Dynamic Space Charge Calculations for High Intensity

Space-charge-induced emittance growth and halo generation could lead to unacceptably high beam loss in high intensity rings, such as the SNS [1]. In such accelerators, uncontrolled losses to the walls as small as one part in 10 would lead to activation, making maintenance difficult. For this reason it is essential to understand the effects of space charge on beam dynamics, and halo generation in particular, in high intensity rings. We have undertaken the study of space charge dynamics in high intensity rings using a particle tracking approach, with self-consistent evaluation of the space charge forces through a particle-in-cell model. Because of the stringent loss requirements, it is necessary to thoroughly guarantee the reliability of these calculations to high precision through comparison with experiments and through convergence studies. In this paper we present the results of convergence studies in the parameters of the model, namely, the number of macroparticles, the resolution in the adopted FFT algorithm, the smoothing parameter, and the time step size. Although present calculations have been extended to more than 10 macroparticles on individual UNIX workstations, it will be necessary to increase another one to two orders of magnitude to obtain the necessary precision. To accomplish this, we have constructed and are now using a LINUX parallel computer from low cost components.