An ultra-high vacuum, non-magnetic kappa geometry diffractometer has been designed and commissioned for the resonant soft x-ray scattering (RSXS) branch of the X-ray Science Division (XSD) Intermediate Energy X-ray (IEX) beamline 29-ID at the Advanced Photon Source (APS). Beamline 29-ID is managed by the XSD Magnetic Materials Group; the APS is an Office of Science user facility at Argonne National Laboratory. There were three main design goals for this diffractometer: kappa geometry, non-magnetic, and high-precision. The kappa geometry was chosen to allow for a large q-range and space for a sample environment (electric or magnetic fields). Non-magnetic components were used for all the components above and including the κ-arm to avoid disturbing magnetic or electric fields during experiments. Lastly, the diffractometer precision requirement of a sphere of confusion (SOC) of less than 50 µm was a key driving factor for this instrument in terms of rotation stages and machining precision.
The complete diffractometer can be seen in Fig. 1(a), shown installed into the RSXS UHV vacuum chamber at 29-ID. The precise SOC (< 50 µm) requirement drove the design method. In order to reach this goal, it was decided that a combination of precision machining, Finite element analysis, and stage precision would be used instead of calibrating an error-correction table. This has the advantage that the upper bound of the SOC requirement can be achieved without any control hardware, making the device more robust.
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Image: Fig1. (a) Image of the commissioned kappa diffractometer inside the RSXS vacuum chamber on the APS 29-ID beamline with the main components identified. (b) A close up model of the components above the f axis. The model also shows the new thermal break and thermal strap.