Conventional Synchrotron Beamline Optics

The X-ray beam from the source is monochromated, focused, and collimated to deliver a parallel beam of defined size and wavelength to the crystal. Because of the intrinsically superior optical qualities of synchrotron beams, the radiation delivered to the crystal is also superior to that from conventional sources. The crystal is mounted on a goniostat, which allows the crystal to be rotated. The crystal is usually flash-cooled to a temperature of 100 K by a cold stream of nitrogen gas to reduce radiation damage. X-rays are ionizing radiation and the free radicals produced as they pass through the protein destroy the crystal. Without flash cooling, protein crystals last only seconds on a synchrotron beamline. 

Beamlines. The greatest advantage of SR beamlines over conventional sources, when dealing with soft condensed matter research, is maybe not even the larger amoimt of photons which can be thrown onto the sample, but more so the fact that these photons are in less divergent beams. This means that optical elements can be used to condition the beam, which is not feasible with conventional sources. Obviously there are some drawbacks as well, but apart from the higher harmonic problem, which is discussed later, these mainly have consequences for the constmction of the beamline and should not concern users of these beamlines. However, it is a fact of synchrotron life that most experimenters using these facilities will one day encounter some problems due to technical failures connected... 

Figure 3.17 Measured far-IR intensity for the BESSY coherent synchrotron radiation (CSR) source, compared with mercury arc and Globar conventional thermal sources. In the picture the turn-on of the CSR source below 2cm is a real effect of the CSR emission process, while the drop off at the low frequency end is due to a combination of diffraction losses in the optical path of the beamline and to contributions of optical components in the interferometer. (Reprinted from ref. 102.)...

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