High-pressure synchrotron radiation x-ray diffraction (XRD) is an essential method for studying in situ characterization of material properties under extreme conditions. The undulator beamline BL10XU at SPring-8 has been dedicated to powder XRD at high pressure in a diamond anvil cell using high-energy monochromatic micro-focused x-rays. High-pressure activities at BL10XU cover a wide range of scientific fields, including fundamental physics, high-pressure chemistry, materials science, and earth and planetary sciences. Recently, high spatial resolution x-ray probe for XRD is required since a high-pressure sample size is miniaturized with extending the pressure range and electrodes for resistance measurements. Structural analysis of non-crystalline materials at extremes of pressure and temperature is also a critical challenge in high-pressure synchrotron XRD. We have been developing the high-energy x-ray focusing optical system suitable for high-pressure XRD in BL10XU, for the purpose of determining the structural information and densities of polycrystalline and amorphous/liquid.
    The x-ray focusing is a key technique in high-pressure synchrotron radiation experiments. In the beamline BL10XU, high-energy x-ray beam is focused using x-ray compound refractive lenses (CRL). In order to realize a sub-micro sized beam, a two-stage x-ray focusing optical system was installed, comprising two kinds of CRLs and a pinhole as virtual source. We successfully generate a focused x-ray beam less than 1-µm at 30 keV. High-pressure XRD measurements using the sub-micro x-ray beam have started to extend the accessible pressure range in diamond anvil cells with particular anvil geometry such as the double stage configuration. The smaller x-ray probe can be also applied to resolve stress and temperature gradients, compositional heterogeneity, and texture, and could be useful for high-pressure multiple grain XRD. For high-energy x-ray range between 45 and 62 keV, the energy tunable refractive optical system has been designed and installed, which consists of 6 units containing Al parabolic lenses. So far, at 50- and 62-keV x-ray beam can be focused down to 10-µm and 20-µm, respectively, by the combination of Al-CRL and another CRL devices. This is expected to approach to the quantitative study of the structure of non-crystalline materials in a diamond anvil cell because XRD data with high momentum transfer Q provide sufficiently high resolution in real space. Here we present overview the current x-ray focusing optics and high-pressure studies at BL10XU.