Equilibria for intense ion beam transport in low-pressure gas or vacuum

Two fluid equilibrium solutions for intense ion beam transport in low-press ure gas or vacuum are derived. The equilibria that are most relevant to bea m transport have neutralizing electrons drifting in the same direction as t he beam. These solutions require a small net positive charge within the bea m channel to support an equilibrium radial electric field to allow the elec trons to ExB drift axially. At the extremes of the domain of allowable solu tions this electric field approaches zero and complete charge neutrality is achieved. In this case, two solutions are obtained. The first describes ba llistic beam transport with complete neutralization of the beam current by the electrons, and the second describes pinched beam transport with no neut ralizing electron current. Equilibria between these two extremes exhibit bo th a small net positive charge within the beam channel and partial current neutralization. (C) 1999 American Institute of Physics. [S1070-664X(99)0400 9-4].