In the work reported, the possibility of using a nested Penning trap as a high purity source of low‐charge‐state ions is studied. For the configuration considered, a relatively dense ion plasma is confined by a three‐dimensional electric potential well. The three‐dimensional well is produced by the electric field generated by both the trap electrodes and a trapped electron plasma. The ion and electron plasmas are each considered to have Maxwellian velocity distributions. However, it is shown that the electron plasma must have a temperature that is higher than that of the ion plasma when the ions have low charge states. The work reported includes a self‐consistent prediction of a possible plasma equilibrium. © 2003 American Institute of Physics