Abstract
In order to provide continuous cooling at 50 mK for space or laboratory applications, we are designing a miniature adiabatic demagnetization refrigerator (MADR) anchored at a reservoir at 5 K. Continuous cooling is obtained by the use of several paramagnetic pills placed in series with heat switches. We are aiming for a fast cycling process (≈ 500 s) in order to reduce the size of the pills. For that purpose, we developed and tested magnetoresistive heat switches based on single crystals of tungsten. They provide good thermal performance for a very short switching time, depending only on the ramping speed of the magnet used. Measurements of heat conductivity between 150 mK and 10 K with fields ranging from 0 T to 3 T are presented for different tungsten crystals. Small superconducting magnets have been designed and manufactured from high current density NbTi wires. The shielding is achieved using ferromagnetic material, and a holmium core is used as a flux concentrator. Superconducting shielding is envisioned. Results of numerical simulations and measurements of magnetic field are compared. A prototype continuous MADR, using magnetoresistive heat switches, small paramagnetic pills, and compact magnets has been tested. A design of a MADR that would provide continuous cooling below 100 mK is described.
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Duval, J.M., Cain, B.M., Timbie, P.T. (2005). Magnetoresistive Heat Switches and Compact Superconducting Magnets for a Miniature Adiabatic Demagnetization Refrigerator. In: Ross, R.G. (eds) Cryocoolers 13. Springer, Boston, MA. https://doi.org/10.1007/0-387-27533-9_71
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DOI: https://doi.org/10.1007/0-387-27533-9_71
Publisher Name: Springer, Boston, MA
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