Density Limit for Electrostatic Ion Confinement Using the Space-Charge of an Electron Plasma*

The density limit for ions electrically trapped by the space charge of an electron plasma is studied numerically and reported. A non-neutral plasma with a Boltzmann distribution is considered via a self-consistent finite-difference evaluation. A constraint on the maximum electric field at the plasma’s edge is expected to limit the ion density. The functional dependence of the normalized electric field on the following parameters is evaluated using a parameter study by varying: the charge density of the positive plasma species at the system’s center normalized by the electron charge density at the system’s edge, the average of the positive plasma species’ charge state multiplied by the ratio of the electron temperature to the temperature of the positive plasma, and the normalized distance from the center of the system to the system’s edge. This dependence is fit with a function that is used to determine the ideal parameters for ion density maximization.