Collective Focusing of Intense Ion Beam Pulses for High Energy Density Physics Applications

The collective focusing concept in which a weak magnetic lens provides strong focusing of an intense ion beam pulse carrying an equal amount of neutralizing electron background is investigated by making use of advanced particle-in-cell (PIC) simulations and reduced analytical models. The original analysis by Robertson [Phys. Rev. Lett.\textbf{ 48}, 149 (1982)] is extended to the parameter regimes of particular importance for several high energy density physics applications. The present paper investigates: (a) the effects of a moderately strong magnetic field,\textit{ $\omega $}$_{ce}\ge $\textit{$\omega $}$_{pe}$; (b) suppression of the applied magnetic field due to the presence of the beam self-fields generated when $r_{b}\ge $\textit{c/$\omega $}$_{pe}$; and (c) the influence of a finite-radius conducting wall around the beam cross section. Here,$ r_{b}$ is the beam radius, $c$ is the speed of light, and\textit{ $\omega $}$_{ce}$ and\textit{ $\omega $}$_{pe}$ are the electron cyclotron and electron plasma frequencies, respectively.