There are two experimental techniques capable of generating the very high pressure and temperature conditions of the deep interior of planets: laser-heated diamond cells and shock compression. In laser-heated diamond cells temperatures of over 4000 K have been achieved at pressures up to 200 GPa (2 Mbar) (Boehler, 1993). The main advantage in using diamond cell over shock experiments is that P-T conditions can be kept constant for long periods of time (hours), and this allows a large variety of visual, spectroscopic and X-ray diffraction measurements. The principal drawback to the diamond cell are small sample size, temperature gradients, and in some cases chemical reaction of the sample with the diamond or the pressure medium. The installation of high-pressure beam lines at synchrotron facilities, along with recent developments in X-ray diffraction techniques, have significantly improved our ability to measure the phase behaviour of many materials at extreme pressure and temperature conditions.
In comparison to the wide range of temperatures and pressures accessible to the diamond cell method, shock experiments using guns or lasers provide measurements of densities and sound velocities only along a material-specific, nearly adiabatic P-T path (Hugoniot). Another drawback to the shock method is the short experimental time scale. However, the maximum pressures attainable by shock methods are virtually unlimited.
In this paper the experimental technique for obtaining reliable data at simultaneously high pressure and high temperature employing the laser-heated diamond cell is described. A schematic cross-section of a laser-heated diamond cell is shown in Figure.
The principal components of a diamond cell are two diamond anvils compressing a gasket.