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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