Sns Injection Simulations with Space Charge

The SNS accumulator ring will have a high intensity (~ 10) low energy (1 GeV) beam and required uncontrolled particle loss rates of ~ one part in 10. For these beam parameters, space charge effects could drive beam halo growth, which would lead to violation of the stringent loss criterion. In this paper we investigate the transverse halo growth due to space charge using a newly developed simulation tool, ORBIT [1]. We examine a variety of injection schemes, the effect of the lattice tune, and also the impact of using a FODO or doublet lattice. Painting schemes are examined for (1) directly correlated horizontal (X) vertical (Y) closed orbit bumps, (2) anti-correlated horizontal vertical bumps, and (3) horizontal closed orbit bump (fixed vertical smoke ring). Next we examine a wide range of lattice tunes for a fixed injection scheme. The tune is found to have a strong impact on halo growth. Finally we compare halo growth in FODO and doublet lattices with the same tunes and the same injection scenario. Neither lattice type is consistently superior regarding halo production. The space charge model in ORBIT uses a PIC calculation with an FFT method to calculate the force [2]. For cases shown here we use 480 transverse spacecharge kicks/turn (or about 60 per betatron oscillation), 50,000 macro-particles, and a 64x64 PIC grid. We inject particles with emittance < 120 p-mm-mrad, and we define halo as particles with emittance > 180 p-mmmrad, the acceptance of the SNS primary collimators. All cases are for injection of 2x10 particles. These results do not include lattice errors or wall impedance effects.