Fast models for the evaluation of self-induced field effects in linear accelerators

Advanced applications of modern linear accelerators (linacs) strongly rely on the quality of the particle beams produced by such machines. Key examples of this kind include particle-driven radiation sources, plasma wakefield acceleration and lepton colliders for high energy physics. Such systems require use of high brightness electron beams implying the simultaneous coexistence of high peak currents, small transverse emittances and narrow energy spectra. The associated high phase space density results in strong self-induced electromagnetic fields, causing mutual interaction of the charged particles through space-charge and wakefield forces. These two sources of collective effects may be both present at significant levels, along with the strong applied fields, both longitudinal and transverse, found in high gradient linacs. As a result, beam dynamics studies capable of investigating the performance of a given device, as well as its operational limits, are crucial. However, the modeling of collective effects in simulation codes tracking large particle ensembles often requires significant, time-intensive numerical resources. In this paper we thus present alternative, simplified approaches for the description of space-charge and wakefield effects that permit streamlined computations. The features of such models are discussed, including their limitations and validating comparisons with existing tracking codes that utilize standard but more time-consuming approaches are shown. The beamlines we consider in our analyses are part of state-of-the-art facilities now under design for which new, challenging beam physics properties due to high fields and high beam brightness are expected. Thus, in addition to the introduction of new modeling techniques, our results provide an useful insight into advanced applications.