研究目的
To develop a novel pressure standard for helium gas based on the measurement of resonance frequencies of a superconducting cavity and ab initio calculations of the thermophysical properties of helium, aiming to significantly improve the accuracy of measurements in the range 200 Pa to 20 kPa.
研究成果
The new pressure standard based on the microwave resonance frequency measurement of a superconducting cavity and ab initio calculations should significantly improve the accuracy of pressure measurement for helium gas from 200 Pa to 20 kPa.
研究不足
The thermomolecular pressure effect poses a particular challenge. The accuracy is limited by the measurement of thermodynamic temperature and the uncertainties in the virial coefficients.
1：Experimental Design and Method Selection:
The experiment involves measuring resonance frequencies of a superconducting microwave cavity filled with helium gas and using ab initio calculations to determine the thermophysical properties of helium.
2：Sample Selection and Data Sources:
Ultra-pure, dry helium gas is used, with pressure measured by a piston balance calibrated against a primary standard.
3：List of Experimental Equipment and Materials:
A superconducting cavity made from Nb-coated copper hemispheres, a cryostat cooled to between 5 K and 7 K, PtCo and RhFe standard resistance thermometers, a mass flow controller, and a network analyser.
4：Experimental Procedures and Operational Workflow:
The resonator is cooled, helium gas is introduced, and microwave frequencies are swept over different TE and TM modes while recording the signal.
5：Data Analysis Methods:
The pressure is deduced from the refractive index and temperature measurements via ab initio calculations of dielectric virial coefficients.
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