A bi-temperature plasma under a strong Hall effect (over the critical value) is subjected to the Velikhov instability occurrence. In a paper published and submitted in 2008, we were reporting on this instability growth rate.
The Velikhov instability is a plasma turbulence, which growth rate is similar to ionization time and strongly spoiled by a non-linear behavior. It completely destroys the desired expected spiral pattern. Cancelling this instability is therefore the sine qua non condition to the development of MHD devices cruising at hypersonic speed and high altitude.
|The Velikhov instability development||Canceling the instability andshaping the streamer|
When cold plasma, bi-temperature is subject to a transversal magnetic field, the electro thermal instability quickly arises as the Hall parameter exceeds a critical value depending on the plasma characteristics. The typical growth rate of this instability is nearly similar to the ionization rise time. The plasma then becomes highly non-homogeneous, increasing the global electrical resistance of the streamer.
The magnetic field spatial distribution, in steady state mode, is modulated in such ways that it should be weaken where the streamer is supposed to appear, i.e. between anode and cathode. Hence, the associated Hall parameter local value is lowered, thus increasing the electric conductivity local value.