Royal Society Publishing

A comprehensive treatment of the positive column of discharges in electronegative gases

R.N Franklin


Fluid equations are used to describe the plasma which is the positive column of a gas discharge in electronegative gases. These equations are solved computationally over a wide range of the parameters needed to characterize the plasma when attachment, detachment, recombination, ionization and particle collisions are significant processes. Where possible, comparison is made with results obtained by the method of matched asymptotic approximations. The conditions under which discharges may exist are elucidated and it is shown that it is necessary to include ion diffusion, through the ion temperature, to get realistic distributions of the ions at higher pressures. The conditions under which such discharges are structured are obtained with the general requirement that the attachment rate must be less than the ionization rate for there to be a central ionā€ion plasma core. Equally, the nearly collisionless situation is described in detail in the fluid approximation.