Cylindrical mirrors with sagittal curvature are known for non-ideal focusing due to strong aberrations. However, the small emittance of undulator sources at new upcoming fourth-generation synchrotrons causes the footprint of the beam on a sagittal cylinder to be small enough to permit almost aberration-free focusing. The use of side deflecting sagittal cylinders in the optical design of synchrotron beamlines brings advantages to the beam performance: a) it improves stability, because horizontal plane is less a effected by ground vibrations, b) it keeps the beam height with respect to the floor, c) the beam is less sensitive to slope errors in the sagittal plane. Furthermore, a sagittal cylinder in combination with a meridional cylinder or ellipse allows the change of focal spot size and position. In this work, we present the optical scheme of three beamlines including sagittal cylinders for the fourth-generation synchrotron SIRIUS. In MANACA beamline (protein crystallography) a sagittal cylinder and a meridional ellipse face each other in the horizontal plane. By changing the incidence angle of both mirrors in the same direction beam size at sample can be changed from 10 to 100 μm. In SAGUI beamline (SAXS and XRD) both mirrors face the same direction. Changing the incidence angle in opposite direction enables to change the focus position by tens of meters. In CATERETE beamline (Coherent Diffraction Imaging) the two mirrors face each other to create a highly coherent plane wave with a focal spot of 40 μm. We compare the performance of each beamline with their ideal optics counterpart, using wave propagation simulations (SRW).
The soft X-ray beamline IPE is one of the first phase SIRIUS beamlines at the LNLS, Brazil. Divided into two branches, IPE is designed to perform ambient pressure X-ray photo-electron spectroscopy (AP-XPS) and high resolution resonant inelastic X-ray scattering (RIXS) for samples in operando/environmental conditions inside cells and liquid jets. The aim is to maximize the photon flux in the energy range 200-1400 eV generated by an elliptically polarizing undulator source (EPU) and focus it to a 1 μm vertical spot size at the RIXS station and 10 μm at the AP-XPS station. In order to achieve the required resolving power (40.000 at 930 eV) for RIXS both the dispersion properties of the plane grating monochromator (PGM) and the thermal deformation of the optical elements need special attention. The grating parameters were optimized with the REFLEC code to maximize the efficiency at the required resolution. Thermal deformation of the PGM plane mirror limits the possible range of cff parameters depending of the photon energy used. Hence, resolution of the PGM and thermal deformation effects define the boundary conditions of the optical concept and the simulations of the IPE beamline. We compare simulations performed by geometrical ray-tracing (SHADOW) and wave front propagation (SRW) and show that wave front diffraction effects (apertures, optical surface error profiles) has a small effect on the beam spot size and shape.
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