Annual Review 2024-2025

D I A M O N D L I G H T S O U R C E L I M I T E D 35 Additive manufacturing of X-ray mirrors for synchrotron beamlines Additive Manufacture (AM) in metals, colloquially known as 3D-printing, is increasingly used to create novel engineering components and light-weighted optics for astronomy and space applications. Compared to traditional “subtractive” techniques, such as drilling and cutting, AM can create intricate internal structures and fuse multiple components into a single piece. X-ray mirrors in silicon with slope errors < 100 nanoradians are becoming commercially available. However, “real world” performance on the beamline is limited by distortion under opto-mechanical clamping, localised heat- bumps induced by photon-beam illumination, and strain caused by differential expansion when dissimilar materials are cooled. To investigate if AM could solve such problems, a prototype X-ray mirror (Figure 2) was designed and fabricated together with the engineering group. The optical substrate, beamline mount and internal cooling pipework were combined into a single, monolithic piece. AM unlocks exotic internal cooling designs, including promoting turbulent flows, reduced coolant vibrations, and conformance to the X-ray heat-load distribution. The mirror was 3D-printed in an aluminium alloy over which the usual polishing processes were applied. Optical metrology demonstrates that surface quality is comparable to a traditional silicon mirror and is virtually immune to clamping deformations. Having demonstrated basic technology feasibility, the next step is determining how AM mirror technology can benefit Diamond-II beamlines. Cryo-cooled silicon crystal monochromator: measurement of flux versus power In-house designed cryo-cooled double crystal monochromators (DCMs) ensure delivery of highly stable X-ray beams. Temperature sensors confirm that indirect side cooling using liquid nitrogen via copper plates and indium foil interfaces is highly effective. The resilience of several existing crystal monochromators under higher power density beams on the Diamond-II machine was assessed using FEA and analytical models. A simple equation formulated earlier by the optics group scientists predicts critical power levels, above which the optics deformation increases steeply and diffraction efficiency decreases (Figure 3a). An experiment was carried out on several Diamond beamlines (I04, I07, I18 and I19) on a machine day to test the model: different amounts of power were deposited on the monochromator while the storage ring current was varied from 50 to 300 mA. At each ring current value, flux was measured in static and identical accelerator conditions on all beamlines. Excellent flux linearity was measured on all the beamlines under normal power operation conditions. On one beamline (I04) (Figure 3b) the power load was excessively increased by collecting the entire fan from the Front End custom aperture. Then, the flux levelled off, as predicted by our model (settings 1 & 3), because of the decreased efficiency of the DCM due to thermal distortions. The thermo-mechanical analytical deformation model in Figure 3a therefore is very effective and can be used to predict deformation caused by Diamond-II power quickly, making time-consuming FEA simulations unnecessary. O P T I C S A N D M E T R O L O G Y Figure 2: X-ray mirror produced by additive manufacturing.