2. Content 1 Introduction to Cryocoolers
2 Commercially available versions
Reliquefaction of Helium vapor => zero boil off
4 Integration into cryostats – options and limitations

3. Cryocoolers principle
Cooling process: φ j + × =
)/2
cos 1 ( V C W ) - a p m VW
Piston
Regenerator ò × = p 2 C dV f Q
& VC
Necessity of an additional
phase shift between p und VC

4. low temperature cryocoolers
Types of Cryocoolers
Common
types of
low temperature cryocoolers
Stirling-Cooler GM-Cooler Basic Pulse Tube v
Orifice Pulse Tube Double inlet PT Four Valve PT

5. Cooling power map
& Stirling CC

6. Commercial options at 4.2 K – Pulse Tube
PT 415, Pel=10 60 Hz
1.5 W and 65 W
@ 50 Hz

7. Commercial options at 4.2 K – Pulse Tube
SHI – Sumitomo Heavy Industries
Pel= 7 kW

8. Commercial options at 4.2 K – GM cryocooler
Gifford-McMahon Refrigerator (GM)
SHI - Sumitomo Heavy Industries
1.5 W and 50 W
@ 50 Hz
~0.5 m

9. Commercial options at 4.3 K – GM cryocooler based
SHI - Sumitomo Heavy Industries

10. Integration of cryocoolers in a cryostat / application
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

11. Inclination dependency of the performance
Cryomech PT 410

12. Background magnetic field – rotary valve motor
Specification from Cryomech: max. 100 Gauss => 10 mT ( 160 x Earth field)
Remote valve at 1m
Reduced cooling power K

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

14. Current leads – dry cooling
Application – Dry current leads
Two stage
Cryocooler
300 K flange
T<62 K for HTS leads
Heat load to the 1st stage
Copper rods RRR=10
2nd stage at 4.2 K

15. Current leads – dry cooling
PTR 415
RDK 415D

16. 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

17. Reliquefier – Pulse Tube Refrigerator based
Custom solution that needs to
be adapted to the cryostat needs.

18. Sources of perturbation
Vibrations and noise level:
Mechanical vibrations at the cold head
Temperature oscillations
Electromagnetic noise

19. Mechanical vibration by pressure oscillation

20. Spectrum of mechanical oscillations
Two stage, coaxial PTC
Analysis of the oscillation – frequency spectrum
9 µm
X direction
Z direction
0.7 µm
T2=10 K
fop=2.5 Hz
Amplitude 2nd stage in µm
Frequency in Hz

21. Comparison PT vs. GM Typical vibration at the cold tip of a PTC
Displacement in μm

22. Sources of pertubation
Vibrations and noise level:
Mechanical vibrations at the cold head
Temperature oscillations
Electromagnetic noise

23. Temperature oscillations
Two stage, coaxial PTC RV NV
PT2
PT1
Reg1
Reg2
Cool down behavior
Temperature in K
Time in h
ΔT= ± 0.2 K

24. Temperature oscillations in Helium
Temperature changes in K
Frequency in Hz

25. Sources of purtubation
Vibrations and noise level:
Mechanical vibrations at the cold head
Temperature oscillations
Electromagnetic noise

26. Heat capacities of He and regenerator materials
* Arp, Thermophysical Prop. 4He,
R. Radebaugh, NIST, Boulder,
WADD Technical Report NBoS.

27. Comparison of cooling techniques
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
Orientation dependency
Vertical cryostats are
standard
Almost independent
Loss of perform.
≤ 15 % in all directions
α ≤ 30° OK,
α > 30° not possible
Maintenance interval
Filling of the cryostat
1 to 2 days
10,000 hours
Cold unit + compr.
20,000 hours
just 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

28. Thank you for your attention.