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Extremely high pressures over a million of atmospheres are required to deform diamonds permanently. Under dynamic high-pressure conditions, even such strong materials lose their strengths so rapidly that the initially pristine lattice transforms into complex dynamics. Here, we report femtosecond x-ray diffraction observations that directly resolve how shock waves deform the crystal lattice in the isotropic nano-polycrystalline form of diamond. The results show that the nano-grain reinforced diamond retains its strength at shock pressures far beyond its elastic limit until it finally approaches zero at 707 GPa, indicating the existence of brittle-ductile transition of nano-polycrystalline diamond under high-strain rate shock compression. The atomic-level deformation process of the diamond observed in this study is a key benchmark for designing high strength materials and simulating their behavior under extreme conditions.

The propagation of a shock wave in solids can stress them to ultra-high pressures of millions of atmospheres. Understanding the behavior of matter at these extreme pressures is essential to describe a wide range of physical phenomena, including the formation of planets, young stars and cores of super-Earths, as well as the behavior of advanced ceramic materials subjected to such stresses. Under megabar (Mbar) pressure, even a solid with high strength exhibits plastic properties, causing the shock wave to split in two. This phenomenon is described by theoretical models, but without direct experimental measurements to confirm them, their validity is still in doubt. Here, we present the results of an experiment in which the evolution of the coupled elastic-plastic wave structure in diamond was directly observed and studied with submicron spatial resolution, using the unique capabilities of the X-ray free-electron laser. The direct measurements allowed, for the first time, the fitting and validation of a strength model for diamond in the range of several Mbar by performing continuum mechanics simulations in 2D geometry. The presented experimental approach to the study of shock waves in solids opens up new possibilities for the direct verification and construction of the equations of state of matter in the ultra-high pressure range, which are relevant for the solution of a variety of problems in high energy density physics., Comment: 14 pages, 15 figures, submitted to Nature

We present results from the SPring-8 Angstrom Compact free electron LAser (SACLA) XFEL facility, using a high intensity ($\sim\!10^{20}\,$W/cm$^2$) X-ray pump X-ray probe scheme to observe changes in the ionic structure of silicon induced by X-ray heating of the electrons. By avoiding Laue spots in the scattering signal from a single crystalline sample, we observe a rapid rise in diffuse scattering, which we attribute to a loss of lattice order and a transition to a liquid state within 100 fs of irradiation, a timescale which agrees well with first principles simulations, but is faster than that predicted by purely inertial behavior. This method is capable of observing liquid scattering without masking or filtering of signal from the ambient solid, allowing the liquid structure to be measured throughout and beyond the phase change., Comment: 6 pages, 5 figures. Updated title and abstract

The Electron String type of Ion Sources (ESIS) was developed, constructed and tested first in the Joint Institute for Nuclear Research. These ion sources can be the appropriate sources for production of pulsed C4+ and C6+ ion beams which can be used for cancer therapy accelerators. In fact the test ESIS Krion-6T already now at the solenoid magnetic field only 4.6 T provides more than 10^10 C4+ ions per pulse and about 5*10^9 C6+ ions per pulse. Such ion sources could be suitable for application at synchrotrons. It was also found, that Krion-6T can provide more than 10^11 C6+ ions per second at 100 Hz repetition rate, and the repetition rate can be increased at the same or larger ion output per second. This makes ESIS applicable at cyclotrons as well. As for production of 11C radioactive ion beams ESIS can be the most economic kind of ion source. To proof that the special cryogenic cell for pulse injection of gaseous species into electron string was successfully tested using the ESIS Krion-2M., Comment: 9 pages