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An Absolute Primary Thermometer

Kolloquium der Abteilung 7

An absolute primary thermometer that realizes thermodynamic temperature over a wide, perhaps many decades, temperature range has significant potential for replacing the fixed-point artifacts in the range over the range from ~230 K to 1300 K. It could also provide a better understanding thermodynamic temperature in this range of the ITS-90 temperature scale. NIST is exploring the potential of such a thermometer that exploits Johnson noise thermometry (JNT) referenced to a quantum voltage noise source (QVNS). The QVNS itself could be made very compact by fabricating the Josephson junctions with high-temperature superconductors (HTS) and integrating the HTS chip on a compact, commercially available 77 K cryocooler.

Such a thermometer would dramatically reduce the effort and space required at calibration laboratories that is currently required to support and operate many different fixed points used to maintain the ITS-90. It would also enable the direct calibration at temperatures between the fixed points that currently requires interpolation between fixed points.

We will describe progress toward development of the thermometer, present electrical characterization of the junction and QVNS circuit, and show results of the demonstrated synthesis capability of the HTS QVNS.