1. xkcd

2. Cryogenics Tyler Brewer

3. Overview History of cryogenics Uses Methods of Cooling Materials Considerations Vibration Issues

4. History “Cryogenics” is for approximately < ~150 C Greek –“Kryos” = frost –“-genic” = to produce 1887: Liquid oxygen produced (-183 C, 90K) 1892: Dewar invents the vacuum flask 1908: Liquid helium produced (4.2K) –Superconductivity discovered in 1911 thanks to this 1960: 1*10^-6 K attainable Photo: The Worlds of David Darling

5. Industrial Uses Liquefied Natural Gas (LNG) Liquid Hydrogen / Oxygen rocket fuel Medicine –Cryosurgery –Medical gases like O 2 Superconductivity –LHC at CERN Food preservation Manufacturing –Tight-tolerance part fitting Electronics –Detectors –Reduced thermal noise Photo: CIMS Gas Products, LLC

6. Mechanics of Cooling Recuperative cycles –Gas is passed through heat exchanger to transfer energy –Continuous heat transfer Regenerative cycles –Cyclic process with low temperature stored in “Regenerator” –Requires large heat capacity due to alternating flow Photo: European Space Agency

7. Joule-Thompson Liquifier Requires gas to be < 40 K AKA Linde-Hampson Effect 1.Gas compressed 2.Gas precooled 3.Gas passed through J-T valve (cools down even more) 4.Gas liquid at lowest pressure and temp, removes heat from cold head 5.“Exhaust” gas recycled to precool incoming gas, sent back to reservoir

8. Hybrid Cascade JT cooler P ~ 3 kPa ~ 0.01 atm

9. Other Regenerative Methods Claude Liquefier –3 heat exchangers with expansion engine Collins Cycle –Commonly used for mass production of cryo-liquids –Complicated version of Claude liquifier

10. Stirling Cycle Refrigerator Evolved from Stirling heat engine working in reverse 1.He compressed in upper chamber, hot 2.Displacer moves up, forcing He through Regenerator 3.Displacer and Compressor move up, isothermal expansion in lower chamber (extracts heat from R) 4.D and C move down, forcing He through R (removes more heat from R)

11. Gifford-McMahon Cycle Similar to Stirling cycle, but with cycling valves 1.Outlet valve closed, inlet valve opens, high pressure He fills R and space above D 2.Displacer moves up, gas passes through R, cooled isobarically 3.Inlet closes, outlet opens, gas expands, removes heat 4.D returns to initial position, gas warms isobarically

12. Considerations Temporary or long-term use Owning and operating cost Overall size Purchase liquid He, vent exhaust vapors –Small scale Purchase gaseous He, liquefy it, vent the exhaust –Depends on care and efficiency of system Purchase gaseous He, liquefy it, recover exhaust for reuse –Depends on care and efficiency of system Purchase gaseous He, run in closed-cycle refrigerator –More expensive startup

13. Magnetocaloric Effect When removed from a magnetic field, molecules become disorderly If isolated, energy to shift orientation comes from phonon collisions Results in reduced temperature Can attain < 1 K using this technique in small scales Gadolinium Photo: Wikipedia

14. Properties of Materials Heat capacity changes as T → 0 K Phonons contribute to heat capacity at low T Electron flow contributes to energy, besides classical resistance, < 10 K Thermal contraction, ~1% of dimension –Thermal stress, tolerance considerations, coupling Electrical Resistivity –Lowest resistivity depends on lattice structure, purity

15. Properties of Materials Thermal conductivity –Nonlinearly dependent on T Lattice structures shift Mechanical properties: –Stress –Strain –Elasticity Superconductivity

16. Common Issues Vibrational travel up to 60 μm depending on hardware –Active vibration damping –System isolation –Montana Instruments: <5 μm Frost buildup –Design cold head so sample is warmest object in the chamber Photo: Montana Istruments

17. Questions

18. Sources Brittanica: http://www.britannica.com/science/cryogenicshttp://www.britannica.com/science/cryogenics CIMS Gas Products, http://www.cimsgas.com/cryogenics.htmlhttp://www.cimsgas.com/cryogenics.html Comic: http://xkcd.com/989/http://xkcd.com/989/ Cooltech Applications, http://www.cooltech-applications.com/magnetic-refrigeration- principle.htmlhttp://www.cooltech-applications.com/magnetic-refrigeration- principle.html David Darling: http://www.daviddarling.info/encyclopedia/D/dewar_flask.htmlhttp://www.daviddarling.info/encyclopedia/D/dewar_flask.html ESA: http://sci.esa.int/jwst/46831-cryocooler-for-miri/http://sci.esa.int/jwst/46831-cryocooler-for-miri/ Montana Instruments: http://resources.montanainstruments.com/help/article/link/vibrations Van Sciver, Steven W., Helium Cryogenics, 2 nd Ed., Springer (2012) Wikipedia: https://en.wikipedia.org/wiki/Magnetic_refrigerationhttps://en.wikipedia.org/wiki/Magnetic_refrigeration