Electric cooling from room temperature down to 200 mK

1
Title
Electric cooling from room temperature down to
200 mK M.Tarasov, L.Kuzmin, and I.Agulo,
Chalmers University of Technology, S41296,
Göteborg, Sweden V.Mikheev, P. Noonan, and A.
Adams Oxford Instruments Superconductivity, Old
Station way, Eynsham Witney OX29 4TL, UK
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Outline

• Building blocks
• Pulse tube rifrigerator
• He3 sorption cooler
• SIN electronic refrigerator
• Experimental results
• Estimated margins, other experiments

3
General view of the equipment
Cryostat D300, H850
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View of the He3 sorb

• View of the internal part of the cryostat
  Oxford Instruments? with He3 sorption cooler,
  removed outer vacuum can (OVC), and removed
  radiation shields

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Pulse tube cooler compressorSumitomo?
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Cryocooler SRP-052

• Two stage pulse tube cryorefrigerator
• Cold head unit RP-052A1
• First stage 20 W at 45 K, second stage 0.5W at 4K
• Compressor unit CSW-71D, water cooled 7 l/min,
• W450, L500, H687 mm, 120 kg,
• Electrical requirement 3 phase 9kVA
• Operation pressure 25 bar, steady-state 17 bar

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Top of the cryostat
To reduce interference and noise from grounding
we placed our room-temperature battery feed
electronics at the top of the cryostat close to
the connectors.
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Electron cooler chip layout

• 4 junction structure for cooling/heating at the
  top and botton
• Log-periodic antenna for 0.1-2 THz range
• Double-dipole antenna for 600 GHz
• Double-dipole antenna for 300 GHz

9
SPM view of SIN electron cooler
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SIN cooler with Au trap
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SINIS cooler
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Electron cooler with trap
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IV curves of SIN thermometer
A 7 kW SINIS thermometer IV curve at Tph290 mK
without cooling (X-es), and under electron
cooling (circles)
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Cooling curves
Electron cooling starting from phonon
temperatures in the range of 287-365 mK
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Ideal SIN tunnel junction IV curve
The IV curve of SIN junction have simple
analythic form The electron temperature under
absorbed power Zero-bias resistance with leakage
current
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Calculated ZBR
Resistance ratio calculated for bias voltages 0,
200, 300 mV, thermometer normal resistance 10 kW,
and leakage resistance 35 MW
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Dynamic resistance of SIN
Dependencies of sensor resistance measured in
dilution refrigerator at 20 mK 250 mK and co
ler bias 0, 150, 400 mV
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Optimal cooling
Electron temperature estimated from dynamic
resistance at 300mV (boxes)
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Calculation of cooling power
Cooling power Effective electron
temperature
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Heat balance
Curve T250 (circles) corresponds to the
electron-phonon power transfer Pep(Tph5-Te5)Sv a
t 250 mK, other curves from the left to the right
present cooling and heating power balance
PvPcool-V2/Rs-Pbg at bias 392, 384, 372, 356,
340 mV
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Discussion

• Obtained cooling down to 190 mK has a reserve of
  improvement down to 100 mK as in He4 liquid
  precooled He3 sorption cooler
• We are still suffering from electric noise coming
  from high power supply line and its grounding
  directly to the cryostat via high pressure supply
  from connector
• Acustic vibrations also affect operation of
  electron cooler and cold electron bolometer
• Operation wth a pulse tube refrigerator at 3.5 K
  instead of 2.8 significantly prolongs the
  precooling period and available lowest
  temperature is 290 mK instead of 275 mK.

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Conclusion
We have demonstrated the first cryogen-free
electric cooling from room temperature down to
electron temperature below 200 mK. The key idea
behind this device is to develop a millikelvin
range cryocooler as simple in operation as a
conventional kitchen refrigerator. It does not
need filling with any cryogen liquid and you need
just to switch it on in the evening to have
electron temperature of the sample below 200 mK
in the morning. The first building block of the
device is a double-stage pulse tube cryocooler
Sumitomo? that provides cooling down to 3 K.
The second building block is He3 sorption cooler
of original design by Oxford Instruments? that
brings for moderate thermal load a basic
temperature of about 280 mK. The third building
block is a Superconductor-Insulator-Normal metal
(SIN) electron cooler. This type of cooler is
analogous to the Peltier effect and in general
can provide electron cooling by up to 200 mK. In
our very first tests of the whole system we
already achieved cooling down to 191 mK.
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24
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