A Bragg-Fresnel multilayer electron beam monitor for third generation storage rings

In anticipation of the small emittance of the third generation light source, BESSY II, we have developed a new approach to beam diagnostics based on the use of Bragg-Fresnel multilayer (BFM) optical components which will be able to withstand the high heat load expected. We report here on the successful performance of such a system as tested on a BESSY I dipole source. Because BESSY II will provide significantly smaller electron beam dimensions than BESSY I, the system was designed for operation at 6.53 nm (190 eV), well below the fiffraction limit of BESSY II. The optical system, designed with a reflecting lens and plane mirror, provides 1:0.8 image transfer with a spatial resolution of ∼ 7 μm. The source shape for different ring currents and operation modes of the storage ring has been measured and is represented here.