Instabilities by hall currents in a weakly ionized plasma

In a hot cathode discharge tube with a coaxial electrode configuration, low frequency oscillations (300 c/s - 30 kc/s) propagating in the direction of E x B (where E is a radial electric field and B_o is an external magnetic field) are observed when B_o exceeds a low critical value. The used gas is Ar and Hg. The results of the experiments are in agreement with a theoretical analysis based on the fluid equations taking into account the collisions between charged and neutral particles. Oscillations are caused by a azimuthal macroscopic relative velocity between electrons and ions. For the case of low pressure, the oscillations seems to be ion acoustic waves. But these seem to be drift waves if the pressure is so high that the collision frequency is larger than the frequency of oscillations. (author)