Cold plasma stabilization of a mirror-confined, hot-electron plasma

The stabilization of a hot-electron plasma in a simple mirror geometry is investigated. Controlled quantities of neutral gas generate a cold plasma through hot-electron ionization. Increasing stability is found with increasing gas pressure. The pressure required for stabilization is found to be inversely proportional to the ionization cross section of the type of neutral gas, indicating that the number of cold electrons is the key stabilizing quantity. The stabilization requires the cold electron density to be at least the same order of magnitude as the hot electron density. Line tying to external surfaces does not play a role in the stabilization. A theory in which the electrons, but not the ions, can be treated in the drift approximation is most closely applicable to the experiment. Reasonable agreement between theory and experiment has been obtained.