Parallel Computation of Beam-beam Interactions including Longitudinal Motion

In beam-beam macroparticle simulations for collider rings, the accurate determination of the incoherent spectrum and potentially unstable coherent modes requires (1) large numbers of collisions, and (2) accurate electric field solutions at each collision. On a single processor, a selfconsistent simulation typically uses a 2D model of the beam-beam interaction in order to achieve a reasonable computation time, however for the long (∼0.3m) bunches in the LHC we wish to include the third dimension in order to account for effects such as longitudinal motion, crossing angle, and the beam size and density variations. We describe here a parallel algorithm, developed with MPI on a small commodity Linux cluster, to extend our simulation code BeamX from 2D to 3D using longitudinal subdivision (slicing) of the bunches. Although this paper concentrates on the computing methods, some performance trials and example results will also be shown.