A Front End Design for the Advanced Photon Source

1. INTRODUCTION X-ray sources on next generation low emittance/high brilliance synchrotrons such as the 7-GeV Advanced Photon Source (APS) (1) have unique properties which directly affect the design of the front end of the beam line. The most striking of these are the large peak photon power densities expected for the insertion device (ID) x-ray sources. Undulators. for example. can have highly peaked photon power distributions with central densi ties approaching 300 kW/mrad~. Large power distributions can also be expected for some of the high critical energy wigglers. Front end components which intercept the photon beam produced by IDs must be able to absorb and safety dissipate the heat loads associated with their power distributions. In addi tion.detection of the position of the photon beam in some cases requires a precision in the range of a few microns. The information from such photon beam monitors is used primarily in the particle beam control loop in order to maintain the position and takeoff angle of the particle beam within some fraction of the beam size and angular divergence dictated by the emittance of the lattice. In most cases, these photon beam detectors must function in the high flux environment of the x-raY beam. The conceptual design of the front ends for the undulator. wiggler. and bending magnet (8M) sources on the APS take these unique characteristics into account. In addition. they perform four basic functions which are related to their role as the interface between the x-ray source on the storage ring and the downstream components on the experimental floor. These functions are: