Abstract
The recent shortage and increasing cost of liquid helium provides motivation for cryogen-free operation of superconducting devices such as NIST programmable Josephson voltage standard (PJVS) systems. However, operation on closed-cycle cryocoolers must not compromise the performance of the PJVS system. New cryogenic packaging and cryostat integration are presented that have been optimized for the NIST 10 V PJVS, demonstrating improved attenuation of coldhead temperature oscillations, and improvement of thermal conductances in the junction-to-coldhead path. When combined with an improved design of 10 V PJVS devices employing Nb/Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> /Nb junctions with increased operating margins, we have operated a NIST PJVS at 10 V with over 1.32 mA current margins on a nominal 200 mW cryocooler using a 3.0 kW water-cooled compressor. The new cryo-package, in conjunction with the improved generation of chips, eliminates the need for liquid cryogens in applications using NIST 10 V PJVS systems.
Published Version
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