Accumulator Ring Lattice for the National Spallation Neutron Source

The Accumulator Ring for the proposed National Spalla-tion Neutron Source (NSNS) [1] is to accept a 1:03 mil-lisecond beam pulse from a 1 GeV Proton Linac at a rep-etition 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 sys-tem, 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 accomodate 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 poten-tially dangerous betatron structure resonances are avoided. 1 THE LATTICE The lattice for the accumulator ring will consist of four su-perperiods, each containing a 90 arc and a long straight section [2]. The layout of the accumulator is shown in Figure 1. Each arc will consist of four identical FODO Figure 1: Accumulator ring layout. cells and will have a total betatron phase advance of 2 which will ensure zero dispersion in the long straight sec-tions. The arc half-cells will be 4 meters long and consis