Vacuum chambers in composite material

Abstract

Vacuum chambers and windows required for colliding beam experiments in elementary particle physics research should be as transparent as possible for the secondary particles produced in the collisions. Until now, very thin wall chambers were made of stainless steel, aluminum alloys, titanium, or beryllium. Beryllium was the best for transparency but by far the most expensive. To provide an alternative method with good transparency at low cost, CERN has developed a new generation of chambers, made of composite materials and intended primarily for the proton–antiproton mode of operation of the Super Proton Synchrotron. These chambers consist of very thin metallic pipes for vacuum, reinforced by a carbon fiber structure for mechanical stability and clad with a second metallic layer to give electromagnetic screening. Chamber elements have been made by industry and tested extensively at CERN. These elements are up to 1.8 m in length with circular cross-section diameters of 50 to 150 mm and have 0.5–1.5 mm thick walls of carbon fiber/epoxy composite. The combined metallic layers have only 70–120 μm total thickness which is sufficient to meet the requirements regarding gas desorption in ultrahigh vacuum and electromagnetic shielding of the collider detector arrays from the circulating bunched beam. The chambers are bakable up to 130 °C, have a global leak rate over a typical 10-m section of less than 1×10−10 mbar l/s and an outgassing rate of about 10−12 mbar l/s cm2. They are almost as transparent as Be chambers but cost only about 15% as much. A set of carbon fiber vacuum chambers was glued together to a total length of 13 m and successfully tested.