Construction and Start-up of a Large-Volume Thermostat for Dielectric-Constant Gas Thermometry

A liquid-bath thermostat with a volume of about 800 L was designed to provide a suitable thermal environment for a dielectric-constant gas thermometer (DCGT) in the range from the triple point of mercury to the melting point of gallium. In the paper, results obtained with the unique, huge thermostat without the DCGT measuring chamber are reported in order to demonstrate the capability of controlling the temperature of very large systems at a metrological level. First tests showed that the bath together with its temperature controller provide a temperature variation of less than ±0.5 mK peak-to-peak. This temperature instability could be maintained over a period of several days. In the central working volume (diameter 500 mm, height 650 mm), in which the vacuum chamber containing the measuring system of the DCGT will be placed later, the temperature inhomogeneity has been demonstrated to be also well below 1 mK.