Low-Frequency Waves and Instabilities on the Positive Column in a Magnetic Field. V. Axisymmetric Ionization Waves

The perturbation theory of the positive column in a magnetic field is extended to the nonisothermal case by allowing for fluctuations in Te and ionization rate, using the electron energy equation. The model assumes a homogeneous plasma, which is a satisfactory approximation for m = 0 modes. The ion-acoustic and electron waves of isothermal theory are modified and, more importantly, a new temperature or ionization wave arises. The latter can be unstable and is the linear form of striations. Measurements are presented of the dispersion characteristics of externally excited m = 0 ionization waves on a He column in the pressure range 38-600 mTorr and field range 0-400 G, which covers the transition from spatially damped to growing waves. Good agreement is obtained between the calculated and measured dispersions.