10 GPa Control

J.-L. Laborier, C. Payre, N. Belkhier, P. Martin, E. Lelièvre-Berna
Institut Laue Langevin, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France

R. Bruyere, A. Prat
Institut Neel, CNRS, 25 Avenue des Martyrs, 38042 Grenoble Cedex 9, France

We present a fast and very precise control rack for continuously loaded pressure cells and presses. This rack can charge the device at up to 2 kbar of helium gas in 20 minutes, control ramps at 30 bar/min and maintain the pressure constant with variations around the set point of less than 0.2 bar. It is used with continuously load cells and VX-1 and VX-5 Paris-Edinburgh presses. Combined with the VX-5, it allows to regulate quickly and precisely the sample pressure up to 10 GPa at temperatures down to 3 K in our cryogen-free cryostat.

To simplify the use of the rack on the instruments, efforts have been made to ease its installation and pro- vide a very simple user interface. Once the power and compressed-air lines plugged, it only necessitates to connect the press or cell, switch it on and enter the set point. In case of power cut, overpressure or shutdown of the compressed-air line, the rack automatically stops and releases the pressure applied to the sample. This rack has been commissioned in 2010 and a second copy is under construction.

To achieve these performances, we use a 3 kbar compressor, two high-precision 2 kbar valves and a buffer. The innovative operating principle of the isolation valves is based on the elastic deformation of materials and is characterized by the absence of a stuffing box (0-ring). A Eurotherm controller maintains the gas in the buffer above the pressure required by the user and regulates the sample pressure by opening and closing the valves. One valve releases the pressure and the other injects the gas available in the buffer. For increasing (or decreasing) quickly the pressure in the press or cell, the controller disables the regulation loop and controls directly the compressor (or relief valve).