Acta Polytechnica April 2013 Volume 53 num 2 page 219-222

J.P. Petit and J.C. Dore

When a two-temperature, cold plasma, is submitted to a transverse magnetic field, the electrothermal instability takes place very rapidly, if the local value of the Hall parameter is greater than a critical value, which depends on the local plasma parameter’s values. The characteristic growth time of this instability is close to the ionization time. The plasma becomes very inhomogeneous, which increases the global electric resistance of the streamer. Pictures show the characteristic light streaks. The cancellation method is inspired by the one presented by the author in 1983 at the international MHD meeting of Moscow. The spatial distribution of the steady state magnetic field is designed in order to reduce its value where a streamer, linking electrode and cathode, is supposed to take place. Thus, the corresponding local value of the Hall parameter is weakened, which rises the local value of the electrical conductivity. We get a favourable non-linear positive feedback. To a strongly non-linear well-known phenomenon we give a strong non-linear remedy. The subsequent rise of the electrical conductivity enhances the electrical current density and, subsequently, the electron temperature. The local rise of the degree of ionization and the ion density makes the plasma to shift it into locally local coulomb dominated regime. This produces a collapse of the Hall parameter, under the critical value, corresponding to a fully ionized plasma regime, which is close to 2.

As a result the Velikhov instability cannot take place, which is successfully confirmed by the perfect homogeneity of the plasma in the streamer, as shown in the pictures. By the way, the weakened B-field lane behaves somewhat like a rail, giving a possibility of electric current guidance.

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