Relative acoustic gas thermometry setup for low temperature range from 4,2 to 80 K

Relative acoustic gas thermometry setup is described. Described setup was developed and tested in VNIIFTRI. The setup is designed for the measurement of thermodynamic temperature in low temperature range down to 4,2 K. Main part of the setup is resonator with reduced cavity diameter. Reduction of resonator dimension lead to several times reduction of cooled parts of the setup with respect to the setup previously developed in VNIIFTRI. This decreases liquid nitrogen and liquid helium consumption required for cooling of resonator. Moreover, reduction of the mass of cooling parts reduces time required for temperature stabilization and thus measurement time. In the work the tests’ results of operation of main parts of the setup are presented.

Acoustic and microwave tests in a cylindrical cavity for acoustic gas thermometry at high temperature

Relative primary acoustic gas thermometry (AGT) determines the ratios of thermodynamic temperatures from measured ratios of acoustic and microwave resonance frequencies in a gas-filled metal cavity on isotherms of interest. When measured in a cavity with known dimensions, the frequencies of acoustic resonances in a gas determine the speed of sound, which is a known function of the thermodynamic temperature T . Changes in the dimensions of the cavity are measured using the frequencies of the cavity's microwave resonances. We explored techniques and materials for AGT at high temperatures using a cylindrical cavity with remote acoustic transducers. We used gas-filled ducts as acoustic waveguides to transmit sound between the cavity at high temperatures and the acoustic transducers at room temperature. We measured non-degenerate acoustic modes in a cylindrical cavity in the range 295 K< T <797 K. The fractional uncertainty of the measured acoustic frequencies increased from 2×10 −6 at 295 K to 5×10 −6 at 797 K. In addition, we measured the frequencies of several transverse magnetic (TM) microwave resonances up to 1000 K in order to track changes in the cavity's length L and radius R . The fractional standard deviation of the values of L deduced from three TM modes increased from 3×10 −6 for T <600 K to 57 × 10 −6 at 1000 K. We observed similar inconsistencies in a previous study.