Beam Dynamics of Non-Equipartitioned Beams in the Case of the SPL Project at CERN

The SPL [1] working group at CERN is studying a 2.2 GeV H- linac, which recuperates a large amount of RF hardware from the now decommissioned LEP at CERN. During the ongoing design effort for an optimized layout, it was found that in some cases non-equipartitioned beams tend to exchange energy between the longitudinal and the transverse planes. Strict energy equipartition, however, imposes tight restrictions on such a high energy linac and often contradicts the goal of cost effective design. On the other hand, stability charts derived from 2D Vlasov analysis suggest the existence of stable non-equipartitioned equilibria in certain regions of parameter space. Due to the low bunch current (22 mA) in the SPL, these regions are large enough to ensure stable machine operation for non-equipartitioned beams. Systematic multiparticle simulations with IMPACT [2] are used to apply the stability charts to the beam dynamics design of a realistic high energy linac. Using the example of the SPL, it is shown that designs with stable non-equipartitioned bunches are feasible, and how these designs react to mismatched input beams.