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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