Pushing a pressure standard: A challenge for understanding systems at extreme conditions is knowing the exact pressure at which exotic behaviors occur. This situation is caused by the lack of an absolute pressure-density relationship of standard pressure calibrants. Fratanduono et al. conducted a series of dynamic compression observations on platinum and gold to establish a high-pressure scale for these metals up to terapascal conditions (see the Perpsective by Jeanloz). This work provides a robust calibration when using these standards in high-pressure devices such as diamond anvil cells. Science , abh0364, this issue p. 1063 ; see also abi8015, p. 1037

We report measurements of the compressibility of ramp compressed tantalum to a final stress of 2.3 TPa corresponding to threefold volumetric compression. Using these data, we extended the experimental constraint on the Ta cold compression curve by an order of magnitude in pressure. By combining the resulting data with previous measurements of shock compression and ambient pressure heating, we construct an experimentally bounded and thermodynamically consistent equation of state model for Ta which has 2% uncertainty in pressure at 1 TPa. We therefore propose Ta as an in situ pressure scale for laser-heated static compression experiments which were recently able to reach terapascal pressures and thousands of degrees Kelvin. Our new equation of state of Ta is experimentally constrained at extreme pressures and temperatures relevant to a wide range of planetary interiors and will allow for more accurate comparison between experimental measurements and theory at extreme conditions.

An experimental platform for dynamic diamond anvil cell (dDAC) research has been developed at the High Energy Density (HED) Instrument at the European X-ray Free Electron Laser (European XFEL). Advantage was taken of the high repetition rate of the European XFEL (up to 4.5 MHz) to collect pulse-resolved MHz X-ray diffraction data from samples as they are dynamically compressed at intermediate strain rates (≤10³ s⁻¹), where up to 352 diffraction images can be collected from a single pulse train. The set-up employs piezo-driven dDACs capable of compressing samples in ≥340 µs, compatible with the maximum length of the pulse train (550 µs). Results from rapid compression experiments on a wide range of sample systems with different X-ray scattering powers are presented. A maximum compression rate of 87 TPa s⁻¹ was observed during the fast compression of Au, while a strain rate of ∼1100 s⁻¹ was achieved during the rapid compression of N₂ at 23 TPa s⁻¹.