Long-term stability of a one-dimensional current-driven double layer

Long-term (>an electron transit time over the system) stability of a one-dimensional current-driven double layer is studied by numerical experiments using particles. In these experiments, the potential difference across the system is self-consistently determined by the space charge distributions inside the system. Each boundary of the system supplies a nondrifting half-Maxwellian plasma. The current density is increased by increasing the number density of the source plasma at the injection (right) boundary. A double layer can be developed by injection of a sufficiently high current density. For a fixed level of current injection, plasmas carrying no current with various densities (n/sup ts/0) are loaded on the left side of the system. Whether or not the generated double layer can maintain its potential drop for a long period depends on the density (n/sup ts/0) relative to the initial density (n/sup */0) near the injection boundary: (1) the double layer is found to grow when n/sup ts/0 = n/sup */0; (2) the steady double layer is seen for a long period when n/sup ts/0approx. >n/sup */0; (3) the double layer is found to decay when n/sup ts/0 is even higher than n/sup */0. A new concept of the current polarizability P/sub c/ = J/n/sup number/ is introduced for understanding these results, where J is the current density flowing through the double layer and n/sup number/ is the plasma density at the injection front, i.e., the low-potential edge of the double layer