Nonlinear δf simulation studies of intense ion beam propagation through an alternating-gradient quadrupole focusing field

Abstract

Newly-developed perturbative (δf) particle simulation techniques are used to investigate the detailed stability and transport properties of an intense ion beam propagating through an alternating-gradient focusing lattice with initial Kapchinskij-Vladimirskij (KV) distribution. Stability properties are investigated over a wide range of beam current and focusing field strength. In the unstable region, large-amplitude density perturbations with low azimuthal harmonic numbers, concentrated near the beam surface, are observed, and their nonlinear consequences are discussed. In the stable region, it is shown that the KV beam distribution propagates quiescently over large distances (up to 500 lattice periods in the simulations). The δf-scheme used in the present numerical studies exhibits minimal noise and accuracy problems in comparison with standard particle-in-cell simulations.