STREGA - WP2-Task C: Design of advanced cryogenic suspensions
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Transcript of STREGA - WP2-Task C: Design of advanced cryogenic suspensions
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Participants:
C-1:Cryogenic last-stage suspensions (interferometers) (F.Ricci-G.Frossati)Objectives: -Design new suspension elements for the last stage of interferometers.-Achieve a low noise remote control of the mirror position using cryogenic sensors-Assemble and test of a full-scale prototype of cryogenic final stage C-2:Cryogenics suspensions for advanced interferometers (G.Frossati-M.Bassan)-Objectives:-Two 1.2 ton spheres with their suspension assembled and measurementsof Q and thermal noise at low temperature performed.C-3: Cryogenics suspension system for interferometers (S.Braccini-M.Bassan)Objectives:-The entire apparatus be located in a cryogenic environment; the extra noise coming from the cryogenic system be studied and made negligible.-Full cryogenic suspension be assembled and tested
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Participants:Participants: INFN ROG
Leiden University
Tasks: - Cool down of Minigrail to 50 mK- Investigation of heat transfer from the mixing chamber to the sphere
Deliverables: - Report on mechanical transfer function
measurements of cryogenic suspension
Cryogenic suspension system for advanced resonant detectors
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MiniGRAILCryogenics
cryostat
Liquid N2 77K (-196 ºC)
Liquid He4K (-269 ºC)
Dilution refrigerator(10 mK)
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MiniGRAILCryogenics; The dilution refrigerator
still(700 mK)
50 mKplate
mixingchamber(10 mK)
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To 50 mK shield
To mixing chamber
CryogenicsThermal anchoring suspension
To still shield
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CryogenicsRun 4
Minimum temperatures:Tsphere = 80 mKTmc = 20 mK
Time dependent heat leak from sphere:
45 W after 6 weeks
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Vibration Isolation System
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7Attenuation cables
+ absorbers
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Vibration Isolation System
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Attenuation between mass 1 and 2
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• Larger diameter (68 cm instead of 65 cm) gives lower frequency and higher mass (1300 kg instead of 1150 kg).
• Six holes machined in TIGA positions
The new sphere
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Resonance frequencies of bare sphere at 300 K
Old sphereNew sphere
Frequency of new sphere about 200 Hz lower
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Improvements on the Vibration Isolation System
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Material before (mm) fbefore (Hz)
CuAl 1,2 370 3516
CuAl 3,4 370 3516
Cu 5-7 370 3397
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Improvements on the Vibration Isolation System
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Material before (mm) fbefore (Hz) after (mm) fafter (Hz)
CuAl 1,2 370 3516 370 3516
CuAl 3,4 370 3516 362 3633
Cu 5-7 370 3397 358 3512
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Improvements on the Vibration Isolation System
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~ 50 dB
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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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Cryogenic run
transformer +2-stage SQUID
calibrator
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3 hour acquisition @ 5K of mode 3 (2943 Hz)
exponential fit
Teff = 70 mK
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MiniGRAIL sensitivity - run 6
1.5 x 10-20
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MiniGRAIL sensitivity - run 6
Run 6
T 5 K
700 ħ
Q 105
M 200 g
C 1.1 nF
Vbias 200 V
Run 7
T 80 mK
100 ħ
Q 106
M 400 g
C 1.5 nF
Vbias 400 V
Teff = 40 K4 x 10-22
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MiniGRAIL sensitivity - comparison
Initial target large interferometers
LIGO S3
GEO
AURIGA
NAUTILUS/EXPLORER
MiniGRAILrun 6
Planned at the end of 2004
MiniGRAILrun 7