High Pressure Helium Gas Technique for Low Temperature Applications

A high pressure helium gas apparatus for low temperature applications is described. The gas apparatus consists of a high pressure generator, an experimental cell and a cryostat. The high pressure cell is connected to the generator with stainless tubings of 1.6 or 3.1 mm outer diameters, so heat transfer into the cryostat is low enough. A calibrated manganin gauge, situated in a separate temperature stabilized cell, is used to measure pressure with accuracy about 0.01 GPa while helium was still in the fluid phase. Upon crystallization of helium, pressure is calculated on the basis of the measured helium-crystallization temperatures and data on EOS of helium. The apparatus can be used to create high helium pressure up to 1.5 GPa and temperature less than 2K and to carry out electrical, magnetic and thermodynamic measurements. The technique is illustrated by the results of measurements of AC magnetic susceptibility of a single crystal of MnSi along the ferromagnetic phase-transition line up to a pressure of 1.2 GPa created by compressed helium.