Conceptual Design of a Dedicated SAXS Beamline at NSRRC

Abstract

A dedicated small‐angle X‐ray scattering (SAXS) beamline using a new X‐ray source generated by an In‐Acromat superconducting wiggler (IASW6) insertion device is under construction at the National Synchrotron Radiation Research Center (NSRRC). The IASW6 with peak magnetic field of 3.1 T, magnet period of 6.1 cm, and total length of 96 cm, can provide a photon flux ∼ 1012 – 1013photons/s/0.1%bw in the energy range of 5 – 23 keV. Taking the central 0.2 mard horizontal radiation fan from the source with a beam divergence of 200 and 392 μrad in the vertical and horizontal directions, respectively, the dedicated SAXS beamline is oriented for nano to meso‐structural research in soft matter, including liquid crystals, macromolecular solutions, polymers, as well as in nanoparticles, ceramic, and alloys. The SAXS beamline adopts the design of the double‐monochromator used in the beamline SIYBLS at ALS, which integrates a Si(111) double crystal monochromator (DCM) and a Mo/B4C double multilayer monochromator (DMM) into one cradle for fast exchange between the two monochrmators. Equipped with a collimating mirror (CM) and a toroidal focusing mirror (FM) with 1:1 focusing ratio, this beamline provides two types of SAXS measurements: high‐Q resolution and high flux, by using either the DCM or DMM. The SAXS beamline also provides energy scan with an energy resolution from 1 to 10 eV for anomalous SAXS (ASAXS) measurements. A specially coated reflecting mirror is also installed after FM to provide a suitable photon beam for grazing incident SAXS of liquid surfaces. Ray tracing simulation results show that at 8 keV and with DCM, a high quality photon beam of beam size (0.5 mm) and beam divergence (± 50 μrad) with a flux of ∼ 1011 photons/s can be obtained for high‐Q resolution SAXS measurement. The photon flux can be increased by one order of magnitude when the DMM is used; however, the beam size and divergence are both slightly increased.