X-ray emission spectroscopy in a point-to-point focusing geometry using instruments that employ more than one analyzer crystal poses challenges with respect to mechanical design and performance. This work discusses various options for positioning the components and provides the formulas for calculating their relative placement. Ray-tracing calculations were used to determine the geometrical contributions to the energy broadening including the source volume as given by the beam footprint on the sample. The alignment of the instrument is described and examples are given for the performance.

We describe the design and show first results of a large solid angle x-ray emission spectrometer that is optimised for energies between 5.5 keV and 1.5 keV. The spectrometer is based on an array of eleven cylindrically bent Johansson crystal analysers arranged in a point-to-point Rowland circle geometry. The smallest achievable energy bandwidth is smaller than the core hole lifetime broadening of the absorption edges in this energy range. Energy scanning is achieved using an innovative design, maintaining the Rowland circle conditions for all crystals with only four motor motions. The entire spectrometer is encased in a high-vacuum chamber that allows fitting a liquid helium cryostat and provides sufficient space for in situ cells and operando catalysis reactors.

An instrument for X-ray emission spectroscopy (XES) based on perfect crystal Bragg optics was recently commissioned at beam line ID26 of the ESRF (European Synchrotron Radiation Facility). The spectrometer is used to record high-energy resolution fluorescence-detected X-ray absorption spectra with sublifetime resolution and to perform resonant and non-resonant XES. The hard Xray probe is material bulk sensitive and allows demanding sample environments (in situ chemistry, high pressure, etc.). Spectrometers for XES are being installed or designed at almost all upcoming synchrotron radiation sources worldwide. The particularity of the ID26 spectrometer is to accommodate five analyser crystals with exact Rowland tracking in the vertical plane and with crystals radii between 0.5 and 2 m.The main upgrade of the new version of this large instrument (3 tonnes, overall size 2.5 m and height 3 m) is to allow the change of the scattering angle over the range 0-180°. This involves rotating the entire spectrometer around a vertical axis that passes through the sample. In order to optimize the vibration stability of the spectrometer's structure, we chose to support the structure in multiple points and not only on three (kinematic mount) like it is specified to do with air pads. According to this choice, we have developed special foot holders for air pads.The calculations during the design phase have shown that we can obtain a first modal frequency of the spectrometer's structure at more than 30 Hz. To confirm our predictive calculations, we have performed some vibration measurements. Presentation of the ID26 emission spectrometer IIThe main challenge of this spectrometer is to be able to maintain low errors of positioning between the three key entities: the sample, the analysers crystals and †

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The root locus method of the treatment of stability problems in the field of servomechanisms is briefly summarised. A simple mechanical instrument of the analogue type (a summing device) containing no gear mechanisms, and designed to do most of the numerical work of the root locus method, is also described. f <