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A Robust Cooling Platform for NIS Junction Refrigeration and sub-Kelvin Cryogenic Systems


Recent advances in Normal metal–insulator-superconductor (NIS) tunnel junctions (Clark et al. Appl Phys Lett 86: 173508, 2005, Appl Phys Lett 84: 4, 2004) have proven these devices to be a viable technology for sub-Kelvin refrigeration. NIS junction coolers, coupled to a separate cold stage, provide a flexible platform for cooling a wide range of user-supplied payloads. Recently, a stage was cooled from 290 to 256 mK (Lowell et al. Appl Phys Lett 102: 082601 2013), but further mechanical and electrical improvements are necessary for the stage to reach its full potential. We have designed and built a new Kevlar suspended cooling platform for NIS junction refrigeration that is both lightweight and well thermally isolated; the calculated parasitic loading is \(<\!\!300\) pW from 300 to 100 mK. The platform is structurally rigid with a measured deflection of 25 \(\upmu \)m under a 2.5 kg load and has an integrated mechanical heat switch driven by a superconducting stepper motor with thermal conductivity G \( = 4.5 \times 10^{-7}\) W/K at 300 mK. An integrated radiation shield limits thermal loading and a modular platform accommodates enough junctions to provide nanowatts of continuous cooling power. The compact stage size of 7.6 cm \(\times \) 8.6 cm \(\times \) 4.8 cm and overall radiation shield size of 8.9 cm \(\times \) 10.0 cm \(\times \) 7.0 cm along with minimal electrical power requirements allow easy integration into a range of cryostats. We present the design, construction, and performance of this cooling platform as well as projections for coupling to arrays of NIS junctions and other future applications.

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This study was supported in part by the NASA APRA program.

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Correspondence to B. Wilson.

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Wilson, B., Atlas, M., Lowell, P. et al. A Robust Cooling Platform for NIS Junction Refrigeration and sub-Kelvin Cryogenic Systems. J Low Temp Phys 176, 243–248 (2014).

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  • NIS Junctions
  • Cryogenics
  • Thermal isolation