The performance of the vacuum system of the 800 MeV proton synchrotron, ISIS

Abstract

The neutron source, ISIS, is the world's leading pulsed neutron facility, primarily used for condensed matter research using slow neutron scattering techniques. The source is based on the bombardment of a uranium or tantalum target by an 800 MeV high intensity proton beam from a rapid cycling synchrotron. A brief description is given of the vacuum system of the synchrotron and beam line to the target. Key factors in the design of the system are reliability and minimum maintenance, to reduce exposure of operators to radiation. Ceramic vacuum chambers make up two thirds of the ring to reduce eddy current losses in the pulsed magnets: all other chambers are constructed from stainless steel. Metal gaskets are used in all de-mountable joints. The system is pumped with triode sputter ion pumps and roughed by a carbon vane, dry combination claw and roots, and turbomolecular pumps. The entire system is free from hydrocarbons. The performance of the system is reported including an analysis of breakdown. Since operation began in 1984 there have been few failures apart from those caused by beam heating in the extracted beam line, which has caused leaks in joints. As diagnostics and beam control have improved, these occurrences have become increasingly rare. This has resulted in a vacuum system virtually fault and maintenance free.