All‐aluminum‐alloy ultrahigh vacuum system for a large‐scale electron–positron collider

An all‐aluminum‐alloy vacuum system for the TRISTAN ring (30 GeV) is now under construction. Ordinary stainless steel components and stainless steel–aluminum transitions have been eliminated as much as possible from the TRISTAN design. Suitable aluminum‐alloy vacuum chambers, elliptical bellows, fittings, flange/gasket/bolt, nut and washer combinations, feedthroughs, gauges, optical windows, sputter ion pumps, turbomolecular pumps, all‐metal valves, and related aluminum‐alloy vacuum components have been developed. The beam chambers of the dipole and quadrupole magnets, all‐metal gate valves, ceramic chambers, and the seamless bellows are directly joined by a fully automatic welding machine, i.e., without using flanges. For demountable joints, a new Conflat‐type seal, which consists of Cr2N‐coated superalloy flanges, is used. The outgassing rate after baking 24 h at 150 °C is several times 10^-14 Torr 1/s cm² for specially extruded beam ducts. The sputter ion pump, which is made of aluminum alloy, has an extremely short pumpdown time to ultrahigh vacuum, on the order of 10^-9 Torr after only 24 h of initial operation, and on the order of 10^-10 Torr after a 150 °C, 24 h, initial bakeout procedure.