Optical Design and Initial Commissioning of the High-Pressure Beamline ID31 at the High Energy Photon Source

Abstract

Synchrotron X-ray diffraction under extreme pressure requires X-ray beams with high positional stability, high photon flux, and beam sizes and photon energies matched to a wide range of experimental conditions. To meet these requirements, a stability-oriented multi-scale X-ray focusing system has been developed for the ID31 high-pressure beamline at the High Energy Photon Source (HEPS). The optical system combines a liquid-nitrogen-cooled pseudo-channel-cut monochromator, compound refractive lenses (CRLs), and Kirkpatrick–Baez (KB) mirrors to provide beam sizes ranging from several tens of micrometers to below 200 nm over a photon-energy range of 20–75 keV. The routine micro-beam mode employs a pre-focusing two-stage CRL scheme, in which an upstream CRL group reduces the beam divergence before final focusing by a downstream CRL group, thereby increasing the photon flux delivered to the sample while maintaining flexible imaging conditions. Complementary single-stage CRL modes extend the operating range to quasi-submicrometer focusing and high-energy diffraction, whereas a KB mirror system provides submicrometer focusing for the SubμT platform. Initial commissioning at 30 keV achieved a beam size of 2.2 μm × 1.8 μm with a photon flux of 1.2 × 1013 phs/s for the routine GPT mode and 144 nm × 149 nm with a photon flux of 9.1 × 1011 phs/s for the KB focusing system. These results demonstrate the initial performance of the proposed optical design and establish ID31 as a versatile experimental platform for synchrotron X-ray diffraction and scattering under extreme conditions.