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

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

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

Cooling power map & Stirling CC

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

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

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

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

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

Inclination dependency of the performance Cryomech PT 410

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 1.35 W @ 4.2 K

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

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

Current leads – dry cooling PTR 415 RDK 415D

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

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

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

Mechanical vibration by pressure oscillation

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

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

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

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

Temperature oscillations in Helium Temperature changes in K Frequency in Hz

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

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

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

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