Refractive-index gas thermometry

Abstract

The principles and techniques of primary refractive-index gas thermometry (RIGT) are reviewed. Absolute primary RIGT using microwave measurements of helium-filled quasispherical resonators has been implemented at the temperatures of the triple points of neon, oxygen, argon and water, with relative standard uncertainties ranging from 9.1 × 10−6 to 3.5 × 10−5. Researchers are now also using argon-filled cylindrical microwave resonators for RIGT near ambient temperature, with relative standard uncertainties between 3.8 × 10−5 and 4.6 × 10−5, and conducting relative RIGT measurements on isobars at low temperatures. RIGT at optical frequencies is progressing, and has been used to perform a Boltzmann constant measurement at room temperature with a relative standard uncertainty of 1.2 × 10−5. Uncertainty budgets from implementations of absolute primary microwave RIGT, relative primary microwave RIGT and absolute primary optical RIGT are provided.

Resonance frequency measurement with accuracy and stability at the 10−12 level in a copper microwave cavity below 26 K by experimental optimization

“…The uncertainty contribution of pressure to measurements of thermodynamic temperature has also been reported in our previous work [1] and Fig. 2 in the review paper of RIGT [2]. To fill helium-4 gas…”

“…Single pressure refractive index gas thermometry (SPRIGT), jointly developed by Technical Institute of Physics and Chemistry of Chinese Academy of Sciences (TIPC-CAS) in China and Laboratoire national de métrologie et d'essais-Conservatoire national des arts et métiers (LNE-Cnam) in France [1], is one kind of promising polarizing gas thermometry methods. As a relative primary thermometry [2], SPRIGT measurements are conducted on single isobars rather than isotherms, it decreases the dependence on the accurate absolute pressure measurement and increases the measurement speed ten-fold. With state-of-the-art ab initio calculation of helium-4…”

“…For the reference temperature, it can be the fixed point of neon or a known thermodynamic temperature measured from other absolute primary thermometry, such as acoustic gas thermometry. In refractive index gas thermometry (RIGT) [2,5], microwave measurements are also used to get gas refractive index. Then the thermodynamic temperature is deduced from the refractive index and pressure measurements.…”

Influence of Isotopologue Dipole Moments on Precision Dielectric-Constant Measurements

“…In Eqs. (2) and (3) and the remainder of this paper, we have used the symbols p and A p for dipole-related quantities instead of the µ and Aµ used in previous work [3,5]; this is to avoid confusion with the use of µ for the magnetic permeability in refractive-index gas metrology [7]. For a mixture of n components (whether different chemical compounds or isotopologues), the average appearing in A p is given by…”

“…Additional terms of higher order in density can be added to the right-hand side of Eq. (1) [1,7], but extrapolating dielectric-constant data to zero density can yield accurate values of Aε (and thence the molecular polarizability). Alternatively, if the polarizability is known, accurate dielectric measurements can determine the molar density.…”