An indirect pressure measurement method for the diamond anvil cell is described. Strain gauges measuring the force applied to the anvils, are calibrated against the actual pressure in the sample, measured by the ruby fluorescence technique. Diamond anvil cells (DAC) associated with laser heating are of particular interest in geophysical studies, since they can reproduce pressure and temperature conditions of the earth mantle. The classical determination of the pressure in a DAC consists in

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... ring the wavelength shift of ruby fluorescence lines under pressure. This shift has been calibrated by X-rays methods up to 1 MBar [1], Unfortunatley the ruby fluorescence method may sometimes be inconvenient since the ruby chips may take part in mineral reactions at high temperature, as it was shown by Madon [21 : a sample of synthetic (Mg 0 . 5 Fe 0 . 5)2 si0 4 ollv1ne P°w (t er was compressed with small ruby chips in a diamond cell to 240 kbar and laser heated to 130CPC. Examination of the recovered sample by transmission electron microscopy revealed the presence of = 30 % vol. of an aluminous ferro-maqnesian garnet produced by the reaction between olivine and ruby. Such reactions are clearly inconvenient for the study of phase transformations. There is therefore a need for a method of pressure determiantion that does not interfere with the reaction under investigation. We have developed an indirect method for measuring pressure, usinq strain gauges. Calibration procedure and results Fig. 1 -Strain gauges Bridge G : gauges, L, levers, C : cylinder, S : screw, E : extensometer, R : recorder. The DAC we use is of the type described by Mao and Bell [33. The anvils are 0.3 carat brilliant-cut diamonds with 16 facets and a flat table 0,5mm in diameter. Two strain gauges in series, glued on the load transmitting members ( fig. 1 ) measure their mean elastic deformation, a linear function of the load applied by the screw. Two other strain gauges, glued on the body of the cell, equilibrate the temperature Résumé -On décrit une méthode de mesure indirecte de la pression en cellule diamant. Des jauges de contrainte mesurent la force appliquée aux enclumes qui a été étalonnée en fonction de la pression dans l'échantillon par la méthode de fluorescence du rubis. Article published online by EDP Sciences and available at http://dx.