XRD1 Beamline Description

Overview

The X-Ray Diffraction 1 (XRD1) beamline exploits a powerful wiggler as source of radiation. The photon beam produced is focussed to the sample in the experimental hutch using a toroidal mirror.  A cylindrical mirror is used to collimate the beam before the monochromator, in order to maximize the energy resolution to few electronvolts.  The resulting flux at the sample is the range 10¹²-10¹³ photons/second, with a natural footprint of  700 um (H) x 200 um (V). The available energy range at the experiment spans from 4 to 21.5 keV. The beamline has been designed – in collaboration with the Istituto di Cristallografia, CNR -- to perform a wide variety of measurements and experiments, all based on diffraction..

Insertion Device

The W140 permanent multipole wiggler is a 59 poles with a period of 140 mm. The insertion device is divided in three sections and the total magnetic length is 4130 mm with an optical length of 4500 mm. The magnetic field B is 1.6 T at 22 mm gap with a deflection parameter K y of 20.92.
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

XRD1 has the traditional layout used in case of important horizontal X-ray beam divergence,with a Collimator Cylindrical Mirror (CCM) faced up, a Double Crystal Monochromator (DCM) dispersing in the vertical plane and a bendable Focusing Toroidal Mirror (FTM) faced up. The horizontal acceptance is 1.5 mrad limited by the FTM sagittal radius and the vertical acceptance is 0.18 mrad.Also in this case the vertical acceptance is limited by the lengths of both the mirrors due to the grazing angle of 3.0 mrad.
A mask determines the angular acceptance and stops low-energy radiation from the wiggler. After about 22 m from the source the beam is collimated in the vertical direction by means of a platinum coated cylindrical mirror with a radius of curvature of 14.8 km. At 24 m from the source, a Si 111 double crystal monochromator permits to select a specific energy. At 28 m from the source, a bendable toroidal 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 a downstream 4-quadrant beam position monitor keeps the vertical position of the beam fixed in space.