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Design of a graphite filter/beryllium window for CHESS wiggler beamlines

We present a graphite-filter/beryllium-window design for the high power wiggler beam lines at CHESS. This design, which has been in operation since 1993 and proves to be very successful, employs a 0.25 mm thick highly-oriented pyrolytic graphite (HOPG) foil as a prefilter to reduce the heat load on the first vacuum beryllium window. Unlike most graphite filter designs in other synchrotron sources that rely entirely on radiative cooling, the HOPG filter in our design is brazed onto a water-cooled copper flange which substantially lowers its maximum temperature and prolongs its operational lifetime. We discuss the safety criteria that we have established based on theoretical calculations and infrared temperature measurements on the graphite filter and the beryllium window.