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Department Optics and Beamlines

BElChem

The BElChem facility consists of two beamlines with two endstations in two separate hutchs and an additional sample preparation/chemical lab. BElChem-PGM (plane grating monochromator) covers the soft X-ray energy range, whereas BElChem-DCM (a dipole magnet sourced beamline) with a double crystal monochromator (DCM) covers the tender X-ray energy range. For detailed information, see the technical report.

Our team took care of the design and construction of the new BElChem-PGM beamline, as well as the refurbishment of the motion controllers for the DCM beamline


PGM beamline

The source for the BElChem PGM beamline is a planar undulator with a period length of 49.4 mm (U49-2) and a minimum gap of 16 mm. The optical elements and layout of the beamline have been optimized to deliver a high photon flux over a broad energy range, in particular at energies above 800 eV, with moderate spectral resolution.  The beamline is composed of three mirrors with an included angle of 177°. The small incident angle of 1.5° ensures high reflectivity even at photon energies above 1000 eV. The entire photon energy range is covered by a single, optimized blazed grating with a line density of 600 l/mm. This makes the BElChem-PGM beamline very user-friendly since experiments can be conducted without the need to switch gratings and adapt beamline settings to different gratings. While the high efficiency of the 600 l/mm grating is the best choice for most applications, two additional gratings with 400 l/mm (optimized for low photon energies) and a 1200 l/mm grating (optimized for very high spectral resolution, not shown) are available for the users if needed. The X-rays are focused by a toroidal mirror M4 to the endstation. The spot size as obtained by ray tracing simulations is around 100 µm × 20 µm (horizontal × vertical) with a 20 µm exit slit for most photon energies and a fixed focus constant of cff = 2.25.


DCM Beamline

The source for the BElChem-DCM is the dipole bending magnet 4.2. T. The beamline is composed of two cylindrical mirrors (M1, M2) and a double crystal monochromator containing a Si(111) crystal pair. The M1 mirror will collimate the white beam onto the first crystal of the DCM. Horizontal focusing of the beam will be achieved by the second (bendable) crystal of the DCM. The M2 mirror will be used for vertical focusing of the beam and for directing it to the experimental position. The usable photon energy range will be approximately from 2.4 to 10 keV.  The downstream photon flux will remain above 1011 photons·s−1·0.3A−1/0.1%BW for photon energies up to 8 keV. The beamline resolution will range from about 0.2 eV at 2.4 keV to 1.3 eV at 10 keV. In addition, the simulations predict a beam dimension of about 400 (vertical) × 200 (horizontal) μm2, irrespective of the photon energy at the location of the experiment.

© 04/25 S.V.