Developments and Applications for All-Aluminum Alloy Vacuum Systems

Aluminum and aluminum alloys have long been among the preferred materials for ultrahigh vacuum (UHV) systems operating in the 10−10–10−11 torr (10−8–10−11 Pa) range. Pure aluminum and aluminum alloys have an extremely low outgassing rate, are completely nonmagnetic, lack crystal structure transitions at low temperatures, are not sources of heavy metals contamination in semiconductor processing applications, have low residual radioactivity in radiation environments, and are lightweight. Because of aluminum's high thermal conductivity and low thermal emissivity, aluminum components can tolerate high heat fluxes in spite of the relatively low melting point of aluminum.Recently developed aluminum alloys and new surface finishing techniques allow the attainment of extremely high vacuums (XHV) in the 10−12–10−13 torr (10−10–10−11 Pa) range. XHV technology requires the use of special aluminum alloy flange/gasket/bolt, nut and washer combinations, aluminum alloy-ceramic seals, windows, bellows, right-angle and gate valves, turbomolecular pumps, sputter ion pumps and titanium sublimination pumps, Bayard-Alpert ion gauges, quadrupole mass filters, and related aluminum alloy vacuum components. New surface treatment methods and new techniques in welding and extremely sensitive helium leak testing are required. In short, a whole new technology has been developed to take advantage of the opportunities presented by these new vacuum materials. This article describes some of these newly developed fabrication technologies and vacuum materials.The TRISTAN electron-positron collider constructed at the National Laboratory for High Energy Physics in Japan is the first all-aluminum alloy accelerator, and the first to use UHV technology.