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Status of MiniGRAILG. Frossati, A.de Waard, L.Gottardi

and O.Usenko

Kamerlingh Onnes LaboratoryLeiden, The Netherlands

ESF exploratory workshop: Toward a 3rd generation

European Gravitational Wave Observatory

Perugia, 21-23-Sept. 2005

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Advantagesof Spheres

• Large cross section compared with a traditional bar detector

• Omni-directional• Determine direction and

polarization (TIGA)• Short cool-down time• Relatively cheap• Toroidal modes could be used as

vetoes for non-GW signals.

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MiniGRAIL

Material CuAl6%Diameter = 0.68 mMass M ~ 1400 kgResonance freq. 2850/3050 HzAimed temperature ~ 20 mKQL sensitivity h~4x10-21

QL spectral amplitude ĥ~4.5x10-23

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Sensitivity

Minimum detectable energy Teff=T/Q +2TN

N B NE = k T =1 h with = 3KHz

For a SQUID noise energy of one quantum

-7NT 1.5×10 K Need~0.05; Q~2x106: T~30 mK

4.5QL -23h ×10 / Hz

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MiniGRAILInitial goal Advanced Quantum limit

EN 100 h 10 h 1 h

TN 1.510-5 1.510-6 1.510-7

Teff 4.210-5 4.210-6 4.210-7

0.1 0.1 0.1

f 224 224 230

h0 310-20 9.510-21 310-21

4.510-22 1.610-22 4.510-232/10 )( HzfSh

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MiniGRAILCryogenics

cryostat

Liquid N2 77K (-196 ºC)

Liquid He4K (-269 ºC)

Dilution refrigerator(10 mK)

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Kamerlingh Onnes LaboratoryUltra-low temperature lab

MiniGRAILcryostat

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MiniGRAILSeismic isolation

~ 50 dB

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MiniGRAILCryogenics

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Closed Membrane Capacitive Transducer

Advantages:• Compact design• Easy to make

electrode

membrane

mass (~ 200 g)spring

CuAl6%

d~30 micro mVBIAS up to 500 V

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New one or two-modes transducer

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Very low noise amplifier; 2-stage SQUID

second SQUIDfirst SQUID

transformer

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MiniGRAIL sensitivity - run 6

1.5 x 10-20

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MiniGRAIL sensitivity - run 6

Run 6T 5 K 700 ħQ 105

M 200 gC 1.1 nFVbias 200 V

Run8T 80 mK 100 ħQ 106

M 400 gC 1.5 nFVbias 300 V

Teff = 40 K4.5 x 10-22

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MiniGRAIL sensitivity - comparison

Initial target large interferometers

GEO 05

LIGO S3

NAUTILUS / EXPLORER

AURIGA

MiniGRAIL run6

MiniGRAIL expected run 8

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Run 8: resonance spectrum at 200V

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www.minigrail.nlNext: 33 ton sphere ?Project together with the Roma

group to be submitted to INFN

hQL ≈4x10-24/√Hz

hQL≈4x10-23/√Hz