Realization of the ~3He Vapor-Pressure Temperature Scale and Development of a Liquid-He-Free Calibration Apparatus

摘要

The ~3He vapor-pressure temperature scale was realized using an apparatus based on a continuously operating ~3He cryostat at the National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST). The cryostat has two operational modes: a ~3He circulation mode and a 1 K pot mode. The ~3He circulation mode can be used for ~3He vapor-pressure measurements below 1.6 K, and the 1 K pot mode can be used for measurements above 1.3 K. Either mode can be selected for measurements from 1.3 K to 1.6 K. The realization of the ~3He vapor-pressure temperature scale in this study fully covers its defined temperature range from 0.65 K to 3.2 K in the International Temperature Scale of 1990. The latest realization results are presented in this article. In addition, a liquid-He-free calibration apparatus was developed. It does not require liquid helium as a cryogen, which usually entails cumbersome handling and periodic refilling. The apparatus was designed for the calibration of capsule-type resistance thermometers from 0.65 K to 24.5561 K (the triple point of neon). The cooling system of the apparatus consists of a commercially available pulse-tube refrigerator and a ~3He Joule-Thomson (JT) cooling circuit developed at NMIJ/AIST. The pulse-tube refrigerator is used in a pre-cooling stage and cools the apparatus to approximately 5 K. The ~3He JT cooling circuit is used to cool the apparatus from 5 K to below 0.65 K. Since the ~3He JT cooling circuit is a closed circuit, the apparatus can run continuously with only simple maintenance required. The basic characteristics of the apparatus are described.