Figure 3
Plan of the elements that define the beam on the high-brilliance undulator beamline ID2, ESRF. The low beam divergence, coupled with the use of guard slits and beam defining slits from the source and spread over 23 m (27–50 m from the source, with the final guard slits as close as possible to the crystal, as discussed in the text, to minimize scatter). This results in an X-ray beam that is close to parallel. The improvement in the signal-to-noise ratio possible by the pushing back of the detector (as described in the text) is dependent on a long distance between the crystal and the effective source of X-rays. The effective source position will clearly be determined by the nature and positions of the optical elements. For ID2, the great distance between the toroidal mirror, the last optical element, and the crystal ensures that this aspect of the station design is not limiting. |