This paper summarizes the low-loss design for the Spallation Neutron Source accumulator ring ["Spallation Neutron Source Design Manual" (unpublished)]. A hybrid lattice consisting of FODO arcs and doublet straights provides optimum matching and flexibility for injection and collimation. For this lattice, optimization focuses on six design goals: a space-charge tune shift low enough ( below 0.15) to avoid strong resonances, adequate transverse and momentum acceptance for efficient beam collimation, injection optimized for desired target beam shape and minimal halo development, compensation of magnet field errors, control of impedance and instability, and prevention against accidental system malfunction. With an expected collimation efficiency of more than 90%, the uncontrolled fractional beam loss is expected to be at the 10 24 level.

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MJVSTHCThe ASS has been brought into operation in October 1982 with multi-turn H" charge exchange injection. The Injection area of the AG3 hats been •edified to bring the H" beam from the 200 MeV linac through the main magnet fringe field to a stripping foil located within the magnet aperture. The injection syatea is described in detail and initial performance of the accelerator is reported.