Moving Striations in the Argon Positive Column. I. Theory

The equations governing the plasma in the positive column of a dc discharge are analyzed for wavelike perturbations about equilibrium. Conservation-of-number equations are used for ions and metastables; the Boltzmann equation is used for electrons. The tail of the distribution determines the important source terms in the number equations. The equations are solved numerically for several cases in argon to determine the properties of the waves. Growing waves that propagate from anode to cathode are found for densities below a critical value, corresponding to the Pupp limit. The group velocity is in the opposite direction.