A beryllium window for electron beam injection and extraction in an aluminium alloy uhv system, TRISTAN

The window for electron beam injection and extraction in the accumulation ring of TRISTAN consists of an aluminium alloy frame and a vacuum tight beryllium foil. A beryllium foil is used because of low loss in electron beam energy, mechanical strength necessary to isolate vacuum and atmosphere, high thermal conductivity and low residual radioactivity. When an electron beam welding method is used to make a joint between a beryllium foil and an aluminium alloy there can be problems with the reliability during the heat cycling. A simplified electron beam welding method is described to make a beryllium window. Results of helium leak tests on the beryllium window during thermal cycling using an aluminium Helicoflex seal are given. (U.K.)