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XRD1 Beamline Description

Overview

The X-Ray Diffraction 1 (XRD1) beamline has been designed (in collaboration with the Istituto di Cristallografia - CNR) primarily for macromolecular crystallography, but the characteristics of the beamline permit to perform a wide variety of experiments: the beamline hosts small molecules, protein crystallography, powder diffraction, high pressure physics and solid-state experiments.


Insertion Device

The insertion device of the XRD1 beamline is shared and used simultaneously with the SAXS beamline. The insertion device is a hybrid multipole wiggler, composed of three sections for a total length of 4.5 m, with a fixed working gap of 22 mm and B=1.6T. The white beam resulting from the source is cut to 4 keV with a series of cooled graphite layers and is then monochromatized.

Beamline Layout



A mask determines the angular acceptance and stops unwanted radiation from the wiggler. After about 22.3 m from the source the beam is collimated in the vertical direction by means of a Pt coated cylindrical mirror with a radius of curvature of 14.8 km. At 24.5 m from the source, a Si 111 double crystal monochromator permits to select a specific energy. At 28.0 m from the source, a bendable toridal mirror, with 55 mm and 9.3 km of sagittal and tangential radius, permits to focalize the monochromatic beam with dimensions at the sample of 0.7 x 0.2 mm. Acting on the focusing mirror tilt, a rapid feedback loop using downstream 4-quadrant ionization chamber mantains the vertical position of the beam fixed.


 


Monochromator

A Si(111) double-crystal fixed-exit monochromator, in the parallel nondispersive mode, is used to select a specific energy in the range of between 4 and 21 keV, with a resolution of 2 eV. Due to the improvements in the ring (top-up mode), an upgrade of the direct water cooling was necessary in order to reduce the thermal expansion, and, since 2015, the two crystals are cryogenically cooled by means of a LN2 closed loop system (Bruker). Parallelism of the surfaces of the two crystals is guarateed by a piezo stage acting on the second crystal: a rapid feedback loop using downstream 4-quadrant ionization chamber mantains the flux intensity at the maximum. The monochromator is routinely calibrated evaluating the absorption edge from fluorescence signal of reference materials (usually Se edge) and the diffraction from NIST standards (usually LaB6).


Last Updated on Friday, 08 January 2016 16:56