Ionization wave as an Instability — Evolution and Nonlinear Effect

Abstract

Evolution from the linear growth to the nonlinearly saturated state of ionization waves (moving striations) is investigated from a viewpoint of an instability which appears in a plasma. The experiments were performed observing backward waves excited below the upper critical current I, in xenon, argon, and argon-mercury gases at pressures of the order of Tom. It is found that (1) the behavior of the evolution obeys the Landau amplitude equation; (2) the saturated amplitude does not depend on an initial value, but only on plasma parameters; (3) the linear growth and squared saturation level are proportional to the excess over I,, and when frequency-controlled, they have a parabolic dependence on the frequency; and (4) nonuniform axial changes in the dc state due to the nonlinear effects appear in a form of enhanced ionization in the plasma where the electron temperature and density are increased. The way of these behavior can be applied to a large number of spatially or temporally unstable modes.

Microinstabilities in plasmas-non-linear effects

“…Equations of this form have been verified as applying to drift waves (Wong and Hai 1969) and to ionization waves (Sato 1973) and also to the decay instability l + l + s (Franklin et a1 1975b) under some conditions.…”

The anomalous behaviour of the positive column in an axial magnetic field

“…It was found in a previous paper (Sato 1973) that the positive column with ionisation waves has, due to some nonlinear effects, slightly higher values of the DC component of the axial electric field and electron temperature than the homogeneous column. The anomalies reported here are probably related to nonlinear phenomena of the waves.…”

Critical Current of the Ionization Waves and Anomaly of the Positive Column in an Axial Magnetic Field

“…The waves exponentially grow from an initial sinall signal with the linear growth rate ki,A a exp ( k i z ) , and finally saturate with a level A , of the amplitude. In this case the values of X-i and A , depend on the plasma (discharge) parameters only, independent of the initial amplitude and the external circuit condition[8,9]. Near the critical boundary for wave appearance,quantities k, and A,a are related to a discharge parameter p as k,, Aa2 0: pcp , where p, is the value at the critical houndary for which ki = A , = 0, and other paraiiieters are remained constant,.…”