NRC Microwave Refractive Index Gas Thermometry Implementation Between 24.5 K and 84 K

Abstract

The implementation of microwave refractive index gas thermometry at the National Research Council between 24.5 K and 84 K is reported. A new gas-handling system for accurate control and measurement of experimental gas pressure has been constructed, and primary thermometry measurements have been taken using a quasi-spherical copper resonator and helium gas at temperatures corresponding to three defining fixed points of the International Temperature Scale of 1990 (ITS-90). These measurements indicate differences between the thermodynamic temperature T and ITS-90 temperature $T_{90}$ of $\left( T - T_{90} \right) = -0.60 \pm 0.56$ mK at $T_{90} = 24.5561$ K, $\left( T - T_{90} \right) = -2.0 \pm 1.3$ mK at $T_{90} = 54.3584$ K, and $\left( T - T_{90} \right) = -4.0 \pm 2.9$ mK at $T_{90} = 83.8058$ K. The present results at $T_{90} = 24.5561$ K and $T_{90} = 83.8058$ K agree with previously reported measurements from other primary thermometry techniques of acoustic gas thermometry and dielectric constant gas thermometry, and the result at $T_{90} = 54.3584$ K provides new information in a temperature region where there is a gap in other recent data sets.