On the design and implementation of a novel impedance chamber based variable temperature regulator at liquid helium temperatures

Abstract

A novel variable temperature regulator (VTR) based on the use of a fine impedance capillary to control the flow rate of cold helium gas into the VTR chamber is described. The capillary has a diameter of just 200 μ m and the flow rate of cold Helium gas through the capillary can be effectively controlled to the desired value by heating the capillary to a preset temperature and by controlling the pressure in the VTR chamber to a preset pressure using automated control circuits. Excellent temperature stability (about±1 mK at 10 K and ±2 mK at 100 K) has been demonstrated in this setup with uniform rates of heating or cooling by an optimal choice of parameters. Compared to the more conventional VTR designs based on the use of mechanical long stem valves in the liquid Helium reservoir to control the flow rate of liquid helium into the VTR chamber, and the use of a needle valve at the top of the cryostat to control the exchange gas pressure in the thermal isolation chamber, the present design enables temperature stability at any user desired temperature to be attained with uniform rates of cooling/heating with minimum consumption of liquid Helium. The VTR has been successfully incorporated in the high field superconducting quantum interference device magnetometer setup developed in-house. It can also be incorporated in any low temperature physical property measurement system in which the temperature has to be varied in a controlled manner from 4.2 to 300 K and vice versa with uniform rates of heating and cooling.