Accumulator Ring lattice for the National Spallation Neutron Source

The Accumulator Ring for the proposed National Spallation Neutron Source (NSNS) is to accept a 1.03 millisecond beam pulse from a 1 GeV proton linac at a repetition rate of 60 Hz. For each beam pulse, 10¹⁴ protons are to be accumulated via charge-exchange injection. A 295 nanosecond gap in the beam, maintained by an RF system, will allow for extraction to an external target for the production of neutrons by spallation. This paper describes the four-fold symmetric lattice that has been chosen for the ring. The lattice contains four long dispersion-free straight sections to accommodate injection, extraction, RF cavities, and beam scraping respectively. The four-fold symmetry allows for easy adjustment of the tunes and flexibility in the placement of correction elements, and ensures that potentially dangerous betatron structure resonances are avoided