Speaker
Description
The newly constructed Debye beamline at the Swiss Light Source (SLS), available for users after the SLS upgrade mid-2025, is aiming at X-ray absorption spectroscopy and X-ray diffraction analysis to probe the chemical and electronic structure of functional materials under operating conditions. As part of the optical system, a new quick scanning channel-cut monochromator with its control system was developed, providing quasi-simultaneous X-ray absorption spectroscopy (XAS) and X-ray diffraction analysis (XRD). The monochromator is equipped with liquid nitrogen cooled Si(111) and Si(311) channel-cut crystals giving an operational energy range of 4.5 keV to 60 keV. A cutting-edge motion control system provides a diverse range of control options, facilitating Quick-scanning Extended X-ray Absorption Fine Structure (QEXAFS) through sinusoidal motion and custom trajectories as well as precise step-scanning measurements, all seamlessly executed with the same direct-drive motor.
The Bragg axis is controlled by a direct-drive servo motor installed on the atmospheric side of the vacuum chamber and the motion is transferred into the vacuum chamber by a standard ferrofluidic-sealed rotary feedthrough. A rotary encoder mounted next to the crystal stage provides angular feedback to the control loop giving accurately the crystal orientation with a resolution of 0.13 µrad (Figure 1). The control system was evaluated to provide the best available angular accuracy resulting in a stand still position error of ± 1 encoder step after a settling time of well below one second, without the need of physical brakes or goniometers. To realize QEXAFS mode, precise motion with top speeds of up to 100 deg/s or 50 milliseconds per spectrum can be achieved.
A significant improvement on today’s monochromators is the software of the motion controller, resulting in complex motion sequences that are easy to program for the user (Figure 2). A standard set of controls are available, from manual control of the Bragg angle to sinusoidal oscillation for combined XAS/XRD measurements or step-scanning. An additional operational mode has been implemented to program customizable trajectories allowing for variable speeds during an XAS scan, thereby enhancing the data quality in the EXAFS region through progressively slowing the motion, envisioned to provide significant improvement for fluorescence detected XAS collected with continuous motion. To simplify the data acquisition and processing pipeline, precise position triggered signals are emitted from the motion controller for accurately delimiting the individual QEXAFS scans and triggering the XRD detector as well as real time data reduction of QEXAFS scans.
| I plan to submit also conference proceedings | Yes |
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