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Present status of MiniGRAIL

Present status of MiniGRAIL. Sasha Usenko, Arlette de Waard Luciano Gottardi & Giorgio Frossati. www.minigrail.nl. MiniGRAIL. Material CuAl6% Diameter  = 0.68 m Mass M = 1400 kg Resonance freq. f = 2900 Hz. Three last runs.

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Present status of MiniGRAIL

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  1. Present status of MiniGRAIL Sasha Usenko, Arlette de Waard Luciano Gottardi & Giorgio Frossati

  2. www.minigrail.nl MiniGRAIL Material CuAl6% Diameter  = 0.68 m Mass M = 1400 kg Resonance freq. f = 2900 Hz

  3. Three last runs • Run-6: Leak DR.T=5.2K - 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.Teff~29 mK

  4. transducer design

  5. 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

  6. Run 8 overview

  7. Results @ 4K MiniGRAIL SQUIDs noise spectra SQUID 1 SQUID 3 N~2 mF0/Hz1/2 SQUID 3

  8. Results @ 4K Mode coupling and tuning curves Teff~T/βQ+2TN Run6: bmax = 6.58E-4

  9. Results @ 4K Calibration 2892 Hz mode • f=2892.854 Hz • Vwb=5.3E-13 V2/Hz • Vnb=3.23E-9 V2/Hz • G=1.64E-4 • K= 1.95E10 K/V2 Teq= 3.92 K Teff= 200 mK

  10. Results @ 4K Calibration 2892 Hz mode • f=2825.316 Hz • Vwb=5.22E-13 V2/Hz • Vnb=2.44E-9 V2/Hz • G=2.14E-4 • K= 4.5E10 K/V2 Teq= 5.3 K Teff= 310 mK

  11. Results @ 70 mK Calibration of 2892 Hz and 2825 Hz modes f=2820.44 Hz Vwb=1.4E-13 V2/Hz Vnb=1.6E-11 V2/Hz G=8.75E-3 K= 1.4E11 K/V2 Teq= 79 mK Teff = 29 mK f=2892.5 Hz Vwb=1.4E-13 V2/Hz Vnb=1.4E-11 V2/Hz G=1E-2 K= 2.6E11 K/V2 Teq= 2 K Teff = 800 mK

  12. Preparing for next run

  13. 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 dampingmass, allowing to run MiniGRAIL incomplete 6transducer configuration.

  14. 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 earth’s and stray magnetic fields • Use cold RF filters on all squid cables. RF filters on SQUID cables Radiation shields and the last copper mass arelead plated and covered with mju-metal tape

  15. No glasmet-shielding Glasmet-shielding

  16. New transducer design The transducers werecompletelyredesigned in order to increase the area and to improve thepolishing of the surfaces. This was obtained by using acentral fixing bolt instead of 8 bolts on the perimeter. A 10 umplastic foil is placed on the mass and theelectrode isplaced freely on it and glued to the central post with lowcontraction epoxy glue. The capacitance of the 12 cmdiameter transducer is typically 5 nF, a factor 5 better thanthe old one. Old design : C~1 nF New design: C~ 5 nF

  17. 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.

  18. SQUID developments Because of problems with DROS operation at mK temperatureswe replaced it with a flux transformer DCSQUID, designed at the Twente University.

  19. Kamerlingh Onnes LaboratoryUltra-low temperature lab MiniGRAIL cryostat

  20. Kamerlingh Onnes LaboratoryUltra-low temperature lab-(ex?)

  21. 5e-20Hz-1/2 on 30 Hz band With 700ћ at 5K Expected (70 ћ at 0.05K) ~5e-22Hz-1/2 on 300Hz band Quantum limit

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