A theory of ion-guided and metastable-guided varieties of ionization waves (striations)

The well-known two varieties p and r of ionization waves (striations) in neon are explained as ion-guided and metastable-guided ionization waves with essentially identical propagation mechanism. To obtain both waves as a solution, in the basic system of equations the time-derivatives in the continuity equations for both the ions as well as the metastables are taken into account. At low discharge currents, the rate of change of the metastables is slower than the rate of change of ion density, and both wave varieties develop separately and can exist simultaneously.The hydrodynamic equations are used for the formulation of the theory and the electron energy distribution is characterised by the mean energy. The Druyvesteyn distribution for electrons (instead of the usually used Maxwellian distribution) is used for calculation of the transport coefficients of the electron gas at the low currents, while the dependence of ionization and excitation rates on the mean electron energy is chosen by trial only and fitted to experimental characteristics of the waves. With non-maxwellian transport coefficients, an instability of the ion-guided wave occurs without any influence of stepwise ionization.The authors are deeply indebted to V. Krejí and O. tirand for their valuable remarks, and also T. Rika for providing his recent results and for enlightening discussion.