AN ULTRASMALL ANGLE SCATTERING INSTRUMENT FOR THE DORIS-III BYPASS

The layout of the optics for a new small angle x-ray scattering instrument at the DORIS-III wiggler beamline BW4 was investigated by means of ray tracing and finite element calculations. The absolute intensity distributions at different locations of the beamline, especially in the focal plane, have been computed. The first crystal of a double crystal monochromator is the optical element that is most strongly influenced by thermal load. Thus, the distortion of this crystal surface due to thermal load was taken into account as well as the intended cooling system. The results show that the photon flux density at the focus is decreased by a factor of 0.2 due to this distortion.