Present status of MiniGRAIL

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Present status of MiniGRAIL

• Sasha Usenko, Arlette de Waard
• Luciano Gottardi Giorgio Frossati

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MiniGRAIL
www.minigrail.nl
Material CuAl6 Diameter ? 0.68 m Mass M
1400 kg Resonance freq. f 2900 Hz
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Three last runs

• Run-6 Leak DR. T5.2K - Strain sensitivity
  5x10-20 on 30 Hz bandwidth. Teff 200 mK
• Run 7- Leak-IVC-OVC-Stopped
• Run 8- Reached 60 mK. Thermally excited peaks at
  60 mK were too low due to poor SQUID stability
  and too large transducer mass.Teff29 mK

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transducer design
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MiniGRAIL DAQ system overview

• Fast DAQ
• Using 24 bit 8 channel sigma-delta converter (NI
  4472-PCI) (one channel is used for GPS timing)
• GPS system Trimble Accutime 2000 (accuracy /-
  25 ppm)
• Acquisition frequency 18642 Hz
• Data rate 73 KB/s (262 MB/h) per channel (6
  GB/day)
• Slow DAQ
• Using 16 bit 6 channel AD converter (NI 4472-PCI)
• Acquisition frequency 10 Hz

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Run 8 overview
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Results _at_ 4K
MiniGRAIL SQUIDs noise spectra
SQUID 1
SQUID 3
N2 mF0/Hz1/2
SQUID 3
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Results _at_ 4K
Mode coupling and tuning curves
TeffT/ßQ2TN
Run6 bmax 6.58E-4
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Results _at_ 4K
Calibration 2892 Hz mode

• f2892.854 Hz
• Vwb5.3E-13 V2/Hz
• Vnb3.23E-9 V2/Hz
• G1.64E-4
• K 1.95 E10 K/V2

Teq 3.92 K Teff 200 mK
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Results _at_ 4K
Calibration 2892 Hz mode

• f2825.316 Hz
• Vwb5.22E-13 V2/Hz
• Vnb2.44E-9 V2/Hz
• G2.14E-4
• K 4.5E10 K/V2

Teq 5.3 K Teff 310 mK
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Results _at_ 70 mK
Calibration of 2892 Hz and 2825 Hz modes
f2820.44 Hz Vwb1.4E-13 V2/Hz Vnb1.6E-11
V2/Hz G8.75E-3 K 1.4E11 K/V2 Teq 79 mK
Teff 29 mK
f2892.5 Hz Vwb1.4E-13 V2/Hz Vnb1.4E-11
V2/Hz G1E-2 K 2.6E11 K/V2 Teq 2 K Teff
800 mK
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Preparing for next run
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MiniGRAIL improvements
New dilution refrigerator
New smaller transformer boxes
A new dilution refrigerator unit with larger
mixing chamber and heat exchangers.Expected
cooling power of 50 uW at 30 mK.
6 boxes can now fit easily on the last damping
mass, allowing to run MiniGRAIL in complete 6
transducer configuration.
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improvements

• Improved shielding
• Tin/lead plated radiation shields and first
  copper mass.
• Wrapped shields with a m-metal to shield the
  sphere and the squids from earths and stray
  magnetic fields
• Use cold RF filters on all squid cables.

RF filters on SQUID cables
Radiation shields and the last copper mass are
lead plated and covered with mju-metal tape
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No glasmet-shielding Glasmet-shielding
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New transducer design
The transducers were completely redesigned in
order to increase the area and to improve the
polishing of the surfaces. This was obtained by
using a central fixing bolt instead of 8 bolts on
the perimeter. A 10 um plastic foil is placed on
the mass and the electrode is placed freely on it
and glued to the central post with low
contraction epoxy glue. The capacitance of the 12
cm diameter transducer is typically 5 nF, a
factor 5 better than the old one.
Old design C1 nF New design C 5 nF
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SQUID developments
When the SQUID is coupled to a high Q resonant
load the cold damping network greatly improves
the system stability (AURIGA).
Old system
New system
Operating without cold damping by reducing
transformer Q was not successful.
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SQUID developments
Because of problems with DROS operation at mK
temperatures we replaced it with a flux
transformer DC SQUID, designed at the Twente
University.
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Kamerlingh Onnes LaboratoryUltra-low temperature
lab
MiniGRAIL cryostat
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Kamerlingh Onnes LaboratoryUltra-low temperature
lab-(ex?)
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5e-20Hz-1/2 on 30 Hz band With 700? at 5K
Expected (70 ? at 0.05K) 5e-22Hz-1/2 on 300Hz
band
Quantum limit