Content

1 Introduction to Cryocoolers

2 Commercially available versions

3 Reliquefaction of Helium vapor => zero boil off

4 Integration into cryostats – options and limitations

2

Content

Cooling process:

Vk

Vw

Kolben

Regenerator

RegeneratortemperaturTkTw

Ort

j+×= )/2cos1(0VVC

WC VVV +=0

)cos1( j×-×= app m

ò×=p2

0

CdVpfQ&

Necessity of an additionalphase shift between p und VC

VC

VW

φ

Pis

ton

Reg

ener

ator

3

Cryocoolers principle

Stirling-Cooler GM-Cooler Basic Pulse Tube

Orifice Pulse Tube Double inlet PT Four Valve PT

4

v

Types of Cryocoolers

Common types of

low temperature cryocoolers

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& Stirling CC

Cooling power map

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25 35 45 55 65 752

3

4

5

6

84W63W42W21W0 W3.0W

2.5W

2.0W

1.5W

1.0W

0.5W

SE

CO

ND

ST

AG

E T

EM

PE

RA

TU

RE

, K

FIRST STAGE TEMPERATURE, K

CRYOMECH TEST

0 W

PT 415, Pel=10 kW @ 60 Hz

Commercial options at 4.2 K – Pulse Tube

1.5 W and 65 W@ 50 Hz

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SHI – Sumitomo Heavy Industries

Pel= 7 kW

Commercial options at 4.2 K – Pulse Tube

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Gifford-McMahon Refrigerator (GM)SHI - Sumitomo Heavy Industries

1.5 W and 50 W@ 50 Hz

Commercial options at 4.2 K – GM cryocooler

~0.5 m

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Commercial options at 4.3 K – GM cryocooler based

SHI - Sumitomo Heavy Industries

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• Inclination angle of the cold head

• Influence of magnetic field on the performance => driving motor and regenerator

• Current lead cooling 300 K to 60 K and to 4.2 K

• Zero boil off cryostats – reliquefaction of Helium vapor using a cryocooler

• Vibrations and noise => sources of perturbations

Integration of cryocoolers in a cryostat / application

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Cryomech PT 410

Inclination dependency of the performance

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Background magnetic field – rotary valve motor

Specification from Cryomech: max. 100 Gauss => 10 mT ( 160 x Earth field)

Remote valve at 1m

Reduced cooling power1.35 W @ 4.2 K

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Background magnetic field

From: T. Morie, Experimental investigation of cooling capacity of 4K GM cryocoolers in magnetic fields, Poster ICEC 25 Twente

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Application – Dry current leads

Heat load to the 1st stage

Copper rods RRR=10

300 K flange

T<62 K for HTS leads

2nd stage at 4.2 K

Two stageCryocooler

Current leads – dry cooling

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Current leads – dry cooling

RDK 415DPTR 415

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Reliquefier – PT cryocooler based

Source: Cryomech Inc.Using a PT415 pulse tube refrigerator as reliquefier liquefaction rate from ambient 16 L/day equiv. to 0.5 W

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Reliquefier – Pulse Tube Refrigerator based

Custom solution that needs to be adapted to the cryostat needs.

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Vibrations and noise level:

• Mechanical vibrations at the cold head

• Temperature oscillations

• Electromagnetic noise

Sources of perturbation

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Mechanical vibration by pressure oscillation

T2=10 K

fop=2.5 Hz

Two stage, coaxial PTC

Frequency in Hz

Am

plitu

de 2

nd s

tage

in

µm

X directionZ direction

Analysis of the oscillation – frequency spectrum

0.7 µm

9 µm

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Spectrum of mechanical oscillations

Dis

plac

emen

t in

μ

m

Dis

plac

emen

t in

μ

m

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Typical vibration at the cold tip of a PTCComparison PT vs. GM

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Vibrations and noise level:

• Mechanical vibrations at the cold head

• Temperature oscillations

• Electromagnetic noise

Sources of pertubation

RV

NV

PT2

PT1

Reg1

Reg2

Two stage, coaxial PTCTe

mpe

ratu

re in

K

Time in h

Cool down behavior

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Temperature oscillations

ΔT= ± 0.2 K

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10-8

10-7

10-6

10-5

10-4

10-3

0.1 1 10 100 1000

** including slam the door -T= 9.2 e-4 slam the window-T= 6.3 e-4 car on street -T= 7.8 e-5

(measured byDr. Reichmann 1985)

T due to barometricpressure changes **

resonances in the space of small cavities

shuttle of helium in dewar

unmoved he-dewar with heat supply

unmoved heliumdewar

lg f / Hz

lg

T /

K

Temperature Fluctuations in Liquid-Helium

Temperature oscillations in Helium

Tem

pera

ture

cha

nges

in K

Frequency in Hz

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Vibrations and noise level:

• Mechanical vibrations at the cold head

• Temperature oscillations

• Electromagnetic noise

Sources of purtubation

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Heat capacities of He and regenerator materials

* Arp, Thermophysical Prop. 4He, R. Radebaugh, NIST, Boulder, WADD Technical Report NBoS.

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Property Liquid helium GM Cryocooler Pulse Tube Cryocooler

Mech. vibration

Small: atmospheric pressure changes

≤ 2 g (≤ 20 μm) Typical 1/10 of GM

Temperature oscillation

In mK range: related to atmospheric pressure changes

Occur below 30 K,± 0.2 K

Occur below 30 K,± 0.2 K

Orientation dependency

Vertical cryostats arestandard

Almost independent Loss of perform. ≤ 15 % in all directions

α ≤ 30° OK, α > 30° not possible

Maintenance interval

Filling of the cryostat1 to 2 days

10,000 hoursCold unit + compr.

20,000 hoursjust the compressor

Warm-up & cool-down issue

Easily ~ 1 day 1 h to 4.2 K=> decreasing maintenance interval

1.5 h to 4.2 K

No problem

Handling Needs training Easy Easy

Comparison of cooling techniques

Thank you for your attention.

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