Performance of a Cryocooled Nb DC Programmable Voltage Standard at 4 K
Robert J. Webber, Charles J. Burroughs, Masoud Radparvar
We report on the performance of a 1 Volt DC programmable Josephson voltage standard (PJVS) operating on a commercially available Gifford-McMahon (G-M) cryocooler at 4 K. The NIST-fabricated niobium superconductor-normal metal-superconductor (SNS) junction chip has been shown to operate successfully as integrated with this cryopackage, generating 1.229 V at the maximum operating frequency of 19.364 GHz with Shapiro steps at constant voltage which are flat to within <100nV. Because of the large operating margin (>1mA), these steps were highly stable and immune from noise. Differences in behavior of the PJVS in liquid helium (LHe) and on the cryocooler are discussed. This demonstration paves the way towards automated warming and cooling of the Josephson device and a fully automated voltage standard system.
IEEE Transactions on Applied Superconductivity
cryocooler, dc voltage, Josephson voltage standard, SNS Josephson junctions