Piston-Cylinder Apparatus Operating at Liquid Helium Temperature

Abstract

Pressure experiments which demand truly hydrostatic conditions become very difficult in the range of temperatures below 77K and pressures up to 15 kbar. This is mostly due to the fact that all fluids become solid in this range, and therefore small nonhydro-static stresses cannot be completely avoided. Several techniques were developed for experiments in this range. Low temperature clamped cell technique uses a liquid pressure transmitting medium which is pressurized at room temperature and then cooled down to helium temperature (1) (2). The main disadvantages of this technique are: fairly high nonhydrostatic stresses which are generated during freezing of the pressure transmitting medium and the fact that the pressure can be changed only at room temperature. Much better results can be obtained by a similar technique which uses helium as the pressure transmitting medium. The pressure cell is pressurized with a helium gas compressor and then is cooled down to helium temperature (3). Nonhydrostatic stresses can be very nicely eliminated in this technique.