THE PERFORMANCE OF THE VACUUM-SYSTEM OF THE 800 MEV PROTON SYNCHROTRON, ISIS

The neutron source, ISIS, is the world's leading pulsed neutron facili ty, primarily used for condensed matter research using slow neutron sc attering techniques. The source is based on the bombardment of a urani um 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 r educe 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. Met al gaskets are used in all de-mountable joints. The system is pumped w ith triode sputter ion pumps and roughed by a carbon vane, dry combina tion claw and roots, and turbomolecular pumps. The entire system is fr ee from hydrocarbons. The performance of the system is reported includ ing an analysis of breakdown. Since operation began in 1984 there have been few failures apart from those caused by beam heating in the extr acted 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 mainte nance free.