Primary Dielectric-Constant Gas Thermometry in the Range from 2.4 K to 26 K at PTB

Abstract

New dielectric-constant gas-thermometry (DCGT) measurements were performed at PTB from 2.4 K to 26 K in order to establish a temperature scale with reduced uncertainty. The progress concerning the measurement of capacitance changes, temperature, and pressure compared with the results published in 1996 is described. This is the first step on the way to determine the Boltzmann constant at the triple point of water. At more than 20 temperatures, isotherms were measured and evaluated performing both single-and multi-isotherm fits. Based on this evaluation, a more accurate DCGT scale has been established that is compared with the constant-volume gas-thermometry scale NPL-75, being one basis of the International Temperature Scale of 1990. Coincidence has been found within only a few tenths of a millikelvin above 3.3 K. This gives, together with literature data, confidence with respect to thermodynamic temperature at this level. Emphasis is also given to the results obtained for the virial coefficients, especially below 3.3 K, where the 1996 DCGT results show strong deviations from the expected behavior. The new experimental data for the second virial coefficient are compared with ab initio calculations.

Dielectric-Constant Gas-Thermometry Scale from 2.5 K to 36 K Applying 3He, 4He, and Neon in Different Temperature Ranges

“…Uncertainty budgets for thermodynamic temperature values obtained with helium applying DCGT from 2.4 K to 26 K have been published in [2,12]. Besides minor changes in estimating some uncertainty components, the most important change in the new budgets around and above 26 K occurred due to the fact that the components resulting from testing the use of different temperature expansions for the virial coefficients in a multi-isotherm fit became smaller.…”

“…The basic idea of DCGT [11], more extensively discussed in [1,2,12], is to replace the density in the equation of state of a gas with the dielectric constant, ε, and to measure it by incorporating a capacitor in the gas bulb. The dielectric constant of an ideal gas is given by the relation ε = ε 0 + α 0 N/V , where ε 0 is the exactly known electric constant, α 0 is the static electric dipole polarizability of the particles, and N/V is the number density, i.e., the equation of state of an ideal gas can be written in the form p = kT (ε − ε 0 )/α 0 .…”

“…The experimental setup of the present DCGT has been described in detail in [2]. Only slight changes concerning the thermometric setup have been performed.…”

“…The two generations of DCGT led to results for the thermodynamic temperature between 2.5 K and 27 K [1][2][3] with a standard uncertainty of a few tenths of a millikelvin in the whole range. Whereas the main goal of the first generation was to check the existing thermodynamic C. Gaiser (B) · B. Fellmuth · N. Haft Physikalisch-Technische Bundesanstalt, Abbestr.…”

“…[2][3][4][5][6][7][8][9][10][11][12]10587 Berlin, Germany e-mail: christof.gaiser@ptb.de temperature data with an independent method, the second generation was used for an efficiency test to demonstrate that DCGT is capable of determining the Boltzmann constant at the triple point of water (TPW) [4]. Compared with [2,5], the benefit of the extension of the DCGT temperature scale to 36 K presented in this article is threefold. Primarily, the existing thermodynamic temperature data above 27 K are inconsistent and, therefore, new measurements are strongly recommended to allow a clarification [6].…”