Thermal effects on optical performances of a prefocussing mirror for high-resolution soft-x-ray beamlines

Heating of grazing incidence mirror surfaces by absorbed soft X-rays from a synchrotron beamline has been studied numerically to evaluate resultant displacements of the thermally loaded surface. Subsequent ray-tracing analysis has provided the corresponding change in optical performances. This procedure has been applied in particular to a thermally loaded prefocussing ellipsoidal mirror to be used in a high-spectral-resolution soft-X-ray beamline in the U2 undulator beamline of ELETTRA, and ultrahigh brightness synchrotron radiation facility under construction in Trieste. Various cooling geometries have been investigated. A detailed analysis of the results indicates deterioration of imaging properties beyond the present fabrication tolerances only at extreme irradiation levels.