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
Title
Outline
• Building blocks:Pulse tube rifrigeratorHe3 sorption coolerSIN electronic refrigeratorExperimental resultsEstimated margins, other experiments
General view of the equipment
Cryostat D300, H850
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
Pulse tube cooler & compressorSumitomo
Cryocooler SRP-052Two 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
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.
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
SPM view of SIN electron cooler
SIN cooler with Au trap
SINIS cooler
Electron cooler with trap
IV curves of SIN thermometer
-0.4 -0.2 0.0 0.2 0.4
-200
-100
0
100
200
Sen
sor
volta
ge, V
Sensor current, nA
C V
A 7 k SINIS thermometer IV curve at Tph=290 mK without cooling (X-es), and under electron cooling (circles)
Cooling curves
280 300 320 340 360 380
190
200
210
220
230
240
250
260
270
Ele
ctro
n te
mp
era
ture
, K
Phonon temperature, K
B
Electron cooling starting from phonon temperatures in the range of 287-365 mK
Ideal SIN tunnel junction IV curve
kT
eV
T
TTT
eR
kTVI c
c sinh76.1
exp11),(
The IV curve of SIN junction have simple analythic form
The electron temperature under absorbed power
Zero-bias resistance with leakage current
kT
eV
T
TTT
eR
kTVI c
c sinh76.1
exp11),(
5/15
V
PTT phe
1
76.1
6.0
)0(
s
n
c
e
T
T
n R
R
T
T
e
R
Rr
e
c
Calculated ZBR
rdsn 13
rdsn 25
rdsn 50
Tn
0 0.1 0.2 0.3 0.41
10
100
1 103
1 104
.
.
.
Resistance ratio calculated for bias voltages 0, 200, 300 V, thermometer normal resistance 10 k and leakage resistance 35 M
Dynamic resistance of SIN
-400 -300 -200 -100 0 100 200 300 400
0
10000
20000
30000
40000
50000MF355 J9/13measured 03.03.2003
Res
ista
nce,
k
Voltage, V
V0T20 V400T20 V400T250 V150T250 Theory
Dependencies of sensor resistance measured in dilution refrigerator at
20 mK & 250 mK and co ler bias 0, 150, 400 V
Optimal cooling
0 100 200 300 400 500
80
120
160
200
240
280MF355 J9/13measured 03.03.2003
Ele
ctro
n te
mpe
ratu
re,K
Cooler bias voltage, V
Electron temperature estimated from dynamic resistance at 300V (boxes)
Calculation of cooling power
Cooling power
Effective electron temperature
bN
bcool k
eVV
eeR
kP exp
2
2
5
2
5
coolbgns
PPRV
T
Heat balance
Q98 n
Q96 n
Q93 n
Q89 n
Q85 n
T250n
Tn
0 0.05 0.1 0.15 0.2 0.25
0
2 1013
4 1013
.
Curve T250 (circles) corresponds to the electron-phonon power transfer
Pep=(Tph5-Te
5)v
at 250 mK, other curves from the left to the right present cooling and heating power balance
Pv=Pcool-V2/Rs-Pbg
at bias 392, 384, 372, 356, 340 V
DiscussionObtained 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.
ConclusionWe 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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