Abstract
The persistent failure of a previous welded copper demagnetization stage to reach temperatures significantly below 100 microkelvin caused us to replace the original structure. The new stage has been machined from a single ingot of moderately high purity (4 9's) polycrystalline copper, with a much more rigid cross-section. Heat treatment increased the RRR of the copper to 4000. The cryostat is now capable of maintaining temperatures below 50 microkelvin for over a week. However there appear to be gradients between the thermometer and the copper nuclei in the main field, which may be a factor of 5 or more colder. Much of the improved performance comes from the identification and removal of an existing heat leak. The vibrational heating is dramatically smaller than that of the old stage, inferred from the magnetic field dependence of the heat leak.
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CG-OFC Copper from Hitachi Cable America Inc., 50 Main Atreet, White Plains, New York 10601 USA
Vespel SP22 from DuPont Company, Plasticts Products and Resins Dept, Vespel Parts Marketing Section, Wilmington, DE 19898 USA
Fickett, F. R. J. Phys. F12, 1753 (1982) is one of many references discussing oxygen annealing of copper.
902 Machinable Ceramic from Cotronics Corp, 3379 Shore Parkway, Brooklyn NY 11235
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Smith, E.N., Sawada, A., Pollack, L. et al. The new cornell copper demagnetization stage. J Low Temp Phys 101, 593–598 (1995). https://doi.org/10.1007/BF00753359
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DOI: https://doi.org/10.1007/BF00753359