Position and flux stabilization of X-ray beams produced by double-crystal monochromators for EXAFS scans at the titaniumK-edge

Abstract

SynopsisDual loop active feedback stabilisation of the position and monochromatic flux of the beam at the output of the double crystal monochromator is described. The efficacy of the proposed stabilisation system is demonstrated in EXAFS spectroscopy measurements on inhomogeneous diluted Ti containing samples. AbstractWe report on the simultaneous and active feedback stabilisation of x-ray beam position and monochromatic beam flux during EXAFS scans at the Titanium K-edge as produced by a double crystal monochromator beam line. The feedback is generated using two independent feedback loops using separate beam flux and position measurements. The flux is stabilized using a fast extremum-searching algorithm that is insensitive to changes in the synchrotron ring current and energy dependent monochromator output. Corrections of beam height are made using an innovative transmissive beam position monitor instrument. We demonstrate the efficacy of the feedback stabilisation method by comparing the measurements of EXAFS spectra on inhomogeneous diluted Ti containing samples with and without feedback applied.

XAS and XES Techniques Shed Light on the Dark Side of Ziegler–Natta Catalysts: Active‐Site Generation

“…In particular,t oo vercome the experimental difficulties caused by beam drift and minute sample inhomogeneities intrinsic to XASexperiments on heterogeneous catalysts at these low X-ray energies, it was necessary to develop afeedback mechanism on the X-ray optics of BM26. [24] Moreover, because of the high photon flux adopted during vtc-XES measurements (more than 10 12 photons per second), the samples were found to suffer from radiation damage on af ast timescale ( % 10 s). To circumvent this problem,e ach point of the vtc-XES spectrum was collected on adifferent sample spot irradiated for 2seconds, and the intensity was normalized to the total fluorescence-yields signalr ecorded with as olid-state detector.T he micrometric size of the beam allowed us to have sufficient fresh points on the sample (1.3 cm diameter pellet) to collectafull vtc-XES spectrum.…”

“…[24] Moreover, because of the high photon flux adopted during vtc-XES measurements (more than 10 12 photons per second), the samples were found to suffer of radiation damage on a fast time scale (~ 10 s). To circumvent this problem, each point of the vtc-XES spectrum was collected on a different sample spot irradiated for 2 seconds, and the intensity was normalized to the total fluorescence yields signal recorded with a solid state detector.…”

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