Calculation of wiggler spectrum and its absorption in media

The thermal and structural analyses of beamline and optical components exposed to high heat loads from insertion devices at the third generation synchrotron radiation facilities often require accurate determinations of the absorbed power profile. We have extended the existing PHOTON program (which calculates bending magnet spectra and their absorption in media) to the wiggler regime by taking into account the softening of the energy spectrum as the beam is observed off-axis in the horizontal direction. We describe a model for the wiggler power density and the total power in terms of commonly used parameters. Primarily using Wiggler B at the Advanced Photon Source (APS) as the model source, we find an absorbed power profile in a beryllium window that is markedly different from the power profile of the wigglere source itself: the absorbed power density increases rather than decreases in the horizontal direction. This finding may have a significant impact on the design of windows and other beamline components exposed to high heat load from insertion devices. (orig.)