An approach for the optical and mechanical design of an X-ray beamline: application to the plane-wave CDI station CATERETÊ/SIRIUS

Abstract

Experiments involving nano-focusing or coherence applications require positional stability of a few nanometers and angular stability of tens of nanoradians for all critical optical components along the beamline (in the range of 1 Hz up to 2.5 kHz). Several optical components based on high-precision mechatronics principles with optimized dynamics to cope with those stability requirements have been recently designed and developed at LNLS. An approach combining optical and mechanical design methodologies and processes was applied to new beamline projects. The process starts with optical design using ray-tracing and wave propagation simulations aiming for the specified beam parameters. In a second step, alignment tolerances and stability issues are addressed in the mechanical design of each component. If those requirements cannot be reached in the predictive models based on the available technologies, size and shape of the optics itself or the optical scheme may be redefined restarting the optical simulation. This work applies this beamline design process to the CATERETÊ beamline, which allows for plane-wave CDI experiments. Using side-bounce deflecting cylindrical mirrors and a four-crystal monochromator, a focused beam size of ~ 40 x 30 μm2 (at 9 keV) with a depth-of-focus of 12 m (plane-wave) and high degree of coherence is obtained. We review key aspects of the optical and mechanical designs. In addition, we further extend the modelling process to enable systematic commissioning support by simulating beam parameters on diagnostic elements located downstream each optical element.