars• Neutron Star bar instabilities
Design Evolution
Original main principles of the Dual detector
•avoid small masses
•measure the displacement between two large masses
•select the quadrupolar modes
dual sphere dual cylinder single-mass dual
MolybdenumRext = 0.5mRint = 0.15mL = 3mM = 22 tonT/Q = 10-8 ε0 Kε0=kbTn/h
Sensitivity of a Single-mass Dual Detector
Optimal Transducer Characteristics0=1Sxx= 6x10-46 m2/HzSff= 1.8x10-23 N2/HzNoise stiffness(Sff/Sxx)1/2 = 1.7x1011 N/m
Quadrupolar FilterX = d1-d2
Noise Matching
Noise matching if K ≈ (SFF/SXX)1/2 = Kn
K mechanical stiffness
Kn readout noise stiffness
Test mass Readout
The optimal noise stiffness for the
single-mass Dual is too high
we have to "soften" the test mass
mechanical amplification
Meq1 meq2 meq3keq1 keq2 keq3
x3x2x1
Measured Displacement
If
Displacement Gain around Resonance
Bandwidth Upper Limit
121 eqeq Mmν≈
31 eqeq mM
23 xx −
321 ννν ==
No Resonant Amplification
0 2000 4000 6000 800010-24
10-23
10-22
10-21
10-20
10-19
Single-mass DUAL k = 1.7x1011 (N/m) Single-mass DUAL with lumped mech. amplifier k = 5x108 (N/m)
Shh1/2
(Hz-1/2
)
Frequency (Hz)
The amplifier that permits the requested gain and bandwidth is "too soft": the readout back action noise spoils the detector performance
No Leverage Amplification(back action noise problem)
Hybrid approach: whips on the external surface
x y
L1L2
Whip (transverse wave concentrator)
3/ 4
1
2Min
y L
x L
⎛ ⎞∝ ⎜ ⎟
⎝ ⎠
Minimum Gain (out of resonance)
Resonant and leverage amplification
Displacement readout atthe end of the whips
MolybdenumRext = 50 cmL = 3 mWhip length=32 cmReadout: SQLT/Q: 5x10-9 K
Noise Matching with a Realistic Readout
2D-FEM calculated optimal SQL sensitivity
1 m
1000 2000 3000 4000 5000 60001E-23
1E-22
1E-21
1E-20
Shh1/2
( Hz
-1/2
)
Frequency (Hz)
internal diameter readout K=1.7 1011 N/mwhips and slots K=1.5 108 N/m
( ) ( ) ( )/GWH X hω ω ω≡Response to a GW field h()
• Increased response (mechanical amplification) but also increased number of GW-sensitive (quadrupolar) modes. Mixture of cylinder and whips modes.
•Selective detector (by means of the test mass design, arrangement of the readout and large interrogation area)
Dual is a multimode selective detector
0 1000 2000 3000 4000 5000 60000,1
1
10
100
1000
10000
Hgw (m)
Frequency (Hz)
internal diameter readoutwhips and slots
L=2.1 m (M=7.7 tons)
0 1000 2000 3000 4000 5000 60001x10-23
1x10-21
1x10-19
Frequency (Hz)
Shh1/2
(Hz-1/2
)
0 1000 2000 3000 4000 5000 60001x10-23
1x10-21
1x10-19
Frequency (Hz)
Shh1/2
(Hz-1/2
)
Refined model: 3D FEM
2D plain strain FEM simulation 3D FEM simulation (Ansys)
3D Spurious modes not fully suppressed by selective readout
The number of spurious modes can be reduced by shortening the test mass
Sensitivity of longer-massive version can be recovered by using several short detectors (in the same cryostat) with the same overall mass.
Mo, SQL, T/Q=5x10-9, R=0.35 m
L=1.2 m (M=4.4 tons)
LR
Refined Model: 3D FEM + SQUID Readout
• Complete mechanical 3D FEM simulation
• 4 capacitive wide area transducers in series for a selective quadrupolar readout
• SQUID amplifier with low loss matching transformer
• Electrical LCtot mode tuned to the sensitivity band.
L
C
C
C
C
0 1000 2000 3000 4000 5000 60001x10-23
1x10-21
1x10-19
Frequency (Hz)
Shh1/2
(Hz-1/2
)
Electrical:T=50 mKQ=2x106
Ebias=8x107 V/mC=3 nF
Mechanical:MolibdenumR=0.35 m, L=1.19 m, M=4.4 tons T=50 mKQ=1x107
SQUID noise: 1 h
Realistic Readout
Ideal Noise Matched Readout
Ideal Readout vs Realistic Capacitive SQUID Readout